Table of contents Pdf

Home

1. lo A Cancel Chapter 4 Analysis of measured data 67 Fig 45 Peak search results window Peak search results Results No Position Height Area Width 1 2 Derivative Me 1 72e 8 i 5 40e 7 Peaks are normally searched in the scan direction If this is not required the Reverse option in the upper right corner of the window should be checked In the Baseline panel it can be checked whether or not the peaks found will be corrected for the baseline This baseline is determined by means of the tangent fit method The tangent is drawn from the left side to the right side of a peak if linear baseline is checked In cyclic and linear sweeps it may be better to use only the front of the peak to construct the tangent This is done when Lin front baseline is checked If the automatic peak search method fails the Automatic search should be switched off Two alternatives are present curve cursor and free cursor In both modes two points need to be marked the beginning and the end point of the peak In curve cursor mode the markers are automatically put on the voltammogram In free cursor mode the marks can be put everywhere on the graph In curve cursor mode the two markers several types of basecurves can be drawn linear 3rd order polynomial or exponential Moreover in case of double peaks only peakheight of the front peak the rear peak or highest in the whole selected
2. Files of type Cv iow y Cancel 4 Chapter 2 Getting started with GPES 11 4 In the Edit procedure window you will now find all the measurement parameters By clicking Start the program will start the dummy cell measurement During the measurement you can automatically rescale the curve in the Data presentation window by typing F4 on your keyboard Fig 3 Results of procedure TESTCV Data presentation ex File Copy Plot Analysis Editdata Work scan Test of cyclic voltammetry on dummy cell WE a Compare with standard plot 0 125x10 0 100x10 4 JA 0 075x10 4 0 050x10 0 025x10 04 0 025x10 4 0 050x10 4 0 075x105 4 0 100x10 4 0 125x10 1250 1 000 0750 0500 0 250 0 0 250 0 500 0 750 1 000 1 250 E V 5 After the measurement is done the curve should look like the curve in figure Results of procedure TESTCV i e a straight line if not please consult the Installation and Diagnostics guide in this manual 6 In the Edit procedure window please select Number of scans and change the value from 1 to 100 If you now press start again the program will start to do 100 scans You can always stop the measurement by using Esc on your keyboard or by clicking the Abort button Please do so after a few scans After stopping the Data presentation window will show you the last scan You can also select one of the previous scans by
3. Chapter 3 The GPES windows 51 Options The Options menu encompasses the following items Trigger Under this item the option Trigger is present After selecting this option the following window appears In this window the trigger pulse can be configured Fig 27 The Trigger option window Trigger option Trigger option I Enable trigger pulse option Start measurement on input trigger TTL The trigger pulse can be a change from low to high or from high to low It should last at least 1 ms React on Abort Advance button during wait for trigger The trigger pulse should last at least 10 ms O Give output trigger TTL The trigger is given after pretreatment and equilibration at the start of the measurement Immediately after the measurement the output is set as before the measurement Output from low to high Output from high to low rs ae DIO connections Use pin number 1 8 1 Pin 25 is the digital return lead of the Autolab Use port P1 of P20 Please note that there is a risk of introducing a ground loop when connecting an external instrument to Autolab This results in a higher noise level on the potentiostat OK After enabling the trigger pulse option the Start button has to be clicked The program will go through pretreatment and equilibration and will then wait for the trigger signal 52 User Manual GPES for Windows Version 4 9 end of measurement
4. staircase cyclic differential pulse normal pulse square wave voltammetry voltammetry voltammetry voltammetry reversible reversible reversible reversible quasi reversible quasi reversible quasi reversible quasi reversible irreversible irreversible irreversible irreversible ErCi irreversible ErCi irreversible ErCi irreversible ErCi chemical reaction chemical reaction chemical reaction irreversible chemical reaction two component In all the above models it has been assumed that the experiment is carried out on a stationary electrode in an unstirred solution The fit and simulation works only with staircase voltammograms but not with linear scans Moreover in cyclic voltammetry the current measured during a potential step depends on the history of the scan i e on the number height and duration of all preceding steps This means that for the sake of speed the number of potential steps should in the scan should be kept small The simulation method Digital simulation of current potential curves is based on finite difference method Equations of the transport of electroactive substances to the electrode surface are solved by Crank Nicolson technique a method widely used by electrochemists and renowned for its accuracy and stability The time dependent concentration profiles obtained from these equations are used for the calculation of the current The advantage of digital simulation is its versatility This feature i
5. a Manual control x Current range Settings Potential iR compensation o CHA a Alle F 100 mA J a L Le O B10mA 000 y 0 Ohm i 1mA Pe 100uA Integrator Pe 10uA Current O0 01s O h1uA 00 A Potential Cols 7 100nA Co noise Oils T10nA 10s Filter 005 Y O Potential ee Em yy tai The Manual control window allows you to control the potentiostat manually instead of via a measurement procedure With the dummy cell still connected to the cell cable and the procedure testcv loaded you can try the following 1 Clicking the highest current range 10 mA for a PGSTAT10 uAutolab 100 mA for a PGSTAT12 100 and 1 A for a PGSTAT20 30 results in the selection of all current ranges except the 100nA range This allows automatic current ranging using all the checked ranges during the execution of a measurement procedure The green circle indicates which current range is active Check this by clicking on one of the circles and see what happens on the front panel of the potentiostat 2 The cell can be switched on and off manually please click the cell on off button and check the result on the potentiostat 3 By using the slider below Potential it is possible to set a potential value Make sure that the cell is on and use the slider to set a potential of 1 V In the Manual control window the current and the potential are given By clicking the Clock on off button the program wil
6. 78 User Manual GPES for Windows Version 4 9 Simulation 1 Load the differential pulse voltammogram C autolab testdata demoea01 2 Set a window see Plot menu on Data presentation window between 1 150 and 0 850 3 From Analysis menu Data presentation window select Fit and Simulation 4 Select the model reversible from the drop down menu in the top part of the appearing window and set the simulation mode by activating radio button Simulation s Switch on extended setup option Extended setup in the Option menu or Ctrl E 6 Set values of parameters 7 Check whether the type of the process oxidation reduction is set correctly s Each parameter has its allowed range If a value is entered that exceeds this range it is automatically adjusted to fit within it 9 If necessary adjust simulation options Fit control parameters in the Options menu For details on these options see Simulation advanced options 10 The Init guess button can be used all the time to obtain estimates of parameters for the work data u Press Simulation button or Alt S to start calculations 2 When simulation is completed the status field shows message simulation ready The x field displays the sum of squares of datapoints values y 3 The comparison can be improved by switching to Fit and selecting Full Fit To make simulation results permanent select the Make work data option from the File menu Close the fit and simulation win
7. i 1mA Seva deta As p 0 O Pe 100uA High Stability Integrator e 0 O Re 10uA Current 00 01 s Delete files 10 ORIA Potentiostat 00 l A O Potential O01ls Exit F 100nA a Ois easuremen Filna iB comp off i0s Number of scans 5 O Time pra a ECD off 005 Y Potential C Remote Of Ols u Remote Cell off after measurement m Ols O5s E E noise oa Standby potential V 1 E Data presentation fol x Potentials File Copy Plot Analysis Editdata Work scan Define start potential w r t OCP M 0 400x10 Ferri Ferro O Start potential V 398 A Cyclic voltammetry a 0 300x10 First vertex potential V 6 domiti Second vertex potential V 4 dy 3 Step potential V 00244 lt q 0 100x10 Scan rate V s 099992 0 0 100x10 0 200x10 0 300x103 T T T T Title and subtitle 0 500 0 250 o E V 0250 0 500 0 750 Feri Ferro Ej E 005V 1 00A Status Messages Disk file Q 1 543E 03 C Q 9 369E 04 C Manual control A Start QJ Exploring Paint Sho B GPES lEditproc Dj Manual c A4 Data pres BR Screen C QJ Exploring 400PM Open procedure A procedure is a file containing all the experimental parameters It contains measurement parameters potentiostat galvanostat settings and graphics display values The extension of the file which is mentioned in the File name field should not be changed The directory in which the procedure fi
8. of x File Method Utilities Options Project Window Help cala 418 18 Cyclic voltammetry staircase Normal Procedure DEMOCV01 lu Wave log analysis Data presentation File Copy Plot Analysis Editdata Work scan Results Commands Ferri Ferro E1 2 0 157 Continue Cyclic voltammetry Height 51 474E 5 So Alpha n 25 C 557 A Intercept 3 375 E 2 504 la Corr coef 999 5 She No points 62 Close E R Messages Status Disk file Q 1 543E 03 C Q 9 369E 04 C Analysis Wave Log HA Start E aPES Mana A Exploring P El Edit procedure El Manual control Uy Data pres ES Paint Shop Prol E Wave log an 10 29 AM 9 From the GPES manager bar choose File and Print the Print menu allows you to print the measured data one or more of the windows and a Template Select Template and Set up template With this option you can print a measured curve together with the most important measurement parameters on one sheet With Insert and Field you can add or remove fields with parameters from the template You can also drag fields around to put them on another place on the sheet By clicking File and Print preview the values for the parameters and the curve are shown The size of the curve may be changed by clicking it with the right mouse button and then moving your mou
9. some important procedure parameters Date 26 May 97 Time 14 12 17 Exp Conditions Linear sweep voltammetry Begin potential V 0000 End potential V 1 0000 Step potential V 02441 Scan rate V s 99992 Equilibration time s 10 Number of Data Points 42 Potential Scan 1 Scan 2 0 024414 1 191406E 07 1 232910E 07 Load data buffer This option can only be selected for data from cyclic and linear sweep voltammetry Allows to load the complete set of scans see Save data buffer This is only possible if in the start up menu Autolab applications has been chosen Delete files This option allows to delete procedures and measured data files The File window shows only the procedure files A selected procedure will be deleted from disk together with corresponding data files A delete action can not be undone Exit The GPES window will be closed and the program is exited The program settings are stored on disk 32 User Manual GPES for Windows Version 4 9 Method The required electrochemical technique can be selected with the Method menu The type of experiment parameters in the Edit procedure window will change depending on the selected technique For more information see the manual section on Electrochemical methods Fig 16 The Method menu 1 GPES Manager Manual control of x Eile Utilities Options Project Window Help Voltammetric analysis Cyclic voltammetry staircase Normal Pr
10. NFACpux D Ttm tanh nF AE 4RT where tm is the modulation time and AE is the modulation amplitude Differential pulse voltammetry quasi reversible electrode process ne ks Reaction equation R P Fitable parameters peak potential Ep V Log normalised electron transfer rate log k transfer coefficient a peak current J A constant background current A 92 User Manual GPES for Windows Version 4 9 Initial guesses available for number of exchanged electrons Ep log k Ne a Ip background current Comments The parameter log k is a 10 base logarithm of the electron transfer rate Ss normalised with respect to the time scale of the experiment k k t D where V is the scan rate and k is the electron transfer rate used in Butler Volmer equation I k e exp anF RT E E c exp l a nF RT E E The general expression for the peak height does not exist expressions for particular situations are complicated Differential pulse voltammetry irreversible electrode process ne ks Reaction equation R gt P Fitable parameters Characteristic potential E V Log Normalised electron transfer rate at E 0 log k 2 exchanged electrons transfer coefficient an peak current Jp A constant background current A Initial guesses available for number of exchanged electrons Ep log k an Ip background current Comments There is no need to set the number of exchanged electro
11. The potential goes from the start potential to the first vertex potential where it turns around to go to the second vertex potential Show noise around zero Volt ECN with ECN module selected If checked the potential noise will be plotted around zero volt in stead of around the DC potential Signal multiplier Second signal CV CM The recorded second signal is measured in Volts It can be multiplied by a factor to convert it into another unit Signal offset Second signal CV CM The recorded second signal is measured in Volts An offset can be supplied to convert it into another unit Smooth level PSA The potential time data are recorded Subsequently the data are smoothed using the Savitsky Golay algorithm and the derivative dt dE is calculated See for further details the section on smoothing Specify cutoff value for ys signal CV CM interval times gt 1s If checked the 2 signal will be checked on the Cutoff value for one signal gt V and Cutoff value for 2 signal lt V The measurement will stop CV or proceed with the next potential level or stop if it is the last potential level in the sequence CM Specify current boundaries CV normal or stationary current mode If checked the scan direction will be reversed if the current exceeds one of the values specified below In case of linear sweep voltammetry the recording of the scan will be terminated Specify
12. This option is present in the File menu of the Data presentation window The file with the extension IMP has the following layout Date 02 May 97 Time 13 24 39 Frequency Hz 252 020 Amplitude Vrms 001 Phase sensitive Yes Phase degree 20 000 E V i ac A Z ohm phi deg Rs ohm Cs F NOTE These data are additional data and can only be obtained after the measurement NOT after loading a data file Quick save of previous scan When a Cyclic or Linear sweep voltammetry measurement with more than one scan is going on it is possible to save the previous measured scan This option can also be activated by typing SAVE on the keyboard This option work similar to the procedure parameter Save every nth cycle Save as Chrono data Save a Step segment of Steps and Sweeps as Chrono methods data This data file can be read in Chrono methods in order to perform data analysis Save as Linear sweep data Save a Sweep segment of Steps and Sweeps as Linear sweep data This data file can be read in the Linear sweep method in order to perform data analysis 58 User Manual GPES for Windows Version 4 9 Copy The Copy option allows to copy the graph to clipboard or to dump the graph in a bitmap file BMP These files can be read by programs like Paintbrush Excel or MS Word These programs allow editing of the graphs The best result is obtained by doing this from a maximised Data presentation window By default GPES only dra
13. and can be saved on disk using the File option on the Data presentation window Appendix II Combination of GPES and FRA 127 Appendix Ill Combination of GPES and FRA The FRA and GPES programs can be used at the same time Moreover a FRA project file can be executed from GPES The command FRA Start lt filename gt is available for this purpose However in general it is important to note that both programs share the Autolab instrument and the graphics part of the software Moreover both programs require a considerable amount of the system resources This means that when both programs are active hardly any system resources are left The amount of free system resources can be seen in option About program manager in the Help menu of the Program manager window Practical rules are The computer should be equipped with at least 32 MB RAM It is not possible that both programs are measuring and controlling the Autolab instrument Before the FRA program starts measuring the sleep mode in GPES is automatically switched on This means that the GPES screen is no longer updated Do not use function keys when both programs are active because they will cause actions in both programs When a measurement procedure is being executed user interaction with the programs should be avoided Apart from GPES and FRA no other program window should be active Appendix IV Multichannel control 129 Appendix IV Multichannel control It is possible
14. lt filename gt Dataset Subtract lt filenamel gt no lt filename2 gt lt filename3 gt Utility SetRDERPM lt rpm gt Results Clear Results SaveAs System Run lt filename gt System Beep Print Template Print Plot Print Procedure Print Results FRA Start lt filename gt Utility Channel lt n gt Utility NextChannel Chapter 3 The GPES windows 45 project command to store impedance data measured for AC voltammetry The extension is IMP The filename must be specified without an extension subtract files and save the result in another file lt filename3 gt lt filenamel gt lt filename2 gt set the Rotating Disk Electrode to a specific rotation speed The set up of the RDE is made in the RDE control option under Utilities clear the Results window save the Results window execute another program and wait until it terminates The System Run command search for the program file with the next sequence PIF EXE COM BAT give a beep print a hardcopy according to the template print a hardcopy of the Plot window print a hardcopy of the measurement procedure print a hardcopy of the Results window start a FRA project file from GPES lt filename gt should be a FRA project file sets the active channel to lt n gt The MUX will be automatically enabled when necessary increase the active channel number with one If the channel is not available the act
15. 1 000x10 4 Corrosion rate Fit Tafel Slope Commands 1 000x10 4 i corosion 1 129E 5 A corrosion 2 258E 6 A cm2 1 000x10 Pp 9 568E 3 Ohm 0 600 0 550 0 500 0 450 0400 0 350 0 300 0 250 Iteration 32 Chi square 3 077E 12 Ecorr obs 319 Y Ed 509V 202V Corrosion rate 2 622E 2 mm year Status Messages Disk file Q 1 653E 04C Q 1 947E 04 C MStar 804wa Ey Inbox Outlook Ex GY Exploring R FIG EE GPES Manager M dp Microsoft Photo E PY Microsoft Word G Bo 4 G2p 16 38 nalysis Corrosion rate Chapter 4 Analysis of measured data 73 The corrosion rate is determined on the basis of the equation 1 i Icorrosion 4 exp sl E Ecorr Xp s2 E Ecorr J where sl slope of the anodic branch 2 303 b s2 slope of the cathodic branch 2 303 b Eeq the equivalence or corrosion potential icorrosion the corrosion rate or exchange current in Ampere When the Start fit button is clicked a fit is performed on the slopes and the corrosion current The observed corrosion potential i e the potential where i 0 is taken as the corrosion potential Esorr The fitting is performed according to the non linear least square fit method of Levenberg Marquardt The values obtained from the Tafel lines are used as start parameters After some iterations the fit results are presented on the screen Also t
16. 1295 A corrosion 2 258E 6 Avom2 1 000x10 4 Rp 9 568E 3 Ohm 0 600 0 550 0 500 0 450 0400 0 350 0 300 0 250 Iteration 32 Chi square 3 077E 12 Ecorr obs 319 V E V E begin 509V E end 202 4 Corrosion rate 2 622E 2 mm year 1 Status Messages Disk file Q 1 653E 04C Q 1 947E 04 C nalysis Corrosion rate Aston E El del BY G Bindox Outlook Ex GY Exploring R FIG E GPES Manager M ip Microsoft Photo E WY Microsoft Word 6 BOA GBD 16 38 In this window the program shows a first value for the corrosion potential as well as for the polarisation resistance Furthermore you can specify values for the surface area the equivalent weight and the density of the material you are using For this example you can set these values to 1 Click the Tafel slopes button You are asked to set markers on the anodic branch and on the cathodic branch After you have done so the Corrosion rate window appears with a list of parameters among which the corrosion rate in mm year By clicking the Start fit button the software will adjust the parameters until a best fit of the original curve is found This fitted curve is shown in black and the final values for the parameters are given Click close and transform the vertical axis of the curve back to linear 2 5 Noise reduction Make sure that the method is Cyclic voltammetry staircase normal 1 Load the datafile democv04 from the autolab
17. 500 15 000 GJE Status Disk file Messages nalysis Endpoint Coulometric titration GN Start EHP Status Window E GPES Manager Man BF Microsoft Word Coulomet Parameters Filter for derivative Window for zero crossings Comba AR 14 48 Filter factor to reduce noise on the 2 derivative 1 no filtering 25 heavy filtering Defines when a zero crossing should be noticed as a real zero crossing This window defines the amount of points with different sign before and after the zero crossing Due to Faraday s law the equivalent of generated titrant is proportional to the charge and the equivalent of the analyte can be calculated see also Application note Coulometric titration and Installation and Diagnostics Guide pX module Chapter 5 Editing of measured data 97 5 Editing of measured data 5 1 Smooth Every measurement is disturbed by noise In many cases the noise level will be low but especially at low current levels the amount of noise can be severe In order to enhance the signal to noise ratio of experimental data sets a Smooth option is supplied The data files can be smoothed using either the Savitsky Golay algorithm or a FFT algorithm Smoothing can be performed on the whole curve or a part of it When only a part of the curve should be smoothed click the Smooth window button and select a part of the curve The remainder will not be smoothe
18. L i high e E pretreatment equilibration measurement Rescale after measurement Enable or disable automatic rescaling directly after the measurement of a voltammogram Rescale during measurement When this option is activated the graph in the Data presentation window is rescaled when a measured data point is outside the boundaries of the plot Procedure name in Data presentation Window With this option it is possible to print the procedure file name on the Data presentation window This is useful to identify the graph when it is dumped on a printer Show all GPES files in File dialog box If this option is activated all files of all techniques are shown in the File dialog boxes of the File menu The program will switch automatically to the appropriate method Window The Window option allows the selection of windows which should be shown on the screen The Tile option gives the default partitioning of the screen The Close all option will delete all the GPES windows except for the status bar and the GPES Manager window Help The Help option is the top entry point in the help structure For most topics on the screen Help is available By pressing F1 the specific information about the part of the screen on which has been focused is given Tool bar The tool bar contains a list of buttons the current electrochemical method and the name of the current measurement procedure The buttons give short cuts to vario
19. RbD Xbt where the first term is equal to the fitable parameter norm and the function x bt b QnFV RT represents the shape of the voltammetric peak The peak value of this function depends on the electron transfer rate ks the transfer coefficient o the step height step time and the current sampling parameter 0 Cyclic voltammetry irreversible electrode process ne k Reaction equation R gt P Fitable parameters Log Normalised electron transfer rate at E 0 log k a exchanged electrons transfer coefficient on normalised current Jnom I fnorm X LD A constant background current A Initial guesses available for E AN Inorm background current Comments The parameter log k o is a 10 base logarithm of the electron transfer rate normalised with respect to the time scale of the experiment k i e RT nFVD where V is the scan rate and Pa is the electron transfer rate at E 0 used in reduced Butler Volmer equation I k cp exp cmF RT E k c exp onF RT E E According to the theory the peak current is equal to nFAcpux M bD x bt where the first term is equal to the fitable parameter norm and the function x bt b QnFV RT represents the shape of the voltammetric peak The peak value of this function is equal to 0 4958 for linear sweep voltammetry and for staircase voltammetry it depends on the electron transfer rate ks the transfer coefficient a the step height step tim
20. User Manual GPES for Windows Version 4 9 Characteristic potential E V Log normalised electron transfer rate at EO 0 log k gt exchanged electrons transfer coefficient an peak current Jp A constant background current A Initial guesses available for E lp background current Comments There is no need to set the number of exchanged electrons because the term Qn is fitted as a whole The characteristic potential E is defined as E RT onF ink E RT anF Ink where kp k gt fDp and k k D k e W RT nFV D_ where fis the frequency and k and Xp are the electron transfer rates used in simplified Butler Volmer equation I k cp exp onF RT E k c exp onF RT E E There is no simple expression for the net peak current The interpretation of the value of Jp depends whether fitting takes place on the net current or on forward backward currents in the first case Ip corresponds to the height of the net current in the second to the height of the forward peak Switching between net current and forward backward current will therefore result in the difference in peak heights Square wave voltammetry reversible electrode process followed by irreversible chemical reaction ECi Reaction equation R gt P o B Fitable parameters redox potential E V normalised forward chemical reaction rate kc foll gt norm k of peak current J A constant background current A Initial guesses
21. Using a convolution method the effect of the decrease of the concentration gradient can be eliminated from the total response of the electrode The surface concentration of the product of an electrode reaction during the experiment can be obtained using equation c t i t 9 t nFAD eq 1 where i f g f is a convolution operation defined as f x f2 x f u f2 x u du f x u f2 u du eq 2 O gt J 0 The function g t depends on the transport conditions and the electrode geometry being in the simplest case 111 The convolution of a voltammogram results in an S shaped curve where voltammetric peaks are replaced by waves very similar to polarographic ones In the case of a fast and uncomplicated electron transfer the wave can be described using the equation E Ey RTINF In mm m eq 3 where m denotes current convolution for approximate description of kinetic controlled processes the RT nF value should be replaced by RT anF The height of the plateau is given by the formula ma nFAD C eq 4 It can be shown that such a result is independent of the scan rate used and that the height of the wave is insensitive to R drop Convolution of voltammetric data with a f function results in a curve equivalent to the derivative of the previous one up to a normalisation factor Valuable features of this new curve can be noted symmetric narrow peaks which are much better resolved compare
22. a user defined set of measurement parameters and a copy that can be scaled of the current graph The Setup template option allows to edit the template The parameters on the template can be selected using the Insert menu option The parameter position can be dragged over the screen with the mouse The comment text as well as the attribute of the item with focus can be edited by double clicking on 1t If you have changed the template according to your requirements please do not forget to save it see corresponding File option The rectangle in the template is the Graph frame The focus is on the frame after a click in the frame If the left hand mouse button is pressed down within this frame it can be dragged If the right hand button is clicked the lower right corner of the frame jumps to the mouse cursor and is subsequently attached to the mouse cursor This allows you to adjust the frame size After a click with the left hand mouse button the attachment is broken The appearance of the graph in the print out of the template depends on the actual size and shape of the Data presentation window The print of the template will cover half a page if printed in portrait and a full page if printed in landscape See print setup On the print out the parameter values also appear The print out can also be previewed see corresponding File option Load data sometimes called Load scan Allows to load previously measured data from disk I
23. allows to fit a straight line through a part of the measured curve When the option has been selected two windows appear One is the Linear regression window and the other is the Markers window When the user has marked the begin and end point of the line on the measured curve and has clicked the OK button a line is drawn so that the sum of squares of the differences between measured and calculated value is minimum 70 User Manual GPES for Windows Version 4 9 Fig 48 Linear regression window Linear regression T Results l Commands Slope 2 024E 3 Xbegin 0 061 1 Slope 4 940E 2 Y begin 7 507e 5 Intercept 5 070E 5 end 0 117 Corr coeff 0 999 Y end 1 87 7e 4 The slope of the line dY dX its inverse the intercept the value at X 0 the number of points between begin and end point the standard deviations and the correlation coefficient are displayed in the Linear regression window More lines can be fitted when the Set line button is clicked 4 5 Integrate between markers This operation will determine the area under the curve between two selected points With cyclic voltammetry the area is expressed as charge C Thus the calculated area is divided by scanrate 4 6 Wave log analysis The Wave log analysis option is active for voltammetric analysis and cyclic and linear sweep voltammetry The half wave potential Ey can be determined and Tafel slope analysis can be done for a S shaped cyclic
24. and the base line respectively the limiting line is defined as the quantity tau The crosspoint of the transition line with the baseline is called t base of tau Finally also the quantity E3 4 El 4 is given This is the difference in potential at three quarters of tau and at one quarter of tau Subsequently the plot can be transformed dependent on whether the measured system is thought to be reversible or irreversible Finally a linear regression can be done to extract the kinetic parameters from fitting a straight line An example of transition time analysis is given in the chapter Getting started with GPES 4 13 Fit and simulation The Fit and simulation option is located in the Analysis menu of the Data Presentation window It provides the method to determine parameters of electrochemical processes like formal redox potential heterogeneous rate constant transfer coefficient amp etc as well as to simulate theoretical current potential curves The table Chapter 4 Analysis of measured data 75 below summarises the models i e combinations of experimental techniques and reaction mechanisms for which fitting and simulation are currently available The models available for fitting and simulation are extended with the mechanisms in which two parallel reactions are involved The models are called two component models and are available for the cyclic voltammetry technique Table 2 Models available for fitting and simulation
25. available for Ep Ip background current Comments The forward chemical reaction rate is normalised with respect to the time scale of the experiment ky k f where fis the frequency There is no simple expression for the net peak current The interpretation of the value of Jp depends whether fitting takes place on the net current or on forward backward currents in the first case Ip corresponds to the height of the net current in the second to the height of the forward peak Switching between net current and forward backward current will therefore result in the difference in peak heights Chapter 4 Analysis of measured data 95 4 14 Current density The current density is calculated with the surface area using the surface area on page 2 of the procedure window 4 15 WE2 versus WE plot When a BIPOT is present Iring versus Idisk plots can be constructed with this option 4 16 Endpoint Coulometric titration After performing a coulometric titration experiment Chrono method gt 0 1s potentiometry galvanostatic with pX pH signal this option can be chosen The experiment time is converted into charge the current applied is given from the procedure and only the pX pH signal is shown on the y axes Furthermore the Endpoint Coulometric titration window is opened to find the endpoint If you follow the instructions the turning point will be shown as endpoint The endpoint is obtained from the zero crossing s in the 2 d
26. but the number of operations is linearly related to the number of Chapter 5 Editing of measured data 109 data points For details refer to Pajkossy T Nyikos L J Electroanal Chem 179 1984 65 Spherical convolution The algorithm is used to carry out convolution of the data measured using a spherical electrode and staircase potential waveform Values of the diffusion coefficient the electrode radius as well as the delay between begin of the potential step and the current sampling moment are necessary The number of operations is proportional to the square of data points Details of the algorithm can be found in S O Engblom K B Oldham Anal Chem 62 1990 625 Kinetic convolution This algorithm carries out kinetic convolution according to F E Woodard R D Goodin P J Kinlen Anal Chem 56 1984 1920 The number of operations is approximately proportional to the square of the number of points This convolution requires the value of the rate constant of irreversible homogeneous follow up reaction ECi mechanism 5 11 Convolution in practice The Convolution option can be selected for data measured with cyclic and linear sweep voltammetry This convolution menu offers a number of transformations of the data set like differentiation integration and convolutions There are three principal types of convolution available differintegration convolution with t function equivalent to fractional differentiation or integration d
27. checked the value of the ohmic drop is determined only Current range bipotentiostat CV CM The input parameter only appears when the Autolab is equipped with the bipotentiostat module The maximum range is 10 mA the minimum range is 100 nA 114 User Manual GPES for Windows Version 4 9 Cutoff on charge CM interval time gt 1 s If checked in chrono amperometry or coulometry the specified cutoff value is charge otherwise it is current This feature allows to specify a cutoff value for the charge in chrono amperometry Cutoff value CM interval time gt 1 s If the specified value is exceeded the measurements will proceed with the next potential level or if it is the last potential level in the sequence the measurements will stop Cutoff value for ge signal gt V CV and CM interval time gt 1s This value is the upper limit for the oe signal as soon as this limit is reached the experiment will stop Cutoff value for ge signal lt V CV and CM interval time gt 1s This value is the lower limit for the 2 signal as soon as the limit is reached the experiment will stop Cutoff value for time gt CM interval time gt 1s The measurement is aborted when the time exceeds the specified value It is only active when the option Specify time limit is checked Define potential w r t OCP CM If checked the stand by potential and the specified potential levels are applied with resp
28. cutoff value CM interval time gt 1s If checked and the specified cutoff value is exceeded the measurements will proceed with the next potential level or if it is the last potential level in the sequence the measurements will stop 122 User Manual GPES for Windows Version 4 9 Specify maximum dE di or dQ CM interval time gt 1s If checked a data point will not only be recorded after the specified interval time but also if the change in current charge or potential exceeds the specified value Specify minimum variation CM If checked this parameter can be used to stop a chrono amperometry or chrono potentiometry experiment as soon as the change in respectively current or potential is less than the Minimum variation value In other words as soon as the measured signal has reached the Minimum variation the experiment is stopped or the next step in the experiment is applied Specify Time limit CM interval time gt 1s If this option is checked the measurement will stop when the time exceeds the value specified for Cutoff value for time gt This option might be of use when a large number of cycles is specified Stand by potential All The potential which is applied after the measurement in case of cell on after measurement Sometimes CM ECD it is also the start potential before a measurement Start potential CV VA The potential at which the measurement a
29. memory Number of potential steps CM During the measurements the potential steps from the stand by potential to a number of potential levels These levels can be specified under header Potentials Number of pulses ECD The number potential levels which should be applied in multiple pulse or differential pulse mode Number of scans CV The number of cycles or linear sweeps to be measured Number of scans LSV staircase hydrodynamic The number of scans with a different rotation speed Number of scans VA The number of times a voltammogram is recorded The presented voltammogram is the average of all recorded voltammograms Phase VA ac voltammetry If Phase sensitive field above is checked the supplied value will be the phase shift with respect to the applied ac potential at which the ac current is obtained Phase sensitive VA ac voltammetry If checked a value for the phase should be supplied Potential bipotentiostat CV CM The input parameter only appears when the Autolab is equipped with the bipotentiostat module The constant potential which should be applied to the second working electrode Potential limit PSA The measurements will stop when the potential passes the specified potential limit Potential shift CV The specified amount will be added to the recorded potentials of the voltammogram In this way it is possible to record potential versus present reference electrode but display
30. modified value The modified value is accepted when a beep sounds The layout and setup of the Edit procedure window is more or less the same for all electrochemical methods For most methods on Page 1 the following type of parameters can be specified the first pre treatment and subsequent equilibration the definition of the type of measurement the potential or current level parameters the title and subtitle The items on page 2 depend on the method For voltammetric analysis the following extra items are available number of voltammetric scans which will be recorded subsequently and averaged a number of comment lines For cyclic and linear sweep voltammetry the following items are extra available extra pre treatment stages special measurement conditions special display option to swap x and y axis Tafel plot a number of comment lines current boundaries for reversing the scan direction optional chronoamperometric measurement conditions at the vertices optional recording of an external signal For the chronomethods the following extra items are available extra pre treatment stages special measurement conditions 64 User Manual GPES for Windows Version 4 9 optional recording of an extra signal a number of comment lines For electrochemical detection the following extra items are available extra pre treatment stages a number of comment lines differential pulse condition if applicable For potentiometric stripping analysi
31. pe deserve special attention They can be considered as respectively semi integration and semi differentiation Another reason for mentioning differintegration is that there are special algorithms allowing this operation to be performed rapidly For more information please refer to K B Oldham J Spanier The Fractional Calculus Academic Press N Y 1974 As mentioned before in case of semi infinite linear diffusion the results of convolution with the function t semi integration and semi differentiation are well defined and quite simple This suggests that these methods can be used for the investigation of variations of product concentration on the electrode surface as well as detection and studies of phenomena resulting in deviations from linear diffusion transport Other practical applications are the resolution of overlapping voltammetric peaks the determination of the formal potentials and numbers of electrons involved in the reaction step detection of the adsorption on the electrode as well as of the irreversible homogeneous reaction consuming the product generated by the electron transfer step Detection of overlapping peaks The nature of the voltammetric peak causes overlap in case of complex voltammograms While the ascending branch of the peak rises rapidly and the beginning of the rise can easily be found the descending branch follows a function and is characterised with a slow decrease Even far away from the top of
32. peak area can be determined Fig 46 Example of polynomial basecurve in peak Data presentation File Copy Plot Analysis Edit data DPASY of Cu Pb Cd and Zn in acetate buffer 0 0 500 0 400 0 300 E4W200 0 100 0 68 User Manual GPES for Windows Version 4 9 Furthermore it is also possible to draw a linear baseline in case only the front part or only the rear part of the baseline is known The options Lin front baseline or Lin rear baseline on the Baseline panel should then be checked Now two points on the front part respectively rear part of the peak should be marked In free cursor mode only a linear baseline can be drawn When the options Curve cursor linear baseline and Free cursor are selected baselines can be constructed manually After the first point of the baseline has been marked a line connected to this point will be dragged until a second marker is clicked The Set format button can be clicked to adjust the formats in the Set results format window The defaults in this window are the formats of the axis labels The results of the peak search are Position potential at which the current with respect to the baseline has a maximum Height maximum current with respect to baseline Fig 47 Example of a linear front baseline Data presentation Lox File Copy Plot Analysis Editdata DPASY of Cu Pb Cd and Zn 0 23x10 J dd in acetate buffer 0 20x1074 0 1
33. ratio product reactant Diffusion coefficients ratio Dp Dr ile Temperature K Fitting process is carried out until convergence criteria are satisfied or either the iteration limit or time limit is reached There are two types of convergence criteria based on x and related to the parameter value change Criteria based on x demand that 1 change of Y in the last iteration step must be negative x decreases 2 value of x weighted with should be less than 1 or less than Ly for 1 unweighted data 3 the last change in X is so small that it can be neglected The value that can be neglected is defined by the user as the maximal relative in x Option menu Fit control parameters The default maximal change is 0 01 1 of x value Criteria related to fitted parameters value require that the change to the parameter value in the last iteration should not exceed a certain value This value can be defined as an absolute or as a relative one a fraction of the parameter s value In the extended setup Option menu it is possible to define the value and the type absolute relative of the convergence criterion for each fitable parameters The 84 User Manual GPES for Windows Version 4 9 Convergence field contains the criterial value and the buttons right to the value field can be used to select the absolute type of the criterion the relative one or to disable the criterion for this parameter
34. the direction of the horizontal as well as the vertical axis It allows peaks always to be displayed upwards Enter text When this option is clicked the text Text field appears in the left top corner of the graph This text can be dragged over the graph After double clicking the text field the text itself and the format can be modified The first text line of the Paste buffer can be inserted on the text field as well Thus a line of text from the Analysis results window can be copied to the Paste buffer and subsequently inserted there Please note that the text cannot be stored Analysis The Analysis option contains an elaborate set of methods to extract essential parameters from the measured data The background is described in the special chapter about this subject The available data analysis options depend on the selected electrochemical method Edit data The Edit data option gives the opportunity to modify the presented data The backgrounds are explained in the special chapter about this subject Work scan The Work scan option which is only present for cyclic and linear sweep voltammetry allows the selection of a scan for further data analysis Work potential The Work potential option which is only present for multi mode electrochemical detection allows the selection of a potential for further data analysis and peak search Editing graphical items and viewing data Except for the available options items of the gr
35. the peak the F E Woodard R D Goodin P J Kinlen Anal Chem 56 1984 1920 J H Carney Anal Chem 47 1975 2267 Chapter 5 Editing of measured data 103 value of the current differs significantly from zero Due to this feature all following voltammetric peaks rise from the tail of the previous one If the separation of two voltammetric peaks is large enough they can be detected without any problems The situation is difficult when the distance between peaks gets smaller below a certain distance the first peak is reduced to a shoulder on the rising part of the next peak The extreme situation is shown in fig 56 C where the overlap is very strong so that only one peak can be observed and there is no indication for the presence of more of them Fig 54 Overlapping linear voltammetric peaks and their semi derivatives In most situations except in those of extreme overlap semi derivative peaks are clearly visible and their number can easily be found There are however three important limitations to this method First voltammograms that are to be semi differentiated should be background corrected semi differentiation changes a constant or a linear background into complicated forms in the semi derivative domain 104 User Manual GPES for Windows Version 4 9 Secondly semi derivative peak artefacts have to be recognised consider the case of an uncomplicated slow electron transfer leading to the voltamm
36. them with respect to another Appendix II Definition of procedure parameters 119 Potentials CM A table of potential levels can be specified The number of rows is equal to the number of potential levels specified on the field above During a measurement sequence the potential steps from the stand by potential to each of the specified levels The following columns can be specified in the potential table Potential the required potential level Duration the time the potential level is applied Sample time the time between two current samples This column is only present for the chronomethod with interval times lt 1s See description of the methods Potentials table ECD In this table the potential levels to be applied and their duration can be specified in multiple pulse or differential pulse mode The number of rows is equal to the Number of pulses In multiple pulse mode in a third column it can be specified whether the current should be recorded or not In differential pulse mode the two levels specified on page 2 are recorded Pulse time VA Normal pulse Time during which the potential pulse is applied Purge time All The time the gas valve is positioned to flow the gas through the cell This parameter only appears when an automatic electrode is present see Hardware configuration program Quick save of previous scan CV When more then one scan is recorded in Cyclic voltammetry it is possible t
37. this current range during execution of the current procedure The response times of this current range is too high for the specified measurement procedure Settings In the Settings panel the mode of operation can be defined The text on the button represents the current situation The following buttons might appear depending on the type of potentiostat galvanostat Cell on off allows to switch cell on or off In the off position the connection of the potentiostat with the potentiostat galvanostat is broken so no current can flow between the counter and working electrode High Sens off on it indicates whether the gain 100 of the amplifier of the AD converter is used If off only gain 1 and 10 are used The current resolution is improved by a factor of 10 The disadvantage of the high sensitivity on is that the measurements are somewhat slower and that they are more susceptible to overloads It is recommended to switch the high sensitivity on only when the limits of the digital resolution show For example at the current range 100nA the current resolution is improved from 3pA to 0 3 pA when high sensitivity is switched on See also the chapter about the digital base of Autolab in the Installation and Diagnostics guide High Stability High Speed The potentiostats galvanostats can be used in either the high speed with high bandwidth mode or the high stability with low bandwidth mode The bandwidth at high stability is about
38. this value during your measurements Fig 14 Effect of overcompensation of the iR drop GPES Manager Oo x File Method Utilities Options Project Window Help AE ef ul al 418 18 Woltammetric analysis Differential Pulse Procedure DEMOEAQ1 R Compensation Positive Feedback Potential pulse 001 2 5V 1 Positive feedback Duration 003 3 5 01 F Switch iR compensation off at current overload Ru 97 7 Ohm 0 050x1074 0 050x107 0 100x1074 0 150x1074 0 200x107 0 i Messages Z HA Start A Exploring P Bl ares Mana Cl Manual control UL Data pres El Edit procedure ES Paint Shop Prol 11 47 AM 2 10 Detection of noise problems In the GPES software an option is available to detect noise problems Since noise is encountered frequently in electrochemical research it is useful to become familiar with the detection of problems caused by noise In GPES the Check Cell option under the Utilities menu provides the option to detect noise Chapter 2 Getting started with GPES 25 Please connect the red banana plug to the WE c connection on the dummy cell In order to generate some noise please connect an unshielded cable between the blue banana plug and the RE connector on the dummy cell and place part of this unshielded cable over the monitor of your computer In manual control please check the 100 nA Current range ch
39. to control the multichannel potentiostat with GPES Activate the multichannel option by starting GPES with the shortcut Multichannel GPES The multichannel software is similar to the GPES software however some options are different or not available The differences are explained in this paragraph Installation and test The Hardware Setup program contains a button for Multichannel setup After pressing this button the following screen appears Fig 59 Multichannel configuration Multichannel configuration Number of channels 102030405 6 Type of extra channels ARRAY PSTAT1O i Independent current ranging x Offset DACs present Minumum threshold current 4 0 The items above are factory settings and should normally not be changed The test of the software is similar to the test of GPES The procedure TESTCV6 can be used for more than one potentiostat If the multichannel system is equipped with ARRAY modules one dummy cell is available After loading the procedure TESTCV6 from the AUTOLAB TESTDATA directory the Multi channel control window shows that PGSTAT and ARRAY 2 are active Now connect the dummy cell The lead from ARRAY 2 should be connected to WE b After starting the execution of the procedure the normal dummy cell response should appear and the current response should be the same for both channels In a subsequent measurement ARRAY 3 can be connected to the dummy cell in stead of ARRAY
40. using the Work scan option 7 You are able to change some measurement parameters during the measurement by using the Send option in the Edit procedure window Please re start a measurement with 100 scans and during the measurement change the Scan rate from 0 1 V s to 1 V s After clicking Send the speed of the measurement will increase You can again stop the measurement by using the Esc button 12 User Manual GPES for Windows Version 4 9 Fig 4 Edit procedure window A Edit procedure send Page 1 Pretreatment First conditioning potential V Duration s Equilibration time s Measurement Number of scans Cell off after measurement Standby potential V Potentials Define start potential w r t OCP Start potential V First vertex potential V 6 Second vertex potential V 4 Step potential V 00244 Scan rate V s 099992 Chapter 2 Getting started with GPES 13 8 After finishing a measurement the program allows you to save more than one scan by selecting Save scan and then selecting a scan that you would like to save For the following scans you want to save please select Save scan as The Save data buffer option saves all the scans that the PC has in its memory 2 2 The use of the Manual control window Fig 5 Manual control window the appearance depends on the Autolab configuration
41. voltammograms or convoluted voltammograms see Convolution option After having selected this option the user is asked to define a base line and a limiting line Subsequently Ey is calculated from the crossing between the average line of the base line and the limiting line with the measured curve The limiting current at Ey is calculated as two times the current at Ey with respect to the base current After pressing the Continue button on the Wave log analysis window a Tafel line analysis can be done from the plot of In id i i versus the potential where i stands for current id for limiting current and In for natural logarithm If a cyclic voltammogram has been deconvoluted the i is replaced by m The markers for the line should be selected not too far from zero on the Y axis The intercept is at E 0 The parameter Alpha n An has been calculated from the slope Chapter 4 Analysis of measured data 71 slope onF RT F Faraday constant 96484 6 C mol R Gas constant 8 31441 J mol K T temperature 298 15 at 25 C n no of transferred electrons a 1 for reversible reactions amp transfer coefficient for irreversible reactions An example of wave log analysis is described in Chapter Getting started with GPES 4 7 Tafel slope analysis This option is only available for Cyclic and Linear sweep voltammetry When the option is selected the current is plotted on a logarithmic scale The user is aske
42. 00 V 100 Y 5 000 Vv 050 v 100 V 050 Vv When this window is behind other windows on the screen it can be shown with the Window option from the GPES manager The last item is Multichannel After clicking this item the multichannel window will be shown Depending on the configuration this screen will be adjusted The base potential for all arrays including the PGSTAT can be set in the PGSTAT panel If offset DAC s are present a specified offset potential can be given With Dependent current ranging the current range of all channels will be the same Changing the current range of Array 4 will lead to a current range change of all channels The Active option button allows to select the channels that should be measured Note that the potential will always be applied to all channels The number of items on the Manual control window is considerably reduced compared to normal GPES On the Data presentation window two additional items are present 1 The Signal menu allows to select the signal from which channel is the active work signal All Edit and Analysis operation will be performed on this signal The currently selected signal is shown between brackets 2 The Plot overlay signal option in the Plot menu allows to overlay several signals It operates similarly to the other overlay options The following methods are available in the multichannel mode Voltammetric analysis Dif
43. 02x10 seme i hi i Ht ii i Wl kyi phe H 0 2999x10 4 0 2998x10 4 0 2997x10 0 2996K10 5 42 User Manual GPES for Windows Version 4 9 The measured current and the five average values over one power cycle normally 0 020 second are plotted in the Measure window The obtained five average values and their standard deviations are given in the Check cell window A judgement about the noise level and the selected current range are given See also Chapter 16 of the Installation and Diagnostics guide It is possible after an improvement of e g the cell configuration to re Measure By pressing Cancel the Check cell window disappears Plate The Plate option will display a window in which three plating potentials a cell off wait time and a final potential can be specified Fig 25 The Plate window Plating parameters First Final Potential 0 1 Y Potential 0 4 Y Time 10 S Time 40 S Second Wait time Potential 0 2 Y With cell off 5 S Time 20 S Third Confirmation Potential 0 3 Vv Time 0 s The three plating potentials are alternated with the cell off time Subsequently the final potential is applied Sleep mode When the Sleep mode option is clicked newly measured data will no longer be displayed in the Manual control window and the Data presentation window This option is useful when during
44. 0nAtolA in nine ranges 0 2 of current and 0 2 of current range 0 015 of current range 0 0003 of current range 30 fA gt 1 MHz lt 250 ns with external source high speed high stability gt 1 TQ lt 8 pF lt 1lpA gt 4 MHz depending on selected range 0Q 20Q at 1 A range to 0Q 200 MQ at 10 nA range current interrupt and positive feedback available 0 025 yes potential and current potential current and optionally charge yes multipleWE option 133 Autolab with PGSTAT100 250 mA 100V yes yes 10V 0 2 of setting 2mV 150 uV 300 or 30 uV 10 nA to 100 mA in eight ranges 0 2 of current and 0 2 of current range 0 015 of current range 0 0003 of current range 30 fA 500 kHz lt 500 ns high speed high stability gt 100 GQ lt 8 pF lt 1pA gt 4 MHz depending on selected range 0Q 200Q at 100 mA range to 0Q 200 MQ at 10 nA range current interrupt and positive feedback available 0 025 yes potential and current potential current and optionally charge yes no 134 User Manual booster option analog integrator time constants interfacing A D converter auxiliary input channels D A converter auxiliary output channel digital I O lines WxDxH weight power requirements pAutolab type III no yes 10 and 100 ms land 10s USB 16 bit with software programmable gains of 1 10 and 100 1 16 bit t
45. 10 kHz Some electrochemical cells may cause stability problems with the instrument in high speed mode Especially cells with high capacity and low resistance may cause oscillations Using the instrument in high stability mode may prevent oscillations It is advised to use high stability in all experiments except when high bandwidth is needed High speed or high bandwidth is needed when frequencies higher than 10 kHz or sampling or interval times below 100 us are used Potentiostat Galvanostat allows switching from potentiostatic to galvanostatic mode It is highly recommended to switch the cell off before the mode change In case of potentiostatic control the output of the DAC module corresponds to an applied potential level In case of galvanostatic control the output of the DAC module corresponds to an applied current Chapter 3 The GPES windows 55 iR comp on off switches iR compensation on or off A more elaborate description is found in the dedicated paragraph in this chapter only available with a PGSTAT12 20 30 100 Potential The Potential panel contains a slider and a text box With these tools the applied potential can be specified The slider box can be dragged to change the value A click on the arrows and slider bar changes the value by a distinct increment The increment is different for the arrows and for the bar In the two panels below the measured current potential and or time can be displayed depending on t
46. 2 After ARRAY 2 has been made inactive and ARRAY 3 active the same current response is expected In this way all channels can be checked In case of a multi PGSTAT10 set up two dummy cells should be available The PGSTAT10 2 should be connected to the second dummy cell Then the same procedure should be followed as for the multi ARRAY set up as described above The DIAGNOST test is available but does not work properly The zero test of the ADC does not work properly because the test channel is used for one of the extra channels 130 User Manual GPES for Windows Version 4 9 Program operation After starting the program an extra Window appears Fig 60 Multi channel control window la Multi channel control x PGSTAT10 ARRAY 2 ARRAY 3 ARRAY 4 TARRAY 5 ARRAY 6 Active X Active X Active IK Active IK Active i Active l 000 pA l D00 pA 00 mA l 00 mA l 000 pA l 02 mA E 000 Y E 001 Y le 001 Y E 170 Y E 001 Y E 001 Y 0 PF10mA OT 10mA Xx 10mA K10mA OT 10mA K10mA OT 1imA OTimA OT imA OT imA OT imA OT imA O 100uA PM 100 uA Of 100uA FP 100 uA Of 100uA O fF 100 uA OF 10ud OT 10uA OF 10uA FIDA OF 10uA OF 10uA Ok 1A h1uA Of iu T1uA kid Of 1uA O 100nA OF 100nA F 100 nA F 100nA O F 100 nA O F 100nA Base potential Offset potential Offset potential Offset potential Offset potential Offset potential dd O Bid O AAA Bid O bli LA Bild EJ Bl 0
47. 2 mac present in the AUTOLAB TESTDATA folder Project wizard The Project wizard provides an easy way of editing and or defining a project This option allows the user to pick project command lines from a list of all commands insert them in a project and define the parameters The window below gives a project Wizard overview 48 User Manual GPES for Windows Version 4 9 Fig 26 An example of a project inside the Project wizard GPES C Autolab TestD ata Demo01 Je x Category Command aise Delete lt lt SSS SS SS SSS SS ed This a demonstration project The project executes a number of procedures and determines the minimum and maximum value in a data set If you have installed the Autolab application programs in another directory than C AUTOLAB you have to change the path in the ProcedurelOpen DataSet SaveAs and DataSet Open command lines Please connect the dummy cell using WE a AddT oPotlevel The analysis results are printed in the Analysis results window a E Clear the Analysis results window y Results clear Use method voltammetric analysis ProcedurelMethod VA Load procedure TESTSDC Sampled DC voltammetry from the testdata directory Procedure Open C SUTOLAB TESTDATAATESTSDC Start execution of the procedure ProcedurelStart Store the data in the file TESTSDC in the data directory DataSetiSave s C AUTOLAB DATAXTESTSDC Determine the minimum and m
48. 42 5 R Greef R Peat L M Peter D Pletcher and J Robinson Instrumental Methods in Electrochemistry Ellis Horwood Limited ISBN 0 13 472093 8 7 Chapter 2 Getting started with GPES 9 2 Getting started with GPES In this chapter some basic examples are given to become familiar with GPES The possibilities and the options of the software are described Some of the examples contain a measurement with the Autolab dummy cell so before you start with the first example please connect the dummy cell box to the cell cable by putting the banana plug connector into the matching colour connector on the dummy cell The red banana plug should be connected to WE a As soon as you start GPES by clicking the icon in the Autolab application window you will see the standard layout of the GPES software which consists of three windows and two bars Fig 1 Default layout of GPES windows GPES Manager Manual control File Method Utilities Options Project Window Help AE o z gt ul 2 418 2 Cyclic voltammetry staircase Normal Procedure DEFAULT Aa Edit procedure Manual control Send Current range Settings Potential iR compensation Page 1 Oia Cell off gt O F100mA Pretreatment O K10mA High Sens off Kim First conditioning potential V O PE 100uA High Stability Integrator Duration s O R 10uA Current O001s Equilibration time s O 1A Potentiostat O Potential Olis OF 100nA Ols Measurement
49. 8x1074 0 15x107 4 0 13x107 4 JA 0 10x1074 0 08x107 4 0 051074 0 03x1074 Peak area area of the peak corrected for the baseline For data from cyclic linear sweep voltammetry the area is expressed in Coulombs This means that the area is divided by the scanrate Derivative the sum of the absolute values of the maximum and the minimum in the derivative of peak Ep Ep 2 the difference between peak potential and the potential at half height This value is only printed for data from cyclic and linear sweep voltammetry It is useful to derive kinetic parameters See the book of C M A Brett and A M O Oliveira Brett Electrochemistry Oxford science publications ISBN 0 19 855388 9 Chapter 4 Analysis of measured data 69 In quantitative voltammetric practice the peak height is the most widely used parameter to determine concentrations The peak area is less sensitive to noise but if the peak is not completely isolated from another peak the error in the peak area will be high The sum of the derivatives of the peak is less sensitive to peak overlap However derivation of an experimental curve will increase noise For more details see Ref J Tacussel P Lectere and J J Fombon J Electroanal Chem 214 1986 79 94 4 2 Chronoamperometric plot The Chronoamperometric plot option produces a special plot for two sequential potential steps in a chronoamperometric experiment The first step should be the for
50. IMUM cccccccccseseesecessscsesceccscsccessecesseccessscsessscsusssecssscssssceessecesssseesseceessess 74 4 11 INTERPOLATE 4 12 TRANSITION TIME ANALYSIS ta Atala 413 ETE AND SIMULATION a a de id eee tak The simulation method cccccccccccsscesccsccscenessecseesseeseesecnsceseeceeaeeaeeneeneeens The fitting Method asa Elements of the Fit and Simulation Window Fitting and simulation step Dy Step cccccccccccesscesscesseseseeseceeseeseceseecseeeseecaeecseeeaceseeeaeeescessaeseneseaeensensaeeags ittin in MOTE detail mi ee Ae reat A OAS da ean haha 4 15 WE2 VERSUS WE PLOT 4 16 ENDPOINT COULOMETRIC TITRATION ccsccessesseceeceseeeseceseecseecaeecaeecuaeeueceaeenseceaeenseeeseeseenseeeeeess 95 5 EDITING OF MEASURED DATA 5 1 SMOOTH cooccccccononncninnnnos 5 2 CHANGE ALL POINTS 5 9 DELETE POTS aa is 9 4 BASELINE CORRECTION AA ae Aeon did 5 5 UBTRA CDI e dl oie 5 6 SUBTRACTION OF SECOND SIGNAL FROM FIRST SIGNAL ccccccsccecceesssseccesssccseceessceecccssssteeeeeesseeeeess 99 DP DERIVATIVE adn INTEGRA TE oo 5 9 FOURIER TRANSFORM sz cc s ssssu ss talas i nn tao iii irse 5 1 OSCONVOLUTION TECONIQUES tes Detection of overlapping PeaKS csccccccascccusicsscecsscnsceincavssveavancacenceuea sages ceberaclaveanaa ceuedanaccveanssveessdeea ees Determination of formal potential and the number of electrons involved s Irreversible homogeneous reaction consuming the product of the electrode process Inve
51. Linear sweep segment Staircase sweep is disabled Potential V Step segment Sample time s Step segment the lowest possible value is 0 0002 s Total time s Step segment End potential V Sweep segment Scan rate V s Sweep segment the highest possible value is 5000 times the step potential value Step potential V Sweep segment The parameters for the Step segments are similar to the chrono methods with short interval times see items Potentials in the appendix The parameters for the Sweep segment are similar to the parameters for Linear sweep voltammetry Stirrer off during conditioning VA Switch off the stirrer of the Automatic electrode during the conditioning stage Stirrer off during deposition VA Switch off the stirrer of the Automatic electrode during the deposition stage Stop Equilibrium at threshold VA CV CM ECD Enable the option to abort the equilibration stage when the Equilibration threshold level is reached Stop scan CV linear sweep The recording of the sweep will be terminated if the current exceeds the upper or lower specified limit 124 User Manual GPES for Windows Version 4 9 Surface area cm 2 CV 8 CM Surface area of the working electrode with which the Current density can be calculated in the Analysis menu of the Data presentation window Switch cell off when i 0 A CM interval time lt l s If this option is checked the cell will be switched off during lev
52. Noise 3 steel rods in KCI solution Frequency Analysis Window Function Result Type oK O None Elf and f O Bartlett ozi Cancel Hanning O Hamming 200 Black Time s AR P Substract Offset Da Messages Zz MStart Exploring Psp Q Exploring gp B GPES Manag amp Manual control SLEdit procedure Ae Data presenta Paint Shop 12 09 PM Disk file Analysis Spectral noise 2 9 iR compensation When your Autolab is equipped with a PGSTAT12 20 30 100 you are able to measure the uncompensated resistance in your electrochemical cell and to compensate for this resistance The GPES software provides two methods to do this iR Interrupt and Positive feedback see Chapter 3 for more details This example is meant to make you more familiar with both options Before starting please connect the WE connector of the cell cable to WE c on the dummy cell T interrupt a Under the Utilities option in the GPES window please choose I interrupt the iR compensation window will appear In the manual control window please type 1 0 V in the potential panel and check the 1 mA Current range checkbox You can now switch the cell on by clicking the button in manual control b In the iR compensation window please give the following values Range 10V Duration of interrupt 0 001 s First marker 15 Second marker 35 The current will now be interrupted
53. Normalised electron transfer rate at E 0 log k 4 exchanged electrons transfer coefficient an limiting current Jim A constant background current A Initial guesses available for log k E It an EE Thorm background current fh Comments There is no need to set the number of exchanged electrons because the term on is fitted as a whole The theoretical expression for the limiting current at a large flat electrode is lim nFA Coul DIT 2 where tp is the pulse time The characteristic potential E is defined as E RT anF Ink y E RT anF Ink where kj k t D and k k t D ks and km are the electron transfer rates used in Butler Volmer equation I k cp exp onF RT E k c exp onF RT E E Normal pulse voltammetry reversible electrode process followed by irreversible chemical reaction ECi Reaction equation REE P ls B Fitable parameters redox potential E V forward chemical reaction rate kc foll gt norm Es limiting current lim A constant background current A Initial guesses available for number of exchanged electrons E Inorm background current Chapter 4 Analysis of measured data 91 Comments The theoretical expression for the limiting current at a large flat electrode is iim nFACbuk D Ttp where ty is the pulse time The forward chemical reaction rate is normalised with respect to the time scale of the experiment ky k tp Normal pulse voltammetry reversible
54. O SetBit P1 An a ON On connector Pl port A Pin number 5 pin number 1 has value 0 is set ON i e sends a trigger DIO SetBIt TEL AY 14 QEF On connector Pl port A Pin number 5 is set OFF again DIO SetMode P1 A IN On connector Pl port A the mode is set to IN so ready to receive a trigger DIO WaitBit P1 A 2 ON The project will wait for an input trigger on Pl port A Pin number 3 DIO SetMode P1 A OUT On connector Pl port A the mode is set to OUT so ready to send a trigger DIO SetByte P1 A 3 On Pl port A both pin 1 2 0 and 2 2 1 are set ON In case one wants to set Pin 3 and 5 one needs to set the value 40 2 34 2 5 instead of 3 DIO SetMode P1 A IN On connector Pl port A the mode is set to IN so ready to receive a trigger DIO WaitByte P1 A 3 On Pl port A the project is waiting for an input trigger on both pin 1 and 2 In case one wants to receive the trigger on Pin 4 and 6 one needs to set the value 80 2 4 2 6 instead of 3 Fig 26a Schematic overview of both DIO ports with PIN numbering for the different sections Pin 25 is always the digital ground Port Port 2 cn ec e Sect E LOWER 20 90 O ge os Oe Se ee Section A O Section B i 1 o Section c UPPER O 30 OS 190 25 dgnd Le Section C LOWER joe o O O CONoOaRWNMN BRWPY Se
55. OT 10nA iB comp off 10s Number of scans O Time Integrator off Filter ECD off y Potential Of Ols kesr Remote Cell off after measurement Cis OSs E noise O PE Standby potential V Data presentation Potentials File Copy Plot Analysis Editdata Work scan Define start potential w r t OCP Ferri Ferro Start potential V 398 Cyclic voltammetry First vertex potential V 6 Second vertex potential V 4 ss Step potential V 00244 e aik Scan rate V s 099992 0 0 100x10 0 200x10 0 300x10 0 5 o E V 0250 0 400x10 0 300x10 0 200x10 Title and subtitle Ferri Ferro zl E 005V 1 00A AStart X Exploring EJPaint Shop I Screen Cap B GPES Ma 1 Edit proced 1 Manual con e Data prese T 3 39 PM im Messages Manual control The two bars are The GPES manager bar with the menus and the tool buttons The Status bar at the bottom of the screen which contains the start and stop buttons for measurement and displays the system messages 10 User Manual GPES for Windows Version 4 9 The three windows are The Edit procedure window which specifies all the experimental parameters Changed parameters are automatically saved when leaving the software and will appear as default parameters on the next occasion For most of the techniques this window wi
56. SS 64 117 DIO Ports knnt ione ei a E E E E A E E E E Ri 49 UGE Vis Plte direne a o ha 59 E A E AEE 59 138 User Manual GPES for Windows Version 4 9 Edit POEMA A AR AA che 32 63 electrochemical detection occcoooccnnncnnnnccnnnnnnnccnnonanocnnonanocononnnocononnnociconanaros 5 47 60 Electrode control ri dd di rot da 33 ENtETtX Ed eins 60 A cee eh atte RR 31 Export Chrono data AA A A ia 30 Exp rtdata buffer casos sxseecssscnceasveras sos dosesceencpaaedonsnueasiadieds cauatansensagaccedeseat 30 Export to BAS DigiSim data c ccccccceccsesseneceeceeeeeeneaeeeeceeeeesneeeeeeeeeesnenaeeeeeeeeseaneas 30 F 1 A oe eee TA Ol EA EEN AA oi ibas 73 97 Filt t fOr devat VE ANS PON PO O E cea Bs foe ee as 96 First and SECOnd A tt A a de 59 10 Ge Pe en NN 74 MARS ranen hes ee A ad ate ela Petia ee a oie 67 68 FPEQUENCY PEC A dod ebnia pies Dene to 73 G CalVanOStat ex rivessitet A ed heh ts de sek tet dea thea seg 5 6 30 OPES MES unid e dada 28 PESTE a A A A A A 28 APM A A A toes Al Ideas 5 6 27 63 H A rrr went cer rere ever re Pere rere re see reece erence rere 5 7 52 63 112 High Sensitivity ces sra ti ilatina 54 I TOISK yon oct ni A A E nl 95 TEME A A betes oa Ree ea ae ope eas 37 ANE STALE es cet os enh TEA E E E NAT 99 NA 53 56 TInt p Ol Ate nn A Ad tt 74 EREI O NN 110 IRE COMPAS ton a ds A EKE RAE e E ad alas 37 39 55 TPIT ace RES a aiee 95 L linear Te EM tai Igea 69 70 74 linear sweep VO taMMEe
57. Start button has been pressed If the corresponding Duration is zero the potential is not applied First potential boundary CV Used in combination with Second potential boundary for automatic calculation of the total positive and total negative charge Only active when Use boundaries for Q Q calc is checked In galvanostatic cyclic voltammetry or galvanostatic chronopotentiometry potential should be read as current and vice versa 116 User Manual GPES for Windows Version 4 9 First vertex potential CV cyclic The potential goes from the start potential to the first vertex potential where it turns around to go to the second vertex potential Frequency VA The number of times the square wave or sine wave perturbation is applied per second in respectively square wave voltammetry and ac voltammetry Highest current range bipotentiostat CV CM The input parameter only appears when the Autolab is equipped with the bi potentiostat module The maximum range is 10 mA the minimum range is 100 nA The actual current range for the bi potentiostat module will be automatically set between the specified highest and lowest current range Initial rotation speed rpm LSV staircase hydrodynamic The rotation speed applied during the first scan Interval time CM interval time gt 1 s Normally the time between two recorded data points If a maximum dE di or dQ value is specifie
58. THE GPES WINDOWG scccccscsssssssssssssssssessessecsssesscsssssssassssessssesessessesssssssssssssssessessasessessessssoses 27 3 1 GPES MANAGER WINDOW cccsessesssecseccccccssccsceesssssssssssecccccssssssseeuseussssseecssseccesssseseuusseessesssesceesess 27 File Mena ata ata its 27 Method OT LTLT eds AL esis rsen RES OA RAN Options Window SZ STATUS BAR a E AA AAA AA AAA 3 3 MANUAL CONTROL WINDOW CUT T ETE PANG ei A A e E SENS ida Potential Noise meters LR COMPCNSQUION AA cess hei lete ee BA keto as INCL li idad Filter panel 3 4 DATA PRESENTATION WINDOW E RS NT NARA E A O E OO WOK SCN inea da tee Work potential Editing graphical items and viewing data 3 5 EDIT PROCEDURE WINDOW 0ccceeseees 3 6 ANALYSIS RESULTS WINDOW 4 ANALYSIS OF MEASURED DATA occnconicconoononconoononconcononconnononcnnonoonononconcononconcononconnononnoronosnososs 65 4 1 PEAK SEARCH 4 2 CHRONOAMPEROMETRIC PLOT 4 3 CHRONOCQULOMETRIG PLOT siirtona eE EEE E eE E RE E ERE T ss eedsusdsvanageptadeesvaceses 69 4 4 ICINEAR REGRESSION ctra ra 69 4 5 INTEGRATE BETWEEN MARKERS sscccssscessceescecesseeceseecesacecsececeeacecesaeceaceeeeaecesseecesaeecseeceeaeeeseeeess 70 2 User Manual GPES for Windows Version 4 9 46 WAVE LOG ANALYSIS ut aia 70 AS TAFE SLOPE ANA aa 71 4 8 CORROSION RATE 4 ISPECTRAL NOISE ANA LY SIS 205557 c5s56 da does E 73 4 10 FIND MINIMUM AND MAX
59. Table of contents 1 Table of contents TABLE OF CONTENTS oconocconcononconcononnoncononncnoncononconcononconcononconconcnnonon ono nonconcononcon canon con cono roronconosnonos 1 1 PRINCIPLES OF OPERATION ecccccconconncononnnonnonnonanononancnnonacononononncnnonoconcnnncononacon conca a corona con ccnconocinos 5 LA PREFACE A A EZ 5 1 2 THECONCE PT o eat Ae lost do e td ld edo lo O AA 6 2 GETTING STARTED WITH GPES oovccconicconoononoonoononconcononocnnonononnonoonosnonconcononconccnonocnnonoorononoonosnonos 9 2 1 RECORDING A CYCLIC VOLTAMMOGRAM WITH THE DUMMY CELL occoooooccncnooonnnnnnonnnnnnnnonnnnnnnnanonnninnno 10 2 2 THE USE OF THE MANUAL CONTROL WINDOW cssccccssssseceessessseeecesssneceeseneeeeeeeesaeeeeeessaeeesseeseeeeess 13 2 3 DATA MANIPULATION OF A CYCLIC VOLTAMMOGRAM ccccssesssceeeeesseeeeseseeeeecessaeeeeessnaeeesseeseeeenss 14 2 4 CALCULATION OF A CORROSION RATE c sccssccscssccsseesecsanceetnccsenecectaresensecersscsenedseunseesbeaceeoceseecevnanascens 17 2 5 NOISE REDUCTION 34 5 ovciviecvevesnscecusananevescscavenseasencauses EEEE E SE IAE E EEEE VISAS INE 19 2 6 DATA ANALYSIS WITH CHRONO AMPEROMETRY ssssccsssecesseceeseeccsseeesssecesseeeessscceseecesaeeeeseeeesseesens 20 2 8 ANALYSIS OF ELECTRO CHEMICAL NOISE 2 9 IR COMPENSATION csscccesseeeeeeeeteeeesees 2 10 DETECTION OF NOISE PROBLEMS cccccccessssceceessscececsssseeeessesseeeccsssaueceesenseeeeeeesaeeeesessaeessseeaeeeeeess 3
60. The fitting process finishes when all the convergence criteria are satisfied If the convergence is not reached in spite of many interactions done this can be due to the following reasons 1 Demanded precision of the parameters is unrealistic The level of noise in the data or precision of the measured variable usually current may keep the variation of the parameter of interest above the demanded level 2 The type of the criterion is not appropriate For example in datasets where the background is very small it is better to use the absolute criterion than the relative one for background value and relate it to the measured peak or wave current The model is not applicable In this situation the value of x is usually larger than 1 or larger than bd y for unweighted data while all other criteria can be met It is then advisable to either change the model of re examine settings for non fitable parameters like the number of electrons involved in the electrode reaction Finding interdependence of fitted parameters Dependence of parameters can be detected by inspection of the covariance matrix Covariance matrix in the Option menu or Ctrl M The diagonal terms are unity If a term corresponding to a pair of parameters is significant there is a serious chance that these two parameters are interdependent Problems can arise if two or more parameters are interdependent The matrices used during fit can become singular and an error occurs A
61. This option is only available for cyclic voltammetry It allows to store the chrono amperometric data which are recorded at the vertex potential See the input parameters under the heading Chrono amperometry in the Edit procedure window Export to BAS DigiSim data This option is only available for cyclic voltammetry Save the current active in such a format that it can be read by the program DigiSim This is an ASCII file with the default extension TXT Export data buffer to text file This option can only be selected for cyclic and linear sweep voltammetry As in the previous option the whole data memory is stored on disk but in this case in a readable ASCU format The file consists of several columns The first column is the potential or current in galvanostat mode and the other columns are the measured currents for subsequent scans potentials in galvanostat mode The first row indicates the scan number The separator c q delimiter between two columns is a TAB character The default extension of the file is TXT They are meant to be read by MS Excel they cannot be read by GPES In order to create a nice and properly columned file each scan should have the same number of points This means that the Reverse button should not have been clicked Also an interruption of a scan by pressing ESC should be avoided Chapter 3 The GPES windows 31 The layout of the text file saved with the Export data buffer to text file also contains
62. a 0 25 0 50 0 75 1 00 1 25 E V Zz Status Messages Disk file Q 1 515E 09 C Q 1 256E 10 C Edit data Smooth EH Start E Exploring Psp E GPES Manager E Manual control i Edit procedure be Data present a Paint Shop Pro 5 11 25 AM 2 6 Data analysis with Chrono amperometry From the Method menu on the GPES manager bar choose Chrono amperometry interval time lt 0 1 s 1 Load the datafile democx01 from the autolab testdata directory 2 The curve shown is the result of a double potential step experiment To do data analysis it is more convenient to choose just one of both potential levels at a time To do so from the Plot menu in the Data presentation window choose select potential and select the 0 7 V level The data shown now are the result of the selected potential step 3 In Chrono amperometry the current is proportional to 1 Square root of time In order to visualise this please double click the horizontal axis and change the scale to 1 square root The curve is now linear From the Analysis menu choose Linear regression and set two markers for the beginning and the end of the linear regression The Linear regression window now gives you the results From the slope of this line 1t is possible to calculate for example the diffusion coefficient Chapter 2 Getting started with GPES 21 Fig 11 Transition time analysis GPES Manager Manual control Oo x Fi
63. aa eE EK aE EE ERAR L chad eee Ere RENE EES o eraa ERENS 48 Project Wizarda enn ap ee iae yb ghee eae deat E EE pe eek E P EEEE 47 PAPH anio A A eee A rae he dt 95 Q Quel ET TASE EE E A Steen eer 57 R A OO 35 Rescale after Measurement oiiire tt ieee a AE Ea oe e EETA E nc nnnnnnccnnn anos 52 Rescale during measurement ocooooccnonoconccnonononcnnonancnnnnnnnnnononnononnnnnncnnnnnnncnnannnccnnnncanos 52 O 59 60 Reverse AXES ci r ites n Date anaE ins A sap cesslasl Gnade E REEE 60 S SE T A A A E AS ESA E 29 30 57 SAVE PLOCE UTE ind ri 28 Save procedure ashoot edre a ea a r ins E T EA ease EE EERE eS 28 E RCN 29 ICAA O iii it 118 SCNRIGA nanie ot 36 140 User Manual GPES for Windows Version 4 9 second sigala snssseversncncecasarsssacceeceses 55 59 65 113 119 121 EEN WI les le 59 110 Show all GPES files in File dialog bDOX oonnnocccnnnococcnococcccnnononcconnonnncnonnn cnc nannnnccnnnos 52 ShowW L back Ward esos talleres inde EEE bd ed 59 Show I POL Ward aa cicle ii idos 59 SIMULA A AA AAA A li 74 NES ossed eases cela vtiadesuesedevensd cabins ns rapeveatenebi ERAR ii iih 42 SIMOOUN ces4 staid schveodoostescete ct ineccandscsel EEE E EA E EE ER 44 97 99 A NE 121 Spectral Noiseanal a e a toveaeneeees a a levee aed ine 73 Squire WAVE annissa ies eN e aE EE EE OOE EE E T GEE AE EE RS 113 116 Start DUON meermin eante EE ESEE EAEE EO EE A ROE EEO OaE r ERESSE ORRE 53 stationary CUTTENL ccicioocacancnocodonacinanaiioncoinonod
64. ace Such conditions can be called mixed linear diffusion kinetic effects For a long electrolysis time the kinetic increase of the flux can entirely Chapter 5 Editing of measured data 107 compensate the decrease of the concentration gradient and may lead to steady state conditions provided that the amount of compound involved in reagent production is present in large excess Another type of effect can be observed when the solution is present in the form of a thin layer Electrolysis under such circumstances first leads to the depletion of this layer and then to the exhaustion of the entire solution volume This effect can relatively easily be observed in case of the dissolution of metals from a small amalgam drop or from amalgam film electrodes the process is initially controlled by linear diffusion but after some time the drop is depleted and the flux of the substance through the electrode surface drops more rapidly than 1 This is called limited diffusion An extreme case of this situation is the reaction of a substance adsorbed on the electrode or forming a monolayer on its surface In such a case no transport is needed and the whole amount of substance reacts within a very short time The measured current drops sharply to zero after exhaustion of the compound Cyclic chronoamperometry and chronocoulometry If an electroactive compound reaches the electrode by means of semi infinite linear diffusion and the potential of the electrode
65. an range vertex potentials output offset ranges of scan rates scan rate resolution accuracy temperature dependence minimum maximum hold mode maximum number of scans monitor output BNC SCAN GEN potential accuracy t1 mV maximum 100 mV s to 10 kV s full scale 6 ranges 5 V relative to initial 2 5 mV resolution and 5 mV SCAN250 5 V relative to initial potential accuracy 0 2 mV maximum 2 5 mV resolution and 2 mV 100 mV s to 10kV s full scale 6 ranges 1 in 4096 1 in 4096 0 2 full scale 500 uV s lt 0 04 K lt 0 04 K 100mV s 100mV s 10kV s 10kV s available available 32767 32767 scan signal scan signal 0 2 full scale 500 u V s ADC750 dual channel fast ADC module number of ADCs maximum conversion rate maximum integration time e basic resolution e resolution of measurements memory ECD low current amplifier module current ranges current measurement type of filter filter time constants compensation of current offset monitor output BNC Appendix V Technical specifications 135 2 each with four input channels 750 kHz 5 5 ms mean of 4096 AD conversions 1 in 4096 12 bit potential 5 mV at range 10 V 2 mV at range 4 V 1 mV at range 2 V current 0 5 0 05 and 0 005 of full scale 128000 samples per channel optionally 512000 samples 100 pA to 100 pA full scale seven ranges 1 pA and 10 pA with sel
66. aph can be edited by double clicking them The following items can be double clicked the axis annotation the axis itself Chapter 3 The GPES windows Fig 30 Horizontal axis window Horizontal Axis Intercept position Min axis range Ticks O Major Scale Linear O Ln O Lg D Square root C Minor Position D17 Square root 17Xx X Square root Y Grids Confirmation O Major LINE ATTRIBUTES CJ Minor the axis description the plot title and subtitle the data Colours sizes marker types text formats axis position all these things can be changed Please take some care with changes in Colours E g do not make the data colour the same as its background colour 61 62 User Manual GPES for Windows Version 4 9 Fig 31 Plot parameter window Plot Parameters Type FAA E O Fill Area ias afiributles Marker Attributes Size le O Drop Line Style Full Empty Empty Dot By double clicking the data points a window appears which among the standard graphical operations also gives the possibility to view the data values itself and to edit them Moreover the data can be copied to clipboard and subsequently be entered into e g a spreadsheet program Fig 32 Graph parameter window Graph Parameters Graph let oe wan Fund coor anta Top o Height 96 3 Border O Plotting rea ft 19 9 width 59 8 C
67. asured data file save the measured data enable auto numbered files names starting with number lt n gt specify the string which should be replaced by a number in the lt filename gt for auto numbered files Start file numbering with number 5 DataSet AutoNum Replace string xxx DataSet AutoReplace xxx Save Automatic number file DataSet SaveAs c autolab data filexxx The first file is now saved as c autolab data file005 ocw Please note When a FRA project is started from GPES and the FRA project and both projects contain the command DataSet AutoNum lt n gt then the number of the FRA project is overruled by the number in the GPES project Dataset PeakSearch Dataset Selectscan lt scanno gt Dataset MinMax Dataset Smooth lt smooth level gt Dataset SaveQ amp Q lt filename gt perform automatic peaksearch with baseline correction select a recorded scan number in cyclic or linear sweep voltammetry for further processing find the minimum and maximum value in a dataset smooth the data using the Savitsky and Golay algorithm The smooth level can be an integer number between 0 and 4 Note that after the execution of the project the smoothed data are replaced by the originally measure data store the anodic and cathodic charge versus scan number Q amp Q files for cyclic voltammetry data The filename must be specified without an extension Dataset Savelmpedance
68. asurement and depends on the speed of the PC that is used and on the type of AD converter included in the Autolab system In general it is possible to get an interval time of approximately 19 us 126 User Manual GPES for Windows Version 4 9 Value of alpha CV staircase Fraction of the time interval between two potential steps at which the current is sampled It should normally be 1 Only in cases where linear sweep voltammetry should be compared with staircase voltammetry this number should be different The number should be at least 0 25 Linear sweep voltammetry equals staircase voltammetry for reversible systems when o 0 25 Ref M Saralthan R A Osteryoung J Electroanal Chem 222 69 1987 Wait after first vertex CV staircase cyclic voltammetry normal or stationary current mode If checked scanning will stop at the first vertex potential and a chronoamperogram will be recorded with duration and sample time as specified The chronoamperogram is not displayed on the screen but the data are stored in memory and can be saved on disk using the File option on the Data presentation window Wait after second vertex CV staircase cyclic voltammetry normal or stationary current mode If checked scanning will stop at the second vertex potential and a chronoamperogram will be recorded with duration and sample time as specified The chronoamperogram is not displayed on the screen but the data are stored in memory
69. ata presentation window A click of the right mouse button is used to open a zoom panel in the Data presentation window or to shrink or enlarge the Graphics panel in the Setup Template option in the Print menu window which appears after selecting Print from the File option in the GPES Manager window Chapter 1 Principles of operation The following keyboard functions are supported RETURN ENTER key jump to next data input field select menu option or click button with focus left and right arrow key move cursor in data input field up and down arrow move up and down in potential current level input in chronomethods or move up and down in a menu ALT puts focus on the menu bar of the window with the focus typing a subsequent underlined character will move the cursor to the corresponding menu item a RETURN ENTER will select the menu item ESC aborts the execution of the measurement procedure Fl access Help F4 plot rescale FS starts the execution of the measurement procedure F6 and shift F6 change focus to the next window This manual does not describe the background of the electrochemical methods We would like to refer to the Electrochemical methods manual and some excellent textbooks C M A Brett and A M O Oliveira Brett Electrochemistry Oxford science publications ISBN 0 19 855388 9 Allen J Bard and Larry R Faulkner Electrochemical Methods Fundamentals and Applications J Wiley amp Sons ISBN 0 471 055
70. aximum value in the data set DataSet MinMax Parameter Information Insert comment Syntax F Use method cyclic and linear sweep voltammetry nie ProcedurelMethod CV Load procedure TESTCY Procedure Open C AUTOLAB TESTDATASTESTC Start execution of the procedure Procedure Start 2 Select scan number 1 Dataset Selectscan 1 Store the data in the file TESTCV in the data directory DataSet Saveds C AUTOLAB DATA TESTCV Use method voltammetric analysis ProcedurelMethod VA Load data file DEMOEAO1 from the testdata directory Dataset Open C ASUTOLAB TESTDATA DEMOEAO1 Perform automatic peaksearch DatasetlPeakSearch OK Cancel pa Se Ss Every project command can be inserted in the project deleted or moved to another place A short description of the command is given in the information and syntax box Using the parameter button one can define the parameters that belong to that specific command Project examples Example 1 Cyclic voltammetry on MUX channel 2 and 4 The following example of a GPES project will perform the c autolab testdata testcv procedure on channels 2 and 4 and stores the results in c autolab data test channel 1 and in c autolab data test channel 4 Procedure Method CV Procedure Open c autolab testdata testcv Utility Channel 2 Procedure Start Dataset SaveAs c autolab data test channel 1 Utility Channel 4 Procedure Start Dataset Sa
71. bz Data present El Edit procedure Ei Paint Shop Pro E Screen Capt oe 12 19 PM The settings in the File menu and the data analysis also depend on the type of technique More details about the available methods can be found in a separate chapter Utilities The Utilities window allows to select electrode control burette control I interrupt positive feedback hardware check cell plate sleep mode set colour defaults and options Chapter 3 The GPES windows 33 Fig 17 The Utilities menu EX GPES Manager Manual control Beles File Method Utilities Options Project Window Help 5 8 Electrode control E Cyclic voltammetry staircase Normal Procedure Democv01 E Burette control RDE control File Copy E MUX control interrupt Positive feedback Calibrate PH Electrode Ferri Ferro Check cell Cyclic voltammetry Plate Sleep mode Set default colors 0 300x10 4 0 200x10 4 0 100x10 VA o4 0 100x10 0 200x107 J 0 300x10 r 7 0 500 0 250 0 0 250 0 500 0 750 E 000V 1 00A Status Messages Disk file Q 1 543E 03C Q 9 369E 04 C Manual control MStar 40 4wa HE Inbox Outloo Ay Exploring R 5 di Microsoft Phat BY Microsoft wor BY GPES Man Bo A GSp 16 44 Electrode control The Electrode control option allows to operate a static mercury drop electr
72. cterised by the dimensionless electrode radius ry Y 1 Dat where reis the radius in meters Dr is the diffusion coefficient of the reactant in m s and Tis the characteristic time parameter of the technique The time parameter T is equal to RT nFV in staircase and cyclic voltammetry V scan rate to pulse time in normal pulse voltammetry and chrono techniques to modulation time in differential pulse techniques and to inverse of frequency in square wave voltammetry If the electrode is large or the t parameter is small fast experiments i e only linear diffusion takes place the dimensionless electrode radius should be set to zero This value indicates that the radius of the electrode is irrelevant All electron transfer rates are normalised according to equation k kit Dx 86 User Manual GPES for Windows Version 4 9 and all homogeneous chemical reaction rates are normalised by multiplication by t K chem k T chem Use of normalised constants allows carrying out fitting without the knowledge of diffusion coefficients In all equations in the description of the models the log function refers to 10 based logarithm and In function to natural e based logarithm Cyclic voltammetry reversible electrode process Reaction equation R gt P Fitable parameters redox potential E V normalised current norm U Tnorm X at A constant background current A Initial guesses available for number of exchanged el
73. d This option is only available for Savitzky and Golay smoothing The popular Savitzky and Golay method is described in Anal Chem 36 1627 1964 Their method presumes that a number of points can be fitted to a polynomial so that the best curve will pass through the experimental points This method is also called weighted moving averaging Before the smooth routine of Savitzky and Golay is applied to the data set spikes in the set of data are removed The Smooth option in all programs first asks which smooth level has to be applied Valid levels are 0 to 4 These levels are 0 spike rejection only 1 spike rejection and a 5 point weighed moving average 2 spike rejection and a 9 point weighed moving average 3 spike rejection and a 15 point weighed moving average 4 spike rejection and a 23 point weighed moving average The applicable smooth level heavily depends on the number of points of the data set The more points within the curve the higher the smooth level can be without modifying the curve too much Having selected the FFT option a logarithmic or linear frequency domain plot is displayed Now a cutoff frequency has to be supplied which should be less than the dominant noise frequency The FFT smoothing algorithm assumes that the signal is composed of n 2 sine waves of different frequencies where n is the number of measured data points filled up to a power of 2 512 1024 etc The added data points get a value of zero A c
74. d the actual interval time can be less For more information see the chapter on the methods Interval time ECD The time between two current measurements in dc amperometry Interval time ECN The time between two recorded current and potential samples It should be gt 0 002 s Interval time VA Time between two measurements Linear 1 or square root 2 distr LSV staircase hydrodynamic The rotation speed table is calculated with a Linear distribution 1 or with a square root distribution 2 A linear distribution means that when the initial speed is e g 100 and the final speed is e g 1000 with 10 scans the subsequent rotation speeds will be 100 200 300 1000 Lowest current range bipotentiostat CV CM The input parameter only appears when the Autolab is equipped with the bi potentiostat module The maximum range is 10 mA the minimum range is 100 nA The actual current range for the bi potentiostat module will be automatically set between the specified highest and lowest current range Maximum dE di or dQ CM interval time gt 1 s In case the box Specify maximum dE di or dQ is checked and if the change in current charge or potential exceeds the specified value a data point will be recorded Appendix II Definition of procedure parameters 117 Maximum time interval CV stationary current After this period the current is supposed to be stationary Maximum time of measurem
75. d to asymmetric tailing voltammetric ones The obtained convolution peak follows the function D K B Oldham Anal Chem 58 1986 2296 J C Myland K B Oldham C G Zoski J Electroanal Chem 193 1985 3 102 User Manual GPES for Windows Version 4 9 e nFAD Ccosh nF 2RT E E eq 5 in case of a fast reversible electron transfer It is also possible to use other convolution functions e g to separate the spherical diffusion effect the kinetic effect of the preceding homogeneous reaction etc In chronoamperometry convolution of current with t function results in a horizontal line at the height equal to e nFAD C eq 6 1f the transport to the electrode follows semi infinite linear diffusion For chronocoulometry convolution with a r function leads exactly to the same result It is profitable to distinguish a class of convolutions with a g f function in the form e 1 1 u is a real number such a convolution can be considered as a generalised differentiation integration differintegration operation with respect to the variable t In this approach the value of the exponent denotes the order of integration if positive or differentiation if negative and thanks to the convolution definition the value of u need not be integer Differintegration is cumulative i e d d1 d i dt di dt or d df di dt d i dt From the practical point of view two forms of convolution with t and
76. d to set markers for the anodic and cathodic branch on the curve In principle this option works similar to Corrosion rate analysis without the fitting part 4 8 Corrosion rate This option allows the determination of the corrosion rate and the polarisation resistance If the current versus the potential curve passes the zero current line more than once the user is asked to define a window of interest around the point where the anodic current balances the cathodic current Before doing this 1t might be useful to draw the horizontal axis through the origin of the vertical axis This can be done by double clicking the horizontal axis and subsequently selecting the Origin in the Intercept position panel If the curve passes the zero current line only once the whole curve is used for the analysis Subsequently the graph is transformed in a logarithmic scaled current versus potential plot and the Corrosion rate window appears This window shows the corrosion potential and the polarisation resistance at the corrosion potential In this window the surface area SA equivalent weight EW and the density D of the electrode material can be specified These data are used to calculate the corrosion rate in terms of current density Ieorrosion and millimetres year CR Icorrosion Icorrosion SA A cm2 and CR 3272 ico EW SA D The polarisation resistance Rp is determined by taking the reciprocal value of the derivative di dE The der
77. der Analysis allows you to determine the half wave potential and the number of electrons for S shaped voltammogram for example a Normal pulse voltammogram The file democv01 may be transferred to an S shaped curve by choosing Edit data Convolution and Time semi integral For more details on the convolution techniques please read the relevant chapter in this manual Chapter 2 Getting started with GPES 15 Fig 6 Results of time semi integral convolution Data presentation File Copy Plot Analysis Editdata Work scan Ferri Ferro Cyclic voltammetry 0 500x10 0 400x10 4 0 300x10 4 0 200x10 4 0 100x10 4 o4 0 100x10 4 0 200x10 0 501 After selecting Wave log analysis you are asked to set markers for the baseline and the limiting current line for the forward or black curve Please set two markers for the baseline and press OK and do the same for the limiting line Now the Wave log analysis window gives you a value for the half wave potential and the height of the curve By clicking Continue the curve transforms and you are again asked to set two markers After doing this and clicking OK you get the results for the analysis in the Wave log analysis window Close this window and choose Plot and Resume 16 User Manual GPES for Windows Version 4 9 Fig 7 Wave log analysis option GPES Manager Manual control
78. dow Close button or Alt C or Close option from the File menu or switch to fitting by pressing Fit button close to the model name or select another model In the last case a new list of parameters appears with their default values Chapter 4 Analysis of measured data 79 Fitting advanced options Fig 51 The Fit control parameters Fit control parameters T Fit contol parameters Maximum change in chi square scaled 01 Maximum fitting time s 0 Maximum number of iterations 50 Number of iterations per fitting step 1 Maximum number of iterations giving no improvement 7 T Simulation control parameters Minimal number of simulation steps per potential value Maximal number of simulation steps per potential value Number of points in concentration gradient calculation Parameter 4 in space transformation y In 1 4 x Use LU decomposition method for boundary condition yNwegas T Fast Fit parameters Data reduction factor 1 10 5 Minimum number of points for Fast Fit 25 820 820 Maximum number of iterations for Fast Fit 15 It is possible to fine tune the fitting process Parameters influencing the fit can be set by choosing Fit control parameters Option menu or by pressing Ctrl P The following parameters appear on the screen Fit control parameters Maximum change of chi square scaled The convergence is reached when the last change in x is not larger than
79. e differing in the degree of reversibility of each electron transfer reversible quasi reversible or irreversible mechanism The parameters are denoted with numbers 1 and 2 to indicate to which component they correspond Reaction equations for single component R 1 P reversible process R ey P quasi reversible process Resp irreversible process Fitable parameters reversible case redox potential E V normalised current norm 1 Inorm X at A quasi reversible case redox potential E V Log normalised electron transfer rate log k transfer coefficient a normalised current Inorm Z Inorm X b0 A irreversible case Log Normalised electron transfer rate at E 0 log ke exchanged electrons transfer coefficient on normalised current norm 1 Inorm X b0 A common parameter constant background current A Initial guesses available for Comments According to the theory the peak current is equal to nFAcpuk MaD X at reversible processes or nFACpu MbD bt irreversible processes where the first term is equal to the fitable parameter norm and the functions y at and x bt represent the shape of the voltammetric peak The parameters a and b are respectively a nFV RT b 0nFV RT V being the scan rate The peak values of these function are 0 4463 reversible and 0 4958 irreversible for linear sweep voltammetry If voltammetry with staircase voltage ramp is used the exact value Chap
80. e and the current sampling parameter 0 Details regarding the function x br can be found in literature There is no need to set the number of exchanged electrons because the term an is fitted as a whole Cyclic voltammetry reversible electrode process followed by irreversible chemical reaction ECi Reaction equation Re P Le B Fitable parameters redox potential E V forward chemical reaction rate kc foll gt norm kef normalised current Inorm I Inorm X bt A constant background current A Initial guesses available for number of exchanged electrons E gt Inorm background current 88 User Manual GPES for Windows Version 4 9 Comments The forward chemical reaction rate is normalised with respect to the time scale of the voltammetric experiment k y k RT nF v Similarly to previous cases the voltammetric peak current is expressed as a product of the peak shape function X bt and the term including the electrode area concentration diffusion coefficient and the number of exchanged electrons Details regarding this mechanism can be found in literature Cyclic voltammetry two component models Two component models represent the situation when two electroactive species are reduced or oxidised at the electrode independently from each other In such situations their peaks can overlap what hinders the extraction of relevant parameters for separate reactions There is a number of two component models availabl
81. e contribution of spherical diffusion appears Apart from the geometry of electrodes chemical processes taking place in the solution can disturb the concentration profiles developed during the electrolysis for instance when electroactive species are produced by a homogeneous chemical process another example of deviations from the linear model may be caused by the adsorption of the compound on the electrode surface It can be useful to consider different types of transport as deviations from the semi infinite linear diffusion case These deviations can then be classified into two groups deviations causing an increase of the transport to the electrode and those causing a decrease In the first group spherical diffusion and different kinetic effects are included the second group covers effects such as limited diffusion and reaction from the adsorbed state Spherical diffusion enhances the transport because the spherical expansion of the diffusion zone increases its volume faster than in the semi infinite linear case The increased volume results in a larger amount of the substance that diffuses to the electrode Kinetic effects occur when the electroactive compound is involved in a chemical equilibrium The local decrease of its concentration within the diffusion layer disturbs the equilibrium and in consequence leads to the production of the compound in a chemical process This extra amount increases the flux of the substance to the electrode surf
82. e for manual control over the potentiostat galvanostat one for data presentation and manipulation one for entering the experiment parameters and one for collecting results of data analysis Surrounding windows menu options and tool bars give extra facilities like cell diagnosis accessory control Autolab configuration access and data transfer to programs like Excel and MS Word The MS Windows related terminology used in this manual is in agreement with the standard as described in the book The GUI Guide international terminology for Windows Interface Microsoft Press Washington ISBN 1 55615 538 7 Itis a good book to become acquainted with the Windows vocabulary The following mouse conventions are used Quickly pressing and releasing the mouse button is called clicking A click of the left mouse button on a menu option a button an input item on the screen etceteras will result in an action Clicking and holding down the left mouse button is called dragging and is used for several purposes You can focus on an item on the screen without an action you can drag a window when the mouse pointer is in its title bar It can be used to shrink or to enlarge a window when the mouse pointer is on the border of a window Finally you can drag a scroll bar a slider or a zoom panel A double click of the left mouse button is used to perform particular actions Except for the standard uses in window actions 1t is used to edit the graph in the D
83. e kinetics and reversibility of the electrode process The dt dE vs E plot can be used for electroanalytical purposes Show forward This option shows for the techniques square wave and differential pulse voltammetry only With square wave voltammetry it allows to toggle the display of the current measured in the pulse which is applied in the scan direction With differential pulse voltammetry it allows to toggle the display of the current before applying the pulse Show backward This option shows for the techniques square wave and differential pulse voltammetry only With square wave voltammetry it allows to toggle the display of the current measured in the pulse which is applied in the opposite of the scan direction With differential pulse voltammetry it allows to toggle the display of the current measured in the pulse 60 User Manual GPES for Windows Version 4 9 Load overlay file This option allows the making of a graphical overlay of one or more data sets A maximum of 10 overlays can be made You can select multiple files at a time by using lt Shift gt or lt Control gt combined with the mouse action The overlay legends shown in the Data presentation window will also be visible in a print out After clicking the New plot option or the Resume option the overlays will disappear It is possible to load overlays together with the main data see Load data scan option of the File menu Reverse axes This option will reverse
84. e simple algorithm ym y n 1 ym 1 yin dy dx n 0 5 _ 0 5 x n x n 1 x nt 1 x n For cyclic and linear voltammetry the time derivative is given i e x is the time since the start of the scan instead of the potential 5 8 Integrate The integral is determined using the trapezium rule which assumes a straight line between two data points For cyclic and linear voltammetry the time integral is given i e x is the time since the start of the scan instead of the potential 100 User Manual GPES for Windows Version 4 9 5 9 Fourier transform The frequency spectrum is determined by means of a Fast Fourier method FFT The real frequency is displayed on the x axis 5 10 Convolution techniques Convolution voltammetry consists essentially of a voltammetric chronoamperometric or chronocoulometric experiment followed by a mathematical transformation convolution The technique delivers quantities directly related to the concentration of electroactive species at the electrode surface instead of the flux of a compound as in the case of the original techniques and it is rather insensitive to iR drop Fig 53 Convolution menu GPES Manager Manual control of x File Method Utilities Options Project Window Help AE Ja gt ul aj 48 2 Cyclic voltammetry staircase Normal Procedure DEMOCV01 0 130 0 400e 3 File Copy Plot Analysis MERIGREY Work
85. e space grid exponentially expands with the distance from the electrode surface This is obtained by transforming the space in such a way that the increasing distances in the real space correspond to equally spaced distances in the transformed space The program uses Feldberg s function y In 1 Ax for space transformation and the rate of expansion thus also the number of points in concentration profile is controlled by parameter A This parameter should be in the range 2 3 and its default setting is 2 Chapter 4 Analysis of measured data 81 Use LU decomposition for boundary condition This is the option to provide an alternative way to solve the matrix representing boundary condition at the electrode surface The matrix is highly sparse and it is usually solved by direct method However it can happen that the LU Lower Upper decomposition method gives better results in some cases but it is significantly slower when the number of points used to calculate concentration gradient increases Default setting is not to use LU method Fast Fit parameters See Fitting in more detail Full and Fast fit Data reduction factor Allows to carry out fast fit with a data set reduced by this factor in the reduced data set points are evenly spaced The actual value of this factor depends also on the minimal number of points for fast fit For more information consult Fitting Fast and Full fit Minimum number of points for Fast Fit This is
86. eaction with the rate k can be eliminated by means of inserting different values of k one can obtain the result in which a convoluted current at the end of the cycle approaches the same value as on the beginning of the cycle Some problems can be expected if the substrate or the product of the reaction is accumulated on or in the electrode by adsorption deposition or amalgamation In this case the initial value of the surface concentration is not restored after the completion of the voltammetric cycle and convoluted voltammograms will not deliver proper results Investigations of factors controlling the transport to the electrode Theoretically the most simple and quite commonly encountered transport type is semi infinite linear diffusion the substance diffuses from the bulk of the solution where the concentration is constant to the planar electrode where it is consumed The flux of the substance depends on the gradient of the concentration at the electrode surface this gradient decreases with the rate proportional to the square root of the electrolysis time Linear diffusion leads to the simplest description but unfortunately its conditions are rarely realised in the experimental setups used in electrochemistry In case of mercury electrodes the surface of the electrode is not planar and the diffusion can be approximated using a linear model over a short period of time only In case of solid electrodes a so called edge effect occurs th
87. eckbox After selecting the Check Cell option the Check Cell window appears After pressing the measure button the program will start checking the electrode connections and will then measure the noise level With the unshielded cable over the monitor you will see the current levels in red and the software will give you a warning that the noise level is too high Please redo the measurement without the unshielded cable You will now see the current levels in black indicating that the noise level is acceptable Please use this option if you have doubts about the noise level in your system Chapter 3 The GPES windows 27 3 The GPES windows 3 1 GPES Manager window The title bar of the GPES Manager window contains several options i e File Method Utilities Project Window Help File menu This menu contains options which are usually present in Windows programs Fig 15 The File menu GPES Manager Manual control of ES Method Utilities Options Project Window Help Open procedure Ctri O S Le Cyclic voltammetry staircase Normal Procedure DEMOCY01 Save procedure Ctrl S Save procedure As Tax anual conira x Print Ctrl P Current range Settings Potential iR compensation dle q forma eJa o ala 4 Load scan F100mA Load data buffer Pe 10mA High Sens off 000 0 Ohm Save scan As N
88. ect to the open circuit potential OCP Before the equilibration starts the OCP is recorded If sufficiently stationary a button can be pressed to continue Define start potential w r t OCP CV If this item is checked the measurement starts with measuring the OCP After acceptance the Start potential will be corrected for the OCP Start potential OCP If you want to start at the OCP Define vertex potential w r t OCP CV If checked the vertex and start potentials are specified with respect to the open circuit potential OCP Before the equilibration starts the OCP is recorded If sufficiently stationary a button can be pressed to continue Deposition potential VA This is the second potential applied after the start of the procedure This potential is normally applied to deposit the components to be analysed on the electrode This potential is not applied when its duration is set to zero Direct output filename CM interval time gt 1 s If a file name without extension is specified the measured data are directly written to a data file with the extension oxw This option may be useful for long duration measurements It prevents loss of data due to a failure in the power supply Appendix II Definition of procedure parameters 115 If the number of measured data points exceeds the allowed maximum default 10 000 the program will continue to store the data points on disk although the data points are no longe
89. ectable gain amplifier 0 5 accuracy third order Sallen Key RC times 0 s 10 ms 100 ms and 500 ms 10 uA maximum current BIPOT ARRAY and BA bipotentiostat module current ranges current measurement maximum current output potential range potential accuracy monitor output BNC FI20 filter and integrator module e filter section type of filter filter time constants output offset monitor output BNC integrator section ranges charge measurement temperature dependence monitor output BNC BIPOT ARRAY BA 100 nA to 10 mA full scale 10 nA to 10 mA full scale 6 ranges 7 ranges 0 2 of current 0 2 0 2 of current 0 2 of current range of current range 35 mA 50 mA 5V 10V 0 2 2 mV 0 2 2 mV current current third order Sallen Key RC times 0 s 10 ms 100 ms and 500 ms 2mV filter output 10 ms 100 ms 1 sand 10 s 0 2 accuracy lt 0 04 K charge output BSTR10A or Booster20A current booster maximum output voltage maximum output current maximum output power bandwidth current measurement dimensions W x D x H weight BSTRIOA 20V 10A 200 W 4 kHz full power 10 A full scale 0 5 accuracy 37 x 36 x 15 5 cm approx 9 kg Note Specifications subject to change without notice All specifications at 25 C Booster20A 20 V 20A 400 W 20 kHz 1 of full scale 20mA 52x 42x 17cm approx 25 kg Index 137 Ind
90. ectrons E gt Inorm background current Comments According to the theory the peak current is equal to nFAcpuk MaD Pg at where the first term is equal to the fitable parameter fnorm and the function x at a nFV RT V being scan rate represents the shape of the voltammetric peak The peak value of this function is 0 4463 for linear sweep voltammetry while for voltammetry utilising the staircase voltage ramp the exact value depends on the step height step time and the current sampling parameter Q Details regarding the function at can be found in literature Cyclic voltammetry quasi reversible electrode process Reaction equation R A sp Fitable parameters redox potential E V Log normalised electron transfer rate log k transfer coefficient Ql normalised current Inorm I Inorm b0 A constant background current A Initial guesses available for number of exchanged electrons log k E rias background current Comments The parameter log k is a 10 base logarithm of the electron transfer rate Ss normalised with respect to the time scale of the experiment k k RT nFVD where V is the scan rate and k is the electron transfer rate used in Butler Volmer equation R S Nicholson and I Shain Anal Chem vol 36 1964 page 706 Chapter 4 Analysis of measured data 87 I k e expl onF RT E E c exp 1 onF RT E E According to the theory the peak current is equal to nFAcpux
91. ed the scan direction will be reversed if the current exceeds the specified value Reverse scan for i lt CV If Specify current boundaries is checked the scan direction will be reversed if the current becomes lower than the specified value Run time ECD The duration of the measurement Save every nth Cycle CV When more then one scan is to be recorded in Cyclic voltammetry it is possible to save scan at regular intervals during the measurements If this parameter is zero no scans will be saved during the measurements otherwise every nth scan will be stored on disk If e g 5 is specified scan 1 5 10 15 are saved The path and the name of the file can be specified on page two of the Edit procedure window Direct output filename The last five characters of the file name will be used as the scan number Please note These files can be overwritten during another measurement session with the same procedure Scan rate CV Staircase The required speed of potential change The lowest scan rate is 0 00001 The highest acceptable depends on the speed of the AD converter the computer and the step potential The essential number for the highest scan rate is the number of potential steps per second i e scan rate step potential The maximum value is 4 800 with normal CV 2400 with Bipot or grg Signal With Fast scan CV the maximum value is 45 000 The specified value is adjusted by the program so that the numb
92. eed to be specified Duration of the interrupt The interruption period a reasonable value is 001 to 01 The shorter the better First second marker The data point numbers between which a straight line is fitted In total 20 points are measured After the parameters have been specified the Measure button can be clicked The measured data are subsequently plotted and the straight line is drawn The calculated uncompensated resistance is printed in the Result panel Now the Set marker button is available When clicked you can change the First and Second marker value by clicking two data points on the measured curve 38 User Manual GPES for Windows Version 4 9 Fig 22 Example of the results of a current interrupt measurement Data presentation File Copy Plot Analysis Editdata kinterrupt dummy c Linterrupt Range vc 1Ve Duration of interrupt 0001 15 003 First marker 1 123 4 Set markers Second marker 1 123 13 Result Ru calculated 104 5 Ohm Measure Close 0 0005 0 0010 0 0015 0 0020 0 0025 0 0030 0 0035 tis The calculated uncompensated resistance can be used as an estimated start value to be used in the Positive feedback option See next section WARNING Too high Ohmic drop compensation can cause oscillation of the potentiostat which may cause damage to the working electrode An example of the use of J interrupt is given in the chap
93. eesetsecsseeseeseeseeeeceeeeseesesseeeceseseseeeaseaeeateae Table of contents 3 Chapter 1 Principles of operation 5 1 Principles of operation 1 1 Preface Autolab and the General Purpose Electrochemical System software GPES provide a fully computer controlled electrochemical measurement system It can be used for different purposes i e general electrochemical research polarographic analysis in conjunction with a dropping or static mercury drop electrode voltammetric analysis with solid electrodes such as glassy carbon or rotating disk electrodes research of electrochemical processes like plating deposition and etching electrochemical corrosion measurements electrochemical detection in Flow Injection Analysis FIA and High Performance Liquid Chromatography HPLC The instrument is controlled by a personal computer equipped with an IBM PC or AT I O expansion bus All the Autolab configurations are supported by GPES uAutolab or JH Autolab Type II the compact version of a standard Autolab with potentiostat Autolab with potentiostat galvanostat PGSTAT10 12 20 30 100 and other optional modules The GPES combines the measurement of data and its subsequent analysis GPES runs under MS Windows 95 98 and NT Its installation is described in the Installation and Diagnostics guide The user should be familiar with MS Windows The GPES program consists of two distinct parts 1 e The user interface graphics and data analy
94. electrode process analytical quasi reversible electrode process analytical and irreversible electrode process analytical These models differ from the previous only by the fact that each point of the normal pulse voltammogram is calculated from analytical expressions for chronoamperometry under the following assumptions the current is measured at the end of the potential pulse before each potential pulse concentrations of the species at the electrode surface are the same as in the bulk of the solution The latter means that no significant electrode reaction occurs at the base potential and that the interval time is long enough to restore the initial concentrations or the dropping mercury electrode is used In addition to this it is assumed in the reversible model that the product of the electrode reaction is initially absent in the solution Thanks to analytical expressions the speed of calculations is much higher than in the regular model based on finite difference simulation Therefore if the mentioned assumptions are valid this model should be preferred Differential pulse voltammetry reversible electrode process Reaction equation RES P Fitable parameters peak potential E V peak current Jp A constant background current A Initial guesses available for number of exchanged electrons Ep Ip background current Comments The approximate expression for the peak height valid under linear diffusion conditions is Ip
95. els specified with a current equals 0 A This feature assures zero current If this option is not checked the current is set to zero with the cell switch on This means that a small offset current of maximum 0 2 of the selected current range can flow Tafel plot CV If checked the x axis becomes the 10Log axis of the measured current and the y axis becomes the potential axis This option has been added to allow presentation of traditional Tafel plots It does not give any functional contribution Unless required it is recommended to use this option Normally recorded voltammograms can always be converted to corrosion plots Load previously measured data check corrosion plot save the data again reload the data Now the data should be presented as a corrosion plot Third conditioning potential CV CM ECD The third potential which is applied after the Start button has been clicked If the corresponding Duration is zero the potential is not applied Time to wait for OCP CV CM The time you want to wait for acceptance of the Open Circuit Potential If this time has expired the program will continue using the OCP measured at that time If this parameter is O zero the program will not continue unless the Accept button is pressed If O zero is specified in a procedure that is used in a project the program will wait for 2 seconds at the OCP and will use the OCP measured at that moment Title and subtitle All Text l
96. ents PSA The measurements will stop when duration of the measurement exceeds the specified time Measurement temperature CV CM with pH as second signal Temperature for pH correction with respect to the calibration temperature Minimum abs di i per second CV stationary current Every second the relative current change is determined If during three seconds this relative change is less than the specified value the current is supposed to be stationary The next potential is applied Minimum abs di per second CV stationary current Every second the absolute current change is determined If during three seconds this relative change is less than the specified value the current is supposed to be stationary Minimum variation CM Value at which the experiment is stopped or the next step in the experiment will be applied This value is only active if the Specify minimum variation is checked Modulation amplitude VA differential pulse The height of the potential pulse The pulse direction is the same as the scan direction when the specified amplitude is positive If a negative amplitude is specified the pulse direction is reversed with respect to the scan direction Modulation amplitude VA differential normal pulse Potential superimposed on the sum of base potential and pulse amplitude Modulation time VA Time during which the modulation amplitude differential pulse differential normal pulse or the sine wa
97. epending on u using GO or FRLT algorithm spherical convolution and kinetic convolution The difference between GO and FRLT algorithm is that GO is more exact while FRLT is faster with large data sets Two items semi integration and semi differentiation denote differintegrations using FRLT with the u value equal to 0 5 and 0 5 respectively It is possible to carry out more transformations in succession Because differintegration is an operation that can be cumulated double semi differentiation is equivalent to differentiation and the integration followed by semi differentiation is equal to semi integration Please note that some combinations especially those involving differentiation are not equivalent differentiation integration is not the same as integration differentiation In all convolutions the scale on the Y axis represents c OnFAD where c f is the concentration of the product of the electron transfer step on the surface of the electrode 110 User Manual GPES for Windows Version 4 9 Fig 57 Example of a convoluted voltammogram 0 696 0 049e 5 File Copy Plot Analysis Editdata Work scan Simulated data 0 300x10 Check peaksearch convolution and FiteSimulation 0 250x10 0 200x10 4 0 150x10 4 0 100x10 4 0 050x10 4 0 0 050x10 4 T T T T T T T T 0 400 0 450 0 500 0 550 0 600 0 650 0 700 0 750 0 800 E V It is also possible to perform the convolut
98. er of steps per second becomes equal to one of the discrete values of the Autolab hardware timer The maximum values might vary in combination with advanced options like Specify current boundaries High sensitivity alpha different from 1 and Chronoamperometry at vertexes Scan rate CV Linear scan The required speed of potential change The lowest scan rate is 0 001 This is a hardware limitation of the SCAN GEN module The highest scan rate is 10 000 V s for the SCAN GEN module As stated above no more than about 4 800 samples per second can be taken in combination with the ADC164 or ADC124 module This limits the measurable scan rate to about 10 V s Higher scan rates can be measured with ADC750 module which allows to measure 750 000 samples per second Second conditioning potential CV CM ECD In galvanostatic cyclic voltammetry or galvanostatic chronopotentiometry potential should be read as current and vice versa Appendix II Definition of procedure parameters 121 The second potential which is applied after the Start button has been pressed If the corresponding Duration is zero the potential is not applied Second potential boundary CV Used in combination with First potential boundary for automatic calculation of the total positive and total negative charge Only active when Use boundaries for Q Q calc is checked Second vertex potential CV cyclic
99. erimental factors on the convolution curve can be found in Goto M Oldham KB Anal Chem 46 1974 1522 Linear and staircase voltammetry The convolution techniques facilitate the interpretation of voltammograms particularly the information included in the peak shape As already said this shape can be considered as produced by the convolution of two functions function I describing the surface concentration of the reaction product and function II representing the flux of the reaction substrate depending on the geometry of the measuring system In the simplest case of semi infinite linear diffusion and fast electron transfer function I has the form of an S shaped wave and function II is a t decay The character of function I is well reflected in the ascending branch of the voltammetric peak function Il is responsible for the ps proportional decay of the descending branch of the peak Semi integration convolution of the SCV peak with a t function should therefore give a wave with a horizontal plateau When the transport to the electrode is enhanced or diminished compared to semi infinite linear diffusion the descending branch of the SCV peak can be approximated using a t function where u gt 0 5 for faster transport slower decay and u lt 0 5 for slower transport faster decay Changes in transport result in semi integrated waves with a biased plateau negative for slower transport positive for a faster one Algorithms for con
100. erivative The 2 derivative and endpoint are calculated using the last applied level If only one level is defined all calculations are done on this particular level The 2 derivative values are normalised so do not pay attention to the absolute values The 2 derivative plot is used for indicative purposes only The show 2 derivative button is active after the Find endpoint button has been pressed The Show last level button appears only if more then one level is measured If the amount of measured point is poor the indicated end point in the curve can be slightly different from the actual zero crossing in the 2 derivative The pointer can only be set on a real data point and not on an interpolated point in between 96 User Manual GPES for Windows Version 4 9 Fig 52a Coulometric titration plot GPES Manager Manual control File d Utilities Options Project Window Help Cueca al Data presentation File Copy Plot Analysis Edit data 11 000 10 000 9 0004 8 0004 pH 7 0004 6 0004 5 0004 4 0004 3 000 0 2 500 Endpoint Coulometric titration Bele Results Fra cee ind endpoint Chrono methods interval tine gt 1 s Potention Endpoint s found L__Endenchort 1 pH 7 152 Q 1 0700E 01 C Show 2nd derivative Close a Filter for derivative 1 25 10 Coulometrische Titration Window fO Zao OENE 100 1 5 000 7 500 10 000 12
101. es are set or when very high accuracy is desired automatic settings may be insufficient The simulation options are set by choosing Fit control parameters from the Option menu The middle part of the appearing window contains parameters that control the way the calculations are carried out These parameters are presented below Minimal number of simulation steps per potential value The minimal number of simulations cycles carried out for each value of the potential If this value is set to N then each potential step time is divided into N subintervals and the simulation is carried out for each of these subintervals with time step equal to 1 N fraction of the step time The default value is 4 Maximal number of simulation steps per potential value The upper limit for the previous parameter Number of points in concentration gradient calculation The value of the current is calculated from the derivative of the reactant concentration at the electrode surface In digital simulation the values of concentrations are discrete and defined only in grid points and in calculations of concentration gradient the specified number of points is used Use of many points usually gives a better precision of the calculated current On the other hand the increase of number of the datapoints significantly increases the execution time The default value for this parameter is 2 Parameter A in space transformation y In 1 Ax To speed up the calculations th
102. ex A AC VOItAMIMEHIY nesses ionii seserinis rinier 113 116 117 118 Analysis results es nee eea e e EAEE E E EAE EEEE O EEE RGE 64 AOO a a e de oc a a rE a Ean 59 AS AMA MM E A E E E EE ENE 58 60 B BAS DigiStims sinos oireet eao Eea aka aE eaa ee aat aao 30 DASE CURVE AEA E EET E E E ee AE 67 Pase hne td N id 44 67 68 74 98 110 A Ee A ER a E AS 43 Burette lt COnthOl on ke Mae A EAA a e A aa e Soe E ale 34 C Calibrate pH Electrode sisii etrn ipiri e e EEEE aa E EEEE 39 CHECK CEM TEE N EE E O E E E TA ETE 40 42 Chronoamperometric plot issiria eens iaiiaeeeai a iania 69 ChronoamMperOmMe try cuida Nada 100 102 107 Chronocoulometric ploten iieii i asiani iiin 69 ANN A TT 56 100 102 107 EOL MAA e en dee a 7 47 63 A RN A ES 61 63 COMPUTE ne io 5 6 115 117 120 NA A IO 5 6 42 COMVOIUUIONY Saco overstate Pe dos od ete ten a ed A etc Saks Ricki Se ad og stadt Saeed 108 Convolution 532 55 sehen Ea eae es 70 100 COPY sed i A RN tie R 43 58 64 COLLOSION 3220 ees aie saa eee eee ee EL 5 71 72 73 124 COLTOSTOMIALE vers A da oye kane ees 19 71 72 73 Coulometric titration ees 5 ses edi A o 95 Crank NIC O SOM it ii bn 75 A 95 A O 37 54 55 113 CULV CUL a ide 67 cyclic OMAN oi A REE RE EE on cn AER 104 126 D Pata DUMET E ab ost ddl 31 Delete TICS excise a teases edo dena ee roca San ae cade as te te 31 SUVs aE 68 69 71 99 101 103 104 121 differential Pulseira ennon ieee iene eE EEEE EEEa AAE EEEE OE Oa REE
103. ferential pulse Square wave Sampled DC Normal pulse Appendix IV Multichannel control 131 Cyclic voltammetry Normal Linear sweep voltammetry Normal Chronomethods Amperometry Potentiometry During the measurements the sampling duration is the same as in the normal GPES This is described in the chapter about the Methods However in the multichannel mode all six possible channels sampled one after an other So the number of samples per channel from which the average registered current c q potential value is one sixth of the normal GPES If a channel is specified as active it only means that the measured current c q potential is registered The minimum sampling time is equal to 6 ranged AD conversion and this is 6 times as long as in normal GPES This has a consequence for the minimum interval time in Chronomethods with short interval times The minimum time is now about 800 microseconds see also the information about the manual control window Specifications of the instrument are almost similar to those of the PGSTAT10 potentiostat Appendix V Appendix V Technical specifications maximum output current maximum output voltage potentiostat galvanostat potential range applied potential accuracy applied potential resolution measured potential resolution current ranges applied and measured current accuracy applied current resolution measured current resolution at current range of 10nA potentiosta
104. for 0 001 s and the decay of the potential in time is measured Please click the Measure button After a short time in the result panel a value of about 100 should appear When you want to compensate for 90 of this value never use 100 of the measured value you can do this by typing the value in the iR compensation panel in the Manual Control window After clicking the iR compensation button the program will automatically compensate the measurements for the value given 24 User Manual GPES for Windows Version 4 9 Positive feedback With positive feedback you can give in values for the resistance yourself and you can see when the current starts to oscillate i e when you have overcompensated the resistance a Please choose the Positive feedback option in the Utilities menu an iR compensation will appear in which you can type the following values Potential pulse 0 1 V Duration 0 01 s Connect dummy cell C and put the current range to 1 mA After pressing start the program will start applying potential pulses By giving different values in the iR compensation panel and watching the change in the i t curve you can check how high the uncompensated resistance is Please check the change after typing a value of 95 Now do the same after typing 130 you will see oscillations appearing you have now done overcompensation Please note that if you reach a value where the current starts to oscillate you should use 90 of
105. fter the pre treatment begins Step potential CV The potential increment between two successive current measurements The specified value is adjusted by the program so that it becomes equal to the closest 16 bit DAC164 or 12 bit DAC124 value and the number of steps per second becomes equal to the closest value of the Autolab hardware timer See also Scan rate In galvanostatic cyclic voltammetry or galvanostatic chronopotentiometry potential should be read as current and vice versa In galvanostatic cyclic voltammetry or galvanostatic chronopotentiometry potential should be read as current and vice versa Appendix II Definition of procedure parameters 123 Steps and sweeps table SAS A table in which up to 10 potential level or sweeps can be defined The following items can be specified Segment type Not used This level will not be included in the measurement Step One potential can be applied during a given time The current is sampled with the specified interval time Staircase sweep The potential sweeps from the previous applied potential to the End potential with the specified scan rate The current is sampled at the end of every potential step If the segment type of the first level is specified as a sweep the start potential equals the Standby potential Linear sweep Equal to Staircase sweep but performed with SCAN GEN module If the SCANGEN module is present it is only possible to select
106. h upper and lower case characters can be used in command lines Space characters are ignored If during the execution an error occurs the project continues with the next line An error message will be printed in the Results window One line per command The following commands are allowed lt string gt rem lt string gt comment Procedure Method lt method id gt define the electrochemical method Procedure Open lt filename gt open a procedure file Procedure SaveAs lt filename gt save the procedure file Procedure Start start the execution of the procedure Procedure AddToStandby lt real gt Adda value to the standby potential Only available for Chrono Ampero and Chrono Coulometry experiments Procedure AddToPotlevel lt real gt Add a value to all specified potential levels Only available for Chrono Ampero and Chrono Coulometry experiments Procedure AddToPotlevelEx lt n gt lt real gt Adda value to a specific potential level n Only available for Chrono Ampero and Chrono Coulometry experiments 44 User Manual GPES for Windows Version 4 9 Procedure AddToCurlevelEx lt n gt lt real gt Dataset Open lt filename gt gt Dataset SaveAs lt filename gt Dataset AutoNum lt n gt Dataset AutoReplace lt string gt Example see below Add a value to a specific current level n Only available for Chrono Potentiometry experiments open a previously me
107. he number of iterations and the goodness of fit parameter chi square are given Chi square is the sum of the squares of the differences between measured and calculated data The fitted slopes are s1 and s2 The fitting procedure can be interrupted by clicking the Stop button The comparison between the observed and the calculated curve is shown The Tafel slope parameter amp can be obtained from the slopes b 2 303 RT 3anF F Faraday constant 96484 6 C mol R Gas constant 8 31441 J mol K T temperature 298 15 at 25 C n no of transferred electrons 2 303 ln 10 It is sometimes possible to improve the fit by clicking the Restart button 4 9 Spectral noise analysis After recording current and potential noise transients it is commonly desired to perform a statistical or frequency analysis on the results The GPES software enables the calculation of a frequency spectrum for current and potential or impedance It can be activated in the Analysis menu of the Data presentation window The frequency spectrum is calculated by means of a FFT algorithm Since it requires the dataset to be a power of 2 the number of datapoints is automatically extended when necessary In case of an interrupted measurement lt Abort gt was pressed the dataset is padded with zeros In principle the Fourier method should only be used on datasets that are periodical and fit exactly in the time duration of the recorded scan For noise signa
108. he option button selected The option button 2nd Sig appears in case a chronomethod or the method cyclic or linear sweep voltammetry is selected and the Record second signal option is checked on page 2 of the procedure parameter list The Clock off on button in the lowest of the two panels starts the timer and displays the measured data from the panel above in the Data presentation window This makes it possible to display graphically what is going on These measured data can be replotted printed and the graph can be stored However the data can neither be saved analysed nor edited Noise meters The noise levels for current and potential signals are visualised by 2 noise meters at the signal panels When these VU meters are active the first green LED or a grey background is shown The VU meter for the current signal is only active when the cell is switched on The VU meter for the potential signal is also active when the cell is switched off i e no current can flow During the execution of the procedure except for pre treatment stage the VU meters are inactive In case more than 4 LED s of the VU meter are on it is advised to take precautions You can select a higher current range or minimise the noise of your electrochemical cell High potential noise levels are often caused by the reference electrode iR compensation The R compensation panel appears only when the Autolab is equipped with a PGSTAT12 20 30 100 potentiostat gal
109. hree channels 1 48 26 x 26 x 10 cm3 3 6 kg 4 2kg FRA2 144 W 100 240 V 50 60 Hz GPES for Windows Version 4 9 Autolab with PGSTAT12 no optionally available 10 and 100 ms land 10s USB 16 bit with software programmable gains of 1 10 and 100 2 16 bit four channels optionally eight 1 48 52 x 42 x 17 cm3 18 kg 247 W 100 240 V 50 60 Hz Autolab with PGSTAT302N yes optionally available 10 and 100 ms land 10s USB 16 bit with software programmable gains of 1 10 and 100 2 16 bit four channels optionally eight 1 48 51 5 x 41 6 x 16 cm 18 kg 247 W 100 240 V 50 60 Hz Autolab with PGSTAT100 on request BSTRIOA only optionally available 10 and 100 ms land 10s USB 16 bit with software programmable gains of 1 10 and 100 2 16 bit four channels optionally eight 1 48 52 x 42 x 17 cm 21kg 300 W 100 240 V 50 60 Hz Notes 1 Measured at 1 mA current range 1 kOhm impedance high speed mode when applicable All specifications at 25 C Interface for mercury electrodes IME 303 and IME663 Supported electrodes Metrohm VA Stand 663 e EG amp G PAR303 A e dropping mercury electrodes with knock off hammer Control lines new drop purge on off e stirrer on off Burettes Metrohm Dosimat 665 765 Schott T90 and T100 Hardware specifications of optional modules SCAN GEN SCAN250 analog scan generator module sc
110. ibration for the measurement Check cell The Check cell option allows to check the electrode connections and the noise level When selecting this option an empty window appears with a Cancel and a Measure button First apply a proper electrode potential and current range on the Manual control menu Subsequently click the Measure button The window will subsequently give information about the Electrode connections by comparing the applied and measured electrode potential Also during 0 100 second the current is sampled at the highest rate possible Fig 23 The Check cell window Cancel Check Electrodes All OK 909 000 mA 909 000 mA 909 000 mA 909 2 000 mA 909 2 000 mA Chapter 3 The GPES windows 41 The next figure shows a noisy signal displayed after pressing Measure The plot clearly shows periodic noise with a frequency of 50 Hz After optimising the cell simply by removing the unshielded cable of the reference electrode the same measurement shows a better signal to noise ratio Fig 24a A noisy signal Data presentation File Copy Plot Analysis Editdata Check cell 0 310x10 0 308x10 4 0 305x10 4 0 30310 J 0 300x10 0 298x10 4 0 295x10 4 0 293x10 0 290x10 a Fig 24b A better signal to noise ratio File Copy Plot Analysis Editdata Check cell 1 0 3003x10 0 30
111. icsnnana nano aeo aK EAER nesas 117 121 126 AMAS DA e EE E EN 53 SUIPACE Mande merienenn Eai Si EEEE session E E TAE ER i 95 T Tafel slopen Arnee e r e EAE a E REEE E E EE T REE 70 71 72 73 A A 6 52 ansiosa dt a dia 59 74 TIS SED TNA 49 51 V VIE WINS datane ii oi tas e EEA E ceded saved EA EE A E Ra 60 voltammetric ANAlySis eis iseit aeaa E ER E a S E e ia aTi 5 63 70 W E A RN 16 70 WE 2 Versus WE plot emiren irnia once sssosue ce casas steveateoss connnba sev ouacagesdecccaasbdadseansazeees 95 Window for Zero CLOSSINGS s 5c6 s 2sssetctadsesessszedshbndacdeeetdecacanstucheeedencoavaned shen cea onsets 96 NANA AAA EN 74 Work pot A A cls A A ET e ie 60 Work scanneren maa a dale dede lotes oa RE 60 65 Z
112. imal number of points in the reduced data set and the maximal number of Fast Fit iterations can be set Using Fast Fit can be particularly useful when initial guesses do not deliver good estimates of the parameters or when fitting process tends to oscillate 82 User Manual GPES for Windows Version 4 9 Choosing parameters to fit Each model is defined by a number of parameters These parameters are measurement parameters e g start potential scan rate general parameters e g temperature and specific parameters e g diffusion coefficient standard redox potential etc From these parameters only some can be fitted and they are called fitable parameters The general rule is that only specific parameters can be fitted From them parameters that can acquire only certain values for example the number of electrons involved in the process are not fitable It is only possible to fit successfully parameters that are independent on each other 1 e change in the model due to variation of a certain parameter cannot be obtained by combination of variations of other parameters Although models are built in such a way that interdependent parameters are avoided it can happen that the particular data set renders two parameters dependent or partially dependent An example of such situation is a data set obtained in cyclic voltammetry with a quasi reversible system if scan potentials are chosen so that only one peak cathodic or anodic is visible i
113. inear sweep voltammetry chronomethods voltammetric analysis multi mode electrochemical detection potentiometric stripping analysis steps and sweeps electrochemical noise ocw OXW oew odw opw ofw onw These data files are in ASCII format and are stored in the data directory Data memory buffer in binary format for cyclic and linear sweep voltammetry bew cvl cv2 cv3 These data files are in binary format and are stored in the data directory Data memory buffer in ASCII format and BAS Digisim file for cyclic and linear sweep voltammetry txt These data files are in ASCII format and are stored in the data directory 112 User Manual GPES for Windows Version 4 9 Project files containing command lines for automatic processing of measurement procedures and data analysis mac These data files are in ASCII format and are stored in the data directory Print template files def These data files are in ASCII format and are stored in the Autolab directory File containing anodic and cathodic charges in cyclic voltammetry q amp q These data files are in ASCII format and are stored in the data directory The GPES executable file gpes4 exe The GPES binary help file gpes40 hlp The system parameter file ASCII format sysdef40 inp Description file of sysdef40 inp ASCII format sysdef40 txt Fit amp simulation parameter files efs Appendix II Definition of procedure parameters 113 Appe
114. ines to describe the experiment These lines are the same as the ones displayed above the plot Type of signal CV CM Aux signal Signal measured on selected ADC channel Charge Calculated charge Potential Measured potential Current Measured current ESPR Measured response from ESPR device pH Measured response of the pX module converted to pH see Utilities menu Calibrate pH electrode Measured response of the pX module px In galvanostatic cyclic voltammetry or galvanostatic chronopotentiometry potential should be read as current and vice versa Appendix II Definition of procedure parameters 125 Use ADC750 CV CM When the ADC750 module for fast AD conversions is present in the Autolab instrument it can be used for fast CV or chrono measurements if an interval time is smaller than 100 us Use boundaries for Q Q calc CV If checked this option enables the user to set potential boundaries for automatic charge calculation Between the first and second potential boundary the total positive and total negative charge will be calculated automatically Charge values are displayed in the status bar at the bottom of the screen The option is mainly used for Cyclic Voltammetric Stripping in electroplating research If this option is not checked the First and Second vertex potential are used as potential boundaries Use dynamic R compensation CV CM interval times gt 1s This op
115. ing Automatic and Linear baseline in the Options gt gt window Click search and have a look at the results 5 Close the Peak search results window and choose Window and Analysis results from the GPES manager bar In this window all the data analysis results are kept as long as you do not exit the GPES software Please check under File that you are able to Save Print or Clear the results Close the Analysis results window 6 Under Edit data choose the option Subtract disk file Select the same file that has been loaded democv01 Note that as might be expected the result is a horizontal line at I 0 By selecting Plot and Resume the original curve is retrieved This option always allows you to get back to the original curve after editing or analysing the data 7 Under Edit data choose the option Baseline correction Select Linear baseline at the settings and press Set markers You are now asked to set two markers for the baseline you want to correct Set the markers on the horizontal part of the forward curve before the peak and press OK Note that the Data presentation window now shows you both the original and the corrected curve in black By clicking OK you accept the corrected curve and the original is removed from the window Using the Resume option however gives you back the original 8 The option Wave Log analysis un
116. ion of a corrosion rate Before you start make sure that the method is still Cyclic Voltammetry Normal 1 Load the datafile democv02 from the autolab testdata directory 2 In the Data presentation window double click the vertical axis The vertical axis window appears 18 User Manual GPES for Windows Version 4 9 Fig 8a Vertical axis window Intercept position Min axis range Ticks O Major Scale Linear O Ln O Lg O Square root O 1 Square root Oy Ov Square root X O Minor Position Confirmation LINE ATTRIBUTES 3 Change the scale from the axis from linear to Lg i e 10log Please note that you are also able to change the range of the axis and the position of the intercept of the axis in this window Close the window and note the change of the curve 4 From the Analysis menu choose Corrosion rate The Corrosion rate window appears Chapter 2 Getting started with GPES 19 Fig 9 Corrosion rate analysis GPES Manager Manual control 5 x Fi A tilities O s Window Help 5 gt i al F JZ 2 JI Linear sweep voltammetry staircase Normal Procedure Democv02 File Copy Plot Analysis Editdata Work scan Iron screw in seawater Corrosion rate analysis 3 1 000x10 T 1 000x1044 1 000x10 4 1 000x10 3 7 Jal Corrosion rate Fit Tafel Slope Commands 1 000x10 4 i corrosion 1
117. ion on part of the voltammogram See Set window option of the Plot menu It is recommended that the cyclic voltammogram starts at zero current This can be achieved by performing a baseline correction 5 12 iR drop correction iR drop correction allows for software correction of the potential data for the Ohmic drop in the solution This option can be used for data from cyclic and linear sweep voltammetry After supplying a value for the solution resistance the measured and corrected curve are shown The question appears whether the data are corrected Appendix GPES data files The following types of files are used by GPES A display settings for cyclic and linear sweep voltammetry chronomethods voltammetric analysis multi mode electrochemical detection potentiometric stripping analysis steps and sweeps electrochemical noise Appendix I GPES data files 111 ici ixi jei idi ipi ifi ini These data files are in ASCII format and are stored in the procedure directory and in the data directory Experiment parameter settings for cyclic and linear sweep voltammetry chronomethods voltammetric analysis multi mode electrochemical detection potentiometric stripping analysis steps and sweeps electrochemical noise icw iXw iew idw my ifw inw These data files are in ASCII format and are stored in the procedure directory and in the data directory Measured data files for cyclic and l
118. is such that the surface concentration of the compound is kept zero the current can be described using Cottrell s equation i nFAD Cr f eq 9 where n is the number of electrons involved F Faraday s constant A electrode area D and C the diffusion coefficient and the bulk concentration of the compound respectively and time from the beginning of electrolysis Integration of this equation leads to the expression for the charge i nFAD Cr f eq 10 Semi integration of eq 9 or semi differentiation of eq 10 leads to the formula m nFAD C eq 11 In case of additional contributions enhancing the transport due to for instance spherical diffusion or a kinetic effect the semi charge is greater than predicted from the purely linear model and the line displays positive bias The inverse effect appears when the transport is slower than for limited diffusion or if the reagent is strongly adsorbed on the electrode There are a number of experimental problems that should be mentioned here First the data used for studies of transport phenomena should be corrected for the background otherwise deviations from linearity of the graphs can have other reasons In case of kinetic control of the process the time scale of the experiment also 108 User Manual GPES for Windows Version 4 9 determines the range of reaction rates and equilibrium constants that can be detected The quantitative discussion of influences of different exp
119. ivative is obtained from a 2nd order polynomial fit through the corrosion potential and its neighbours From this Rp value the corrosion rate can be obtained 72 User Manual GPES for Windows Version 4 9 Icorrosion B Rp where B is normally an empirical constant B can also be obtained from the Tafel slopes M Stern and A L Geary J electrochem Soc 1957 104 56 After clicking the Tafel slope button the Marker window appears Now the Tafel line for cathodic branch has to be defined by marking two points After the OK button on Marker window has been clicked the same has to be done for the anodic branch After the Tafel lines have been set a second Corrosion window appears with the results 1 The corrosion current corrosion current density and the corrosion rate 2 The Tafel slopes b and be 3 The corrosion potential at zero current and the corrosion potential as calculated from cross point of the two Tafel lines 4 The Polarisation resistance Rp obtained from the equation 1 ca 1 Rp B icomosion Where B andS 2 303 S by be J Fig 49 Corrosion rate analysis GPES Manager Manual control 5 x File Method Utilities Options Project wi Help JLL Linear sweep vollammety staircase Nomal Procedure Democv 2 Data presentation File Copy Plot Analysis Edi data Work scan Iron screw in seawater Corrosion rate analysis ST 1000x104 1 000x10 4 1 000x10 4
120. ive channel number is set to 1 46 User Manual GPES for Windows Version 4 9 Please note The last 2 commands are available in the GPES and FRA programs However for FRA projects that are called from within GPES projects all channel switching commands in the FRA project scripts are ignored In such cases the GPES project will have exclusive control over the channel selection Utility Delay lt n gt hold the project for lt n gt seconds Repeat lt n gt EndRepeat with the Repeat and EndRepeat commands it is possible to repeat a part of the project lt n gt times You can nest these commands maximal 5 times ForAllChannels lt filename gt gt executes the active measurement procedure for all available MUX channels and store the results in the lt filename gt adding 3 characters to the filename as channel number counter for example fname001 fname002 etc DIO SetMode lt Connector gt lt Port gt lt Mode gt set the mode of a port of the DIO DIO SetBit lt Connector gt lt Port gt lt n gt lt Bit gt seta single pin of the DIO on or off DIO SetByte lt Connector gt lt Port gt lt n gt seta port of the DIO to the specified value DIO WaitBit lt Connector gt lt Port gt lt n gt lt Bit gt wait until a single pin of the DIO is set on or off DIO WaitByte lt Connector gt lt Port gt lt n gt wait until a port of the DIO is set to
121. l bz Data pres Ef Paint Shop Prol 2 Screen Capt 2 46 PM Chapter 3 The GPES windows 59 Some sub options require explanation Automatic This option automatically rescales the data during a measurement Resume The Resume option makes a fresh copy of the measured data into the Data presentation window This allows you to get back to the original data after doing data analysis Zoom Clicking the Zoom option has the same effect as pressing the right mouse button When this option is activated a magnifying glass appears When subsequently the left mouse button is clicked and held down a Zoom window can be created Set window The Set window option allows to define a part of the data set Any further data manipulation and display will be applied to this part of the data With Chrono methods the x values will be normalised to 0 so the x axis always starts at t 0 First and Second signal The First and Second signal options are selectable when next to the current or potential signal a second signal is recorded A marker in front of these options means that they are displayed When both are displayed no further data analysis is possible E vs t plot and dt dE vs E plot These options appear only when the method is Potentiometric stripping analysis It allows switching between these types of plots The E vs t plot can be used to do Transition time analysis see the chapter on the analysis of measured data in order to analyse th
122. l start making a graph of the current versus time Switch the clock off again and use the window below the slider to set a potential of 0 V Switch the cell off again 14 User Manual GPES for Windows Version 4 9 2 3 Data manipulation of a cyclic voltammogram 1 Choose File and Load scan and load the datafile democv01 in the autolab testdata directory Enlarge the graph by clicking the maximise button on the Data presentation window 2 Double click the curve in the Data presentation window A plot parameter window appears in which you can change the colour of the curve or change from a line display to a scattered display Please try this by changing the colour and the style of the line Select the settings that you feel are the most suitable for this curve 3 With the peak search option the software allows you to determine all peak parameters of the CV Choose Analysis and Peak search When the Peak search window appears click the Options gt gt button the program now allows you to set a number of options Start by selecting Curve cursor and Lin front baseline click close and press the search button in the Peak search window You are now asked to set two markers for a baseline in front of the peak please do so and press OK The program shows the result of the peak search in the Peak search results window and shows the peak in the curve 4 Please repeat the above after select
123. l window When Switch iR compensation off at current overload is checked the cell will be switched off when the current exceeds about 8 times the current range value This normally occurs when the potentiostat oscillates because the compensated resistance is too high WARNING Too high Ohmic drop compensation can cause oscillation of the potentiostat which may cause damage of the working electrode fig 22a Effect of overcompensation of the iR drop Data presentation _ x File Copy Plot Analysis Edit data Positive Feedback 7 5m i 1 Y pulse on dummy cell c 5 0m4 zan Wy lt 0 2 5m4 Ru 108 Ohm 5 0m7 7 5m r r T T r T T 0 2 5m 5 0m 7 5m 10 0m 12 5m 15 0m 17 5m 20 0m tis Calibrate pH Electrode This window allows to calibrate pH electrodes It is possible to specify two buffer solutions and the calibration temperature Measuring the pH as a 2 Signal gives the possibility to specify a measurement temperature The pH is corrected for temperature 40 User Manual GPES for Windows Version 4 9 Fig 22b The Calibrate pH Electrode window pH Calibration Current pH measured E 0000 y pH 7 00 Drit 0 000 pHunitsis Calibration Settings pH Buffer 1 7 00 0001 Y Accept pH Buffer 2 4 00 A y Accept Buffer temperature 298 0 K OK Cancel When the value for a pH buffer is Ok press the Accept button The OK button will actuate the cal
124. le menu of the Data presentation window in a work data file This file cannot be distinguished from the files with measured data Both types of files have the same format and layout Some care should be taken with saving the work data For example as is described further on the display of the current values can be changed to a square root of the current If the work data are then saved not the current values but the square root of the current is saved Chapter 3 The GPES windows 57 On the message line at the bottom of the graphical display important text about the required user actions during analysis of editing data appears If no message is displayed the currently measured potential and current are displayed File The file option allows to create data files based op on data presented in the Data presentation window It allows to save the so called work data file as discussed above The following options are available Save work file This option was discussed above Save I forward and Save I backward The Electrochemical techniques Square wave Differential pulse and Differential Normal pulse provides the forward and backward current data These curves can be plotted but not analysed The separate curves can be stored and retrieved with File Load data from the Gpes manager window to do analysis Save impedance data When an AC voltammetry measurement is done the impedance data for each data point can be saved to disk
125. le Method Utilities Options Project Window Help AE joj gt ul JAHA Chrono methods interval time lt 1 s Amperometry Procedure DEMOCX01 Linear regression Data presentation File Copy Plot Analysis Editdata Results Commands Slope 9 827E 7 begin s d 7 396E 10 Y begin 1 1 Slope 1 018E 6 end Intercept 2 125E 8 Y end s d 7 146E 9 No points Chi square 1 107E 13 Corr coeff Close 30 40 t s 1 Square root Status Messages Disk file Analysis Linear regression HA Start AY Exploring P Bl cres Mana C Manual control A Data pres ES Paint Shop Prof E1 Edit procedure 11 30 AM 4 From the Plot menu choose Resume and the original curve will reappear 2 7 Data analysis with differential pulse voltammetry From the Method menu choose voltammetric analysis and then Differential Pulse 1 Load the datafile demoea01 from the autolab testdata directory 2 From the Analysis menu choose Peak Search Under the options choose the automatic search close the Options window and press the search button The Peak search results window will now show parameters for four peaks For the first three the results are reasonable but for the peak at the highest potential the linear baseline is not the best option 3 With the Set window option under the Plot menu you are able to extract the last peak from the curve Set the markers so that only the last
126. le is stored is called the procedure directory When the directory in the Open procedure window is changed and a procedure file is 28 User Manual GPES for Windows Version 4 9 successfully loaded from this new directory this new directory becomes the new default procedure directory Normally only files with the current method are shown in the load window By selecting Show all GPES files in File dialog box Utility menu all procedures are displayed and can be selected It is also possible to load procedure files from the DOS version GPES 3 If this is required click the List Files of Type drop down button and select the proper option It is also possible to load a procedure from other methods techniques than the current one The program will change automatically to the method described in the selected procedure See the Dropdown menu called List Files of Type Save procedure This option will save a procedure under its current name in the procedure directory Save procedure as Allows to store a procedure on disk in the procedure directory with a different name as the current one Please use the default file extension as mentioned in File name field or omit the extension In the latter case the correct extension will be added Print The Print menu window appears after selecting this option The Print select panel allows to choose between the print out of the measured data a dump of a window and the print of a template consisting of
127. line O Linear baseline O Exponential basecurve Polynomial basecurve O Lin front baseline O Lin rear baseline O No baseline Close Peak search Curve cursor Whole peak Polynomial basecurve_ Options gt gt Close Search lp Show results IJA 0 20x1074 0 18x1074 0 15x107 4 0 13x107 0 10x1074 0 08107 0 05x107 4 0 03x107 4 Messages Da Disk file Analysis Peak search 2 8 Analysis of Electro Chemical Noise HA Start LA Exploring Psp E ares Manager Manual control lA Data presentation ES Paint Shop Pro El Edit procedure a 11 38 AM From the Method menu choose Electrochemical noise and then Transient Load the datafile demoecn1 from the autolab testdata folder From the Analysis menu choose Spectral noise analysis Choose a Hanning Window check subtract offset and the Result type E f and 1 2 3 I f By clicking OK a spectral analysis is performed on the Potential and the Current components of the noise signal Chapter 2 Getting started with GPES 23 Fig 13 Example Electrochemical Noise analysis GPES Manager Manual control File Method Utilities Options Project Window Help 2 4122 gt ul aj 418 2 Electrochemical noise Transient Procedure OLD5 Data presentation File Copy Plot Analysis Editdata Electrochemical
128. ll consist of two pages The Manual control window which manually controls the settings of the potentiostat galvanostat The Data presentation window which gives a graphical display of the measured data and allows you to do data analysis and or modification The options and possibilities of these three windows will be explained in detail in the next chapter 2 1 Recording a cyclic voltammogram with the dummy cell 1 Before starting with this and with the other examples please check the hardware configuration of your system You can do this by executing the hardware configuration program In the Autolab hardware configuration window you can check if all the modules in your instrument are also selected in the software if so you can close this window by clicking OK See also the Installation and diagnostics manual 2 From the Method menu of the GPES manager bar please select Cyclic voltammetry staircase Normal 3 Select Open procedure from the File menu and open the testcv icw from the autolab testdata directory Fig 2 The Open procedure window Open procedure Cyclic and Linear sweep voltammetry EA ES Look in E TestData E Al ex fe Democv01 icw fan Testbpot icw an Testscan icw an DemocvO2 icw lam Testbstr icw T stfi20a icw aa DemocvO3 icw Testcv icw laa Tstfi20b icv aa DemocvD4 icww fas Testev6 icw m DemocvO5 icw m Testecd icw sa Hydrodyn icw m Tests_a icw
129. ls this is of course not true Therefore for some cases it would be advisable to apply a so called 74 User Manual GPES for Windows Version 4 9 Window function These operations will counteract the effects that were mentioned above A total of 5 functions are available none Bartlett Hanning Hamming Blackman A range of literature is available on the theoretical background of signal processing See Numerical Recipes W H Press et al Cambridge University Press Cambridge 1997 4 10 Find minimum and maximum The Find minimum and maximum option shows the minimum and maximum Y value with their corresponding X values 4 11 Interpolate The Interpolate option allows the user to calculate one or more X values or Y values which corresponds to a given value on the other axis A linear interpolation is used to calculate intermediate values 4 12 Transition time analysis The Transition time analysis option only appears for chronopotentiometric data or data from Potentiometric stripping analysis The background of this analysis is fully described in the book of C M A Brett and A M O Oliveira Brett Electrochemistry Oxford science publications ISBN 0 19 855388 9 After selecting this option a graph of the time versus potential is presented and the user is asked to specify two marker points for subsequently the baseline the transition line and the limiting line The time difference between the crosspoints of the transition line
130. lso the fitted values of interdependent parameters are meaningless or the program oscillates and it cannot deliver the final values Finally the computational time unnecessary increases because fitting of each parameter requires the calculation of the derivative of the fitted curve with respect to this parameter Some derivatives can be calculated analytically but some not and in the latter case the derivative must be obtained numerically This requires an additional simulation per iteration step Fit and simulation error messages error 1 XXXXXXX Internal error of the fit and simulation program String xxxxxxx contains specific information about the problem Please report circumstances under which this error appeared error l Not enough memory There is not enough memory available to carry out the simulation Try to free some memory by closing other applications error 10 Technique not supported An operation has been requested that is not supported for the currently selected technique Please report circumstances under which this error appeared error 11 Mechanism not supported An operation has been requested that is not supported for this electrode reaction mechanism Please report circumstances under which this error appeared Chapter 4 Analysis of measured data 85 error 12 Model not supported An operation has been requested that is not supported for the model chosen Please report circumstances under which
131. meter determines the width of the window which moves through the data set Peaks with a width at half peak height which are smaller than the specified peak width might not be found It is possible to find peaks that are present as shoulders on a steep base curve For this purpose the Peak search option contains an Include shoulders option The option is found at the Peak search options window and can be selected only in automatic search mode When this option is clicked on the Peak search is performed after a basecurve correction on the background according to the moving average baseline correction 66 User Manual GPES for Windows Version 4 9 method This method can also be performed separately See Baseline correction option in the Edit data menu Fig 42 Peak search window Peak search Automatic Whole peak Linear baseline Show results Fig 43 Peak search options window Peak search options Search Peak Baseline FP Reverse Automatic Whole peak O Linear baseline pese O Front peak O Exponential basecurve snoulders O Free cursor O Rear peak O Polynomial basecurve Lin front baseline Minimum Lin rear baseline Set formats a Close Peak height 1 0E 10 O No baseline Fig 44 Set results format window Set results format Y Data Decimal Scientific Precision 2 X Data Decimal O Scientific Precision a
132. mi integral A B As the convolution of the voltammetric current with a t function semi integration produces a value proportional to the surface concentration of the product of the reaction the convoluted value should return exactly to zero after completion of the cycle which means that the product of the reaction has been entirely converted back to the substrate If it does not return to zero the consumption of the initially present substance is suggested It should be stressed however that this method requires diffusion to be semi infinite and linear In situations where this is not the case corrections have to be made Such a correction is available S O Engblom K B Oldham Anal Chem 62 1990 625 for F E Woodard R D Goodin P J Kinlen Anal Chem 56 1984 1920 I D Dobson N Taylor L R H Tipping in Electrochemistry Sensors and Analysis M R Smyth J G Vos eds Elsevier Amsterdam 1986 106 User Manual GPES for Windows Version 4 9 spherical electrodes mercury drops under the name of spherical convolution it requires the values of electrode radius and of diffusion coefficient delivering the concentration of the reaction product on the surface of a spherical electrode If the presence of an irreversible homogeneous reaction is detected its rate can be measured For this purpose a so called kinetic convolution can be used In this transformation the effect of consumption of the product by the r
133. ndix II definition of procedure parameters CM Chronomethods CV Cyclic and linear sweep voltammetry ECD Electrochemical detection ECN Electro Chemical Noise PSA Potentiometric stripping analysis SAS Steps and Sweeps VA Voltammetric analysis ADC channel number Second signal CV CM The channel number which should be used for recording the output from an external source Amplitude VA ac voltammetry The root mean square value of the applied potential sine wave perturbation Amplitude VA square wave Half of the peak to peak value in the squared wave perturbation Base potential VA normal pulse differential normal pulse The base potential level The pulse will be superimposed on this potential level Begin potential CV linear sweep The potential at which the ramp starts Cell off after measurement All If not checked the cell switch will be left in the on position after the measurement procedure has been completed The applied potential is the stand by potential Comment All A panel to type in several lines of text Conditioning potential VA This is the first potential applied after the start of the procedure This potential is normally applied to clean the electrode surface This potential is not applied when its duration is set to zero Correct iR drop during dyn iR CV CM with dynamic iR compensation If checked the potential will be corrected for the ohmic drop If not
134. ng Initial guess from the Option menu Check whether the number of exchanged electrons is correct Select parameters to fit by checking the boxes next to parameter names If necessary adjust the starting value of parameters by clicking it with the mouse pointer and entering the new value make sure that the number of electrons is set to 2 If necessary switch to extended setup Option menu or Ctrl E to edit other parameters or to change parameter s convergence criteria Parameters that are visible in the extended setup but invisible in the standard setup are not fitable i e their values are not changed during the fit process see Fitting choosing parameters to fit and Fitting convergence criteria for more detailed information Select Full Fit control parameters from the Option menu and adjust their values see Fitting advanced options for details Click Fast Fit button on a reduced number of data points The fitting proceeds until the convergence criteria are satisfied or the maximal number of iterations is reached whatever comes first It is possible to stop fitting at any moment by clicking Stop fit button It is possible that the program will need a few seconds to complete the iteration before stopping During the fit the field Status shows the number of the iteration field Chi square shows the x value and field Elapsed time shows time elapsed from the start of the fit If convergence is reached the Status field co
135. ns because the term an is fitted as a whole The characteristic potential E is defined as E RT anF nk E RT amF ink where ky k t Dz and k k t Dp ks and km are the electron transfer rates used in Butler Volmer equation I k cp expl anF RT E k c exp onF RT E E Differential pulse voltammetry reversible electrode process followed by irreversible chemical reaction ECi Reaction equation R gt P RS B Fitable parameters redox potential E V normalised forward chemical reaction rate kc foll gt norm ky peak current Jp A constant background current A Initial guesses available for Ep Ip background current Chapter 4 Analysis of measured data 93 Comments The forward chemical reaction rate is normalised with respect to the time scale of the voltammetric experiment ky kptm No simple expression is available for the peak height Square wave voltammetry reversible electrode process Reaction equation REE P Fitable parameters formal potential E V peak current J A constant background current A Initial guesses available for Ep lp background current fitting on net current Ept Jp background current fitting on forward backward current Comments There is no simple expression for the net peak current The interpretation of the value of J depends whether fitting takes place on the net current or on forward backward currents in the first case Ip corresponds to
136. ns can be clicked Off 5s 1s 1s The effect of a filter constant of e g 5s is that 5 seconds after a potential perturbation has been applied the current response can be measured correctly The Remote led indicates when it is possible to edit the parameters in Manual Control In cases where it is red it is not possible to edit the parameters in this window 3 4 Data presentation window The Data presentation window serves several functions display of data data analysis data manipulation communication with other programs like Paintbrush Excel or MS Word The window consists of a menu bar a graphical display and a message line As mentioned earlier the measured data are kept in a shared data memory block with the data acquisition software During the measurement the measured data points are also copied to the memory block of the Data presentation window After the measurements the data in this memory block can be modified by options in the Data presentation window However it is always possible to resume the measured data Note that the save options of the File menu of the GPES Manager window always save the measured data Also note that for cyclic and linear sweep voltammetry during the execution of a procedure the measured data are plotted but after the measurements only the last measured scan is visible The data which can be modified in the Data presentation window are called work data and can be stored from the Fi
137. ntains information ready and the number of iterations If the maximal number of iterations has been carried out without reaching the demanded convergence criteria values the status field displays information stopped and the number of iterations If fit has been stopped by Stop fit button the status field displays information interrupted Pressing Full Fit starts the new cycle of fitting taking all data into account with as start values the values visible on the screen The number of iterations and the elapsed time counter are reset Fit parameters can be saved using option Save fit parameters and reloaded using the option Load fit parameters both options from File menu To replace the work data by the fitted curve use Make work data option from the File menu To quit the fit window click the Close button press Alt C or select Close from the File menu During fitting the results of each iteration are shown in the Data Presentation window together with the original data set It is possible that some iterations will go in the wrong direction delivering worse approximations than the previous one In this case the fitting procedure steps back and tries to obtain another better approximation The process of stepping back can take few iterations during which curves observed on the screen may differ severely with the analysed data However this is not a reason to worry as the fitting procedure finally comes with a better approximation
138. o save the previously measured scan This option can also be activated by typing SAVE on the keyboard The path and the name of the file can be specified as the Direct output filename The last five characters of the file name will be used as the scan number Record Bipotentiostat signal bipotentiostat CV CM The input parameter only appears when the Autolab is equipped with the bipotentiostat module Record second signal CV CM The primary signal current or potential is sampled via one of the channels of the ADC164 or ADC124 analog to digital converter module If Record second signal is checked the voltage level of an additional channel of the ADC164 or ADC124 module is sampled as well The channel number can be specified The ADC164 or ADC124 module has 16 input channels which can be recorded An internal multiplexer allows switching from one channel to another Four of them have an external BNC plug Normally input number three and four are free channels i e not used by GPES They can be used to record the output of another instrument In galvanostatic cyclic voltammetry or galvanostatic chronopotentiometry potential should be read as current and vice versa 120 User Manual GPES for Windows Version 4 9 The input parameters related to the second signal do not appear when the Autolab is equipped with a bipotentiostat module Reverse scan for i gt CV If Specify current boundaries is check
139. ocedure DEMOCV01 voltammetry staircase Normal we a 3 inual control Cyclic voltammetry linear scan Stationary current Linear sweep voltammetry staircase Scan averaging Current integration Cell off Chrono methods interval time gt 1 s pa saree 4 J gt A gt Galvanostatic Chrono methods interval time lt 1 s Fest scan High Sens off 000 v 0 Multi mode electrochemical detection a Pe 100uA High Stability Potentiometric stripping analysis HIDUA Current Potential Steps and sweeps RIA Potentiostat AAA F 100nA Electrochemical noise 9 Fi0nA iB comp off Settings Potential iR compensation O Time Pe Potential Hea Remote E o Cell off after measurement ETE noise Clock off A Standby potential V Number of scans Data presentation Potentials File Copy Plot Analysis Editdata Work scan Define start potential w r t OCP F Ferri Ferro Start potential V 398 Cyclic voltammetry First vertex potential V 6 Second vertex potential V 4 0 100x10 Step potential V 00244 ore Scan rate V s 099992 y 0 100x10 0 300x10 0 500 0 300x10 0 250 E V 0 500 Title and subtitle fr Status Messages Disk file Q 1 543E 03 C Q 9 369E 04 C Manual control HA Start ay Exploring P E cres Man C Manual control
140. ode which is connected via an IME interface to the Autolab The stirrer can be switched on and off the purge valve can be opened and closed and a mercury drop can be created The Reset button will reset the digital I O port of the Autolab instrument The Purge and Stirrer will be switched off This option is not accessible when no static mercury drop electrode is connected to the Autolab 34 User Manual GPES for Windows Version 4 9 Fig 18 The Electrode control window Electrode Control New drop Burette control The burette control option allows to control motorburettes connected to Autolab via the DIO48 module Consult the Installation and Diagnostics guide about the type of burettes that can be connected First click the Setup button Then select the burette Fig 19 The Burette control window Burette control 0 Step dose Dosed volume Select burette Step P 05 ml O Burette 1 0000 mi Dose y Continuous dose Functions Speed 0 1 ml s Fill Burette Flush Burette ii Dose on No of flushes 1 Setup gt gt Close The displayed Burette setup window allows to define the connected burette Please consult the manual of your burette for the parameters Reset E Chapter 3 The GPES windows 33 The Maximum time to check for Ready is the maximum wait time for the software to receive a ready signal from the bu
141. ogram presented in the appropriate figure Fig 55 Peak artefacts in semi derivative voltammetry The curve in the above mentioned figure is the result of semi differentiation where two peaks appear one in the forward and one in the backward branch The second semi derivative peak does not represent any hidden voltammetric peak but is an artefact resulting from semi differentiation of a wave like current decay Such a peak can only appear in the backward branch of semi derivative voltammograms and has characteristic features in the potential range where such a peak appears 1 there is no backward voltammetric peak ii there is a forward peak and 111 the sign of SCV current values is the same in both branches All peaks that satisfy these criteria are probably artefacts The third limitation of the method stems from the fact that results presented in the above mentioned figure concern an uncomplicated electron transfer under semi infinite linear diffusion conditions The form of the peak is different when the mechanism of the reaction and the transport type change usually peaks become less symmetric and broader resulting in a decrease in separation capability and in certain situations leading to deformations of neighbouring semi derivative peaks Determination of formal potential and the number of electrons involved The equation 5 describes the form of a semi derivative voltammetric peak in a case of uncomplicated fast electron t
142. ollowing a straight line to the beginning time is zero the iR drop is calculated Since the current is measured just before switching off the cell the uncompensated resistance is calculated It will be clear that for a proper calculation of the uncompensated Ohmic resistance Ru the current must be known very precisely Proper measurement must be done at a potential where the current is high enough to be measured and the applied current range must be adequate to measure the current For proper measurements the current must be at least in the order of 1 mA Also make sure that the current at the applied potential before the current interruption can be measured sufficiently accurate Therefore select a proper current range which means that the current should be in the order of the selected current range It is recommended to switch off the iR compensation see Manual control window In order to get an accurate value for the uncompensated Ohmic drop the I interrupt measurements should be done at the highest possible speed If an ADC750 module is present in the Autolab system it is possible to use this module in order to speed up the measurements to 750 kHz Before measuring you need to specify the potential range at which the I interrupt is performed If the potential is within the limit of 1V to 1V specify 1 V range If the potential is outside this range specify 10 V range On the iR compensation window that appears several parameters n
143. olor White Je 20 0 Height 60 0 J Border E Confirmation Double clicking the axis itself allows scaling and positioning of the axis and selection of the axis function Data can be displayed among others as linear inverse log natural log square root inverse square root Except for the linear and og the value Chapter 3 The GPES windows 63 of the presented data is modified in real So all subsequent operations are really performed on e g the square root of the data In case of the og not the values but the axis is changed to a logarithmic axis When the button 1 in the upper right corner is clicked the Graph parameter window appears This window allows modification of the relative scale parameters of the so called graph and plotting area and their background colours All the changes made to colour and sizes are stored in the default graphics display file The other changes are kept in the procedure file 3 5 Edit procedure window The Edit procedure window consists of 2 pages In Page 1 the most common parameters can be specified Page 2 contains the other parameters The meaning of each parameter is clarified by the Help program A list of parameter descriptions is given in the appendix about this subject In the option bar the Send option is displayed This option can only be clicked during the execution of a measurement procedure It is relevant when a parameter is changed The Send option activates the
144. peak is visible Now there are two options please start each option after setting the window around the last peak a From the Edit data menu choose baseline correction and select the polynomial basecurve Click the set markers button and set the markers for the baseline one on each side of the peak After OK the corrected black curve is shown with a more horizontal baseline You can now use the automatic peak search option to find the 22 User Manual GPES for Windows Version 4 9 peak parameters Please do so and check the difference with the automatic search on the non corrected curve by opening the Analysis results window b From the Analysis menu choose the Peak search option Under options choose curve cursor with a polynomial baseline After pressing the Search button you are asked to set two markers for the baseline please do so Now the Peak search results window will give you the parameters of this search Please open the Analysis results window to compare this option with the result of option a As should be expected the results of these two options are very similar Close the Analysis results window Peak search options Fig 12 Example of polynomial baseline correction _ 5 x Search Peak Peak height 1 0E 10 Reverse Automatic Whole peak 4 F Include Curve cursor O Eront peak shoulders O Free cursor O Rear peak Minimum Peak width 03 Base
145. r plotted on the screen and stored in the computer memory Also the data file becomes too long to be loaded by the GPES program Direct Output filename CV The path and the name of the file The last five characters of the file name will be used as the scan number This filename will be used for the Save every nth Cycle option Duration of Measurement ECN The total duration of the Measurement It will be rounded to the next nearest power of 2 times the Interval time Dynamic iR amplitude CV CM interval times gt 1s The amplitude of the square wave in Dynamic iR compensation End potential CV linear sweep SAS The potential at which the ramp stops Equilibrate with potential pulses ECD If checked the specified potential pulses are applied without recording data otherwise the stand by potential is applied Equilibration time All The time to equilibrate the electrode at the start potential CV VA or the stand by potential CM ECD PSA Equilibration threshold level VA CV CM ECD If enabled the Equilibration stage will be aborted after reaching this specified current The measurements will start as soon as this threshold value is exceeded This option is not available for galvanostatic measurements Final rotation speed rpm LSV staircase hydrodynamic The rotation speed applied during the last scan First conditioning potential CV CM ECD The first potential which is applied after the
146. ransfer under semi infinite linear diffusion transport It is clear that the peak potential is equal to the formal potential of the reacting system and for cyclic voltammetry that both anodic and cathodic peaks appear at the same potential This feature can be used as a simple and rapid test for reversibility of the reaction This test is superior to the well known test based on the difference of potentials of voltammetric peaks as it does not require knowledge about the number of electrons involved If the rate of electrode reaction is limited by the diffusion or by kinetics of the electron transfer the number of electrons involved can be determined from the half width of the semi derivative peak This half width should be Chapter 5 Editing of measured data 105 w 3 53RT nE eq 7 for a diffusion controlled process and w 2 94RT anF eq 8 for a rate controlled process Irreversible homogeneous reaction consuming the product of the electrode process The criterion for the absence of an irreversible homogeneous reaction is restoration of the initial state at the electrode surface after a cyclic change of electrode potential If such a reaction does not occur the surface concentration of all species after the experiment should be exactly the same as before Fig 56 Semi integration of voltammograms in case of the absence A and the presence B of an irreversible homogenous reaction Thin line voltammogram thick line se
147. rette The DIO port used is shown on your Autolab front The Dose button will dose the amount specified above The dosed volume is displayed The Dose on button will dose with the speed displayed above The Reset button will give a reset command to the burette and sets the dosed volume to zero RDE control In order to control an external Rotating Disk Electrode RDE an option is available in the Utilities menu of the GPES manager In Hardware configuration an external RDE should be specified After selecting the RDE control item the following window appears Fig 20 The RDE control window fm RDE control Rotation speed r p m 1000 0 rpm 04 72 rad s Setup gt gt Close With the scroll bar it is possible to control the rotation speed of the RDE You can also enter the number of rotations per minute by changing the r p m edit field or enter the rotation speed in radials per second in the rad s edit field After pressing the Setup button the RDE setup window appears 36 User Manual GPES for Windows Version 4 9 Fig 21 The RDE setup window m RDE Setup _ Oy x RPM per Volt boo rpm Maximum rotation speed 3000 r p m DAC channel 3 or 4 3 Warning Select DAC channel wih care DAC channel 3 may be in use by the BIPOT ARRAY or ECD module Do not use these modules together with RDE control DAC channel 4 may be used for AC voltammetry and may therefore result in w
148. reversible electrode process Reaction equation R gt P Fitable parameters halfwave potential E V limiting current jim A constant background current A Initial guesses available for number of exchanged electrons Ein him background current Comments The theoretical expression for the limiting current at a large flat electrode is Lim N FAComkDg Tt P where t is the pulse time The halfwave potential should be equal to polarographic halfwave potential Normal pulse voltammetry quasi reversible electrode process k Reaction equation R P Fitable parameters redox potential E V Log normalised electron transfer rate log k transfer coefficient a limiting current Jim A constant background current A 90 User Manual GPES for Windows Version 4 9 Initial guesses available for namber of exchanged electrons E Inorm background current Comments The parameter loglk is a 10 base logarithm of the electron transfer rate normalised with respect to the time scale of the experiment k k it D where tp is the pulse time and k is the electron transfer rate used in Butler Volmer equation I k e exp onF RT E E c exp 1 onF RT E E The theoretical expression for the limiting current at a large flat electrode is Ltim N FA Cpu D Ttp la Normal pulse voltammetry irreversible electrode process Tks Reaction equation R 5 P Fitable parameters Characteristic potential E V Log
149. rintout of the graph You can include the Analysis text as follows You can select a part of the text Under the option Edit click the option Copy or Cut Now the text is present in the paste buffer Now select the Copy menu on the Data presentation window Select Paste text The text will be included into the graph Please note In the Data presentation you can drag the text to the position you want The text in Data presentation can not be changed but can be cleared by double clicking and typing in a space in the Text field You can also change the text style in the window For a proper outlined text a change to the font Courier is sometimes required Chapter 4 Analysis of measured data 65 4 Analysis of measured data Under the Analysis option on the Data presentation menu there are a number of facilities to analyse measured data Some analysis techniques are specific for an electrochemical method The results of the analysis are sometimes displayed in a specific window In all cases the results are printed in the Analysis results window This window can be made visible from the Window option on GPES Manager menu bar In most cases not all options are selectable This may have the following causes The option is not relevant for the electrochemical method The execution of a measurement procedure is in progress Another conflicting option is already selected Just after the recording of more than one cyclic or linear sweep vol
150. rong applied potentials on the potentiostat Contact your distributor if you need more information Cancel OK In this screen you can configure the RDE MUX control The channel number of the SCNR16A SCNR8A or MULTI4 module can be selected manually by the operator before starting the measurement procedure 1 Open the MUX control dialog by selecting MUX control from the Utility menu The dialog screen shown in the figure below will pop up Enable the checkbox Use Multiplexer Module Choose the desired channel Pressing lt Apply gt or closing the dialog screen will set the selected channel The active channel number will be indicated in the Manual control window i tS Fig 21a The MUX control window am Multiplexer control SCNR16A Currently selected channel 1 Select Channel 1 16 Chapter 3 The GPES windows 37 If you want to return to direct connections you can disable the Use Multiplexer Module checkbox l interrupt The I interrupt option provides a method to determine the Ohmic resistance of the cell This option is only available when the Autolab is equipped with a PGSTAT12 20 30 100 potentiostat galvanostat The technique involves switching off the current and measuring the potential time curve As soon as the current is switched off the potential difference across the Ohmic resistance is zero and the charged double layer is discharged By extrapolating the curve f
151. s easily visible when the simulation method is compared with analytical equations describing current potential curves which have a number of restrictions on their validity The fitting method Fitting is carried out using Marquardt nonlinear least squares method The model functions are either calculated from analytical equations wherever possible or obtained by digital simulation of the electrode processes The convergence criteria are based on the value of x EC Y Y o and its change during the last iteration as well as on the requested precision of the fitted parameters 76 User Manual GPES for Windows Version 4 9 Elements of the Fit and Simulation Window Fig 50 Fit and simulation window Fit and Simulation File Options Fit a Sinan Status Chi square Elapsed time s Mechanism Parameter Value Fit yn Process 1 reduction 1 oxidation 1 Number of exchanged electrons 1 EO v J x Normalized current 4 1 E 4 x Background current 4 x In the upper part of the Fit and simulation window there is the drop down menu with a list of available models five action buttons and two option buttons to switch between the fit and the simulation mode of the program The list of models that can be used depends on the experimental technique chosen The middle part of the window contains three display fields Init Guess button starts the calculation of the initial guesse
152. s of fitable parameters Fast Fit performs a fit on a reduced data set See the chapter Fitting in more detail about the data reduction and other fast fit parameters The Full Fit button starts a fit of the model on all data points This button is replaced by the Simulate button in case the simulation option is chosen The Stop Fit button will interrupt a running fit procedure Fields show the status of calculations the value of x and the elapsed time The lower part of the fit and simulation window displays the parameters Normally only fitable parameters are shown it is possible to display all parameters by choosing the Extended setup option from the Option menu Each line contains the name of the parameter its value and a checkbox to indicate whether the parameter should be fitted or not In extended setup in each line there are additional fields for the value and the type absolute relative or disabled of the convergence criterion Fitting and simulation step by step Fitting 1 Load acyclic voltammogram file C AUTOLAB TESTDATA DEMOCVO3 0CW 2 From Analysis menu Data presentation window select Fit and Simulation 3 Select the model reversible from the drop down menu in the top part of the appearing window 16 Chapter 4 Analysis of measured data 77 Make sure the switch right to the model name is set to Fit Get the initial guesses for the parameters either by clicking Init guess button pressing Alt G or by choosi
153. s the following extra items are available smooth level during differentiation of potential versus time data a number of comment lines A full list of input parameters is given in appendix II 3 6 Analysis results window The Analysis option of the Data presentation window allows the making of an analysis of the data In some cases the results are displayed in a special window which differs per analysis technique In all cases a report of analysis is printed in the Analysis results window The Analysis results window contains all the results of the analysis of the data Only when the GPES Manager window is closed the Analysis results window is cleared The File option of this window allows the user to clear save or print the content of the window The Edit option allows the user to remove Cut the selected part of the text Text can be selected by keeping the left mouse button pressed and moving it over the window The Copy option copies the content of the window to the paste buffer including a so called DDE link For example MS Word can via Paste special option makes a Paste Link This means that any change to the content of the window will automatically be copied to the MS Word document until the link is broken via the Links option of MS Word The Paste option will include text from the paste buffer It is possible to copy results of Analysis into the graph of the Data presentation window This is useful if you want to have a complete p
154. scan Smooth Change all points Delete points Baseline correction Subtract disk file Add disk file Subtract 2nd signal Ferri Ferro 0 400x10 0 300x10 4 0200x1074 Derivative Integrate Convolution Time semi derivative 0 100x10 4 iR drop correction Time semi integral East Fourier GO differintegration XA ERLT differintegration Spherical convolution Kinetic convolution 0 100x10 4 0 200x107 4 0 300x10 0 501 Status Messages Disk file Q 1 543E 03 C Q 9 369E 04 C Manual control Zz HA Start AY Exploring c BE GPES Mana Er Manual controll 0 130 0 E Screen Capt 1 Edit procedure E Paint Shop Pro 3 05 PM In a number of electroanalytical techniques the current measured displays proportionality to a 1 function The popularity of this type of dependence originates from the solution of Fick s law in the case of semi infinite linear diffusion the most common type of the transport of the reagent to the electrode According to this solution the gradient of the concentration of a substance consumed in the electrode process decreases with the square root of the electrolysis time and so does the current which is proportional to this gradient Such a dependence can be easily observed in chronocoulometry chronoamperometry and in voltammetry in this latter case in the descending branch of the peak Chapter 5 Editing of measured data 101
155. se without pressing a button The way in which the parameters are displayed may be changed by double clicking a field and choosing for example scientific and then setting a precision Precision 1 means that the value is printed with the format used in the Edit procedure window Close the Template window Chapter 2 Getting started with GPES Fig 8 Results of printing of the template Template C AUTOLAB1CY_POT1 DEF File Edit Insert 17 Title Ferri Ferro Subtitle Cyclic voltammetry Creation date 21 Oct 1994 Creation time 11 34 42 Pretreatment Purge time s 0 First conditioning potential VY 0 Duration s 0 Equilibration time s 10 AUTOLAB Settings Highest current range 1 0E 2 Lowest current range 1 0E 6 Selected current range 1 0E 3 High sensitivity Off High speed Off High stability On IR compensation Off AUTOLAB GPES A for Windows 0 20m Measurement Number of scans 5 Cell off after measurement On Standby potential V 1 Ferri f Ferro Filename DEMOCV01 Current time 10 34 43 Current date 12 Oct 1998 Potentials Start potential VY 0 398 First vertex potential V 0 6 Second vertex potential V 0 4 Step potential V 0 002441 Scan rate V s 0 099992 Define start potential w r t OCP Off 0 40m 0 30m Cyclic voltammeti 0 10m 0 0 10m 0 20m 0 30m 0 500 0 250 E v0250 2 4 Calculat
156. sentation File can be used to save the adjusted data set 5 4 Baseline correction Four types of baselines can be specified The first is the linear baseline Two markers on the measured curve can be specified which then define a line After acceptation of the markers the corrected curve is also drawn By clicking either the Cancel or the OK button on the Baseline correction window the correction can be either ignored or accepted It is also possible to subtract a polynomial baseline After selecting this option the user is asked to mark between two and five data points as contact points between baseline and curve After accepting the markers the program will calculate a 3rd order polynomial through the markers The third type calculates a connecting exponential curve through the specified begin and end point The whole curve is subsequently corrected for this baseline Finally there is the so called Moving average baseline This is an automatic baseline correction This method is very effective when peaks show as shoulders on steep flanks After a baseline correction real peaks will show The number of data points is reduced by calculating the average within a step window The step window is the minimum peak width which can be specified on the Baseline correction window The baseline is subsequently calculated by comparing each point with the mean value of its two neighbours If the absolute mean value is lower it replaces the current
157. session with the same procedure Save scan as This options allows to save a scan in Cyclic and Linear sweep voltammetry First if more than one scan is recorded a menu is shown from which the user can select the number of the scan to be saved Save data as Similar as the previous option but the name of the file name containing the data can be specified For cyclic and linear sweep voltammetry a submenu is presented from which the required data format can be selected Save data buffer as This option can only be selected for cyclic and linear sweep voltammetry The whole data memory is dumped on disk in binary format in the data directory under a user specified procedure name together with the corresponding procedure parameters This is the only save option which stores all relevant data If a buffer is reloaded all data treatment and save option are open for use 30 User Manual GPES for Windows Version 4 9 Export to scanno vs Q Q file When a cyclic voltammogram is observed with more than one scan it is possible to save the observed cathodic and anodic charge data against the scan number The file with the extension Q amp Q has the following layout ScanNr Q C Q C 1 1 697E 07 2 351E 07 2 1 670E 07 2 365E 07 3 1 671E 07 2 363E 07 4 1 672E 07 2 357E 07 5 1 674E 07 2 356E 07 6 1 675E 07 2 361E 07 7 1 669E 07 2 356E 07 8 1 667E 07 2 358E 07 9 1 674E 07 2 364E 07 10 1 675E 07 2 355E 07 Export Chrono data
158. sis software The routines which perform all the communication with the Autolab instrument Both parts communicate via shared memory The measurement tasks run with the highest priority All the spare time is left for MS Windows applications Familiarisation with GPES is best obtained by experimenting Most of the required help which might be necessary to perform the measurements and the data analysis is provided for by the on line help within the program This manual concentrates more on explaining the general concepts and backgrounds than on guiding the user through the program Moreover this manual tries to explain the possibilities of GPES The Installation and Diagnostics guide explains the hardware aspects the computer requirements and the installation 6 User Manual GPES for Windows Version 4 9 1 2 The concept The design of GPES Windows has been based on the following ideas GPES should incorporate the facilities electrochemists need The user should have full and easy control over the Autolab instrument via the computer How to perform experiments should be easy and clear Actions should require only a few clicks The introduction learning period should be short All important electrochemical techniques should be available GPES should be a full and standard Windows application Series of unattended experiments using different techniques and or procedures should be possible The GPES screen consists of several windows on
159. slow but time consuming measurements a spreadsheet program or word processor is activated The Sleep mode will minimise the time required by GPES During the sleep mode the measuring part of GPES will stay active In this way data are measured but not displayed Chapter 3 The GPES windows 43 Project The Project option allows to execute a large number of electrochemical experiments unattended A project encompasses a number of tasks which have to be executed sequentially Sometimes this is called batch mode processing A measurement procedure is normally activated by clicking the Start button in the lower left corner It 1s also possible to start a procedure by creating and subsequently executing a project A project can be created by selecting the Project edit option First you have to indicate whether a new project should be made New option or an existing project file should be opened Open option An example of a project is delivered with the GPES4 program in the testdata directory After editing a Project it can be stored on disk under its current name Save option or under a new name Save as option When Edit is selected the Edit project window appears with two options on the main menu bar The Check option checks whether there are syntax errors in the project commands The Edit option provides the standard Cut Copy and Paste option Below you will find the Project script language definitions and rules Project command rules Bot
160. ss electrode radius Adjust step size The fit and simulation option for CV automatically searches for the potential step in the CV data However the data can sometimes have an non equidistant step in the potential data i e if measured with ADC750 The fit and simulation software assumes an equidistant step in the potential Therefor the fit can give error messages In order to get rid of these error messages an option to adjust the step to the step potential from the procedure is available The button is visible on the Fit and simulation window when the Extended setup is activated Please note that the kinetic parameters as a result of this fit are not reliable anymore Chapter 4 Analysis of measured data 83 Convergence criteria Fig 52 Convergence criteria Fit and Simulation File Options O Fit Mechanism Reversible El BoA Init guess Fast Fit Simulate Stop Simul Close Adjust step Status Sum simuly 2 Elapsed time s Parameter Value Fity n Convergence not abs Process 1 reduction 1 oxidation 1 Number of exchanged electrons 1 EO v 4608 x 001 Normalized current 4 1 18E 8 x 2 E 3 Background current 4 4 53E 11 x 2 E 3 Start potential v 000 First vertex potential v i Second vertex potential v 000 Number of halfcycles 2 Scan rate s A Step potential W 00045 Value of alpha curr sampling ilk Dimensionless electrode radius le 4 Bulk concentration
161. stigations of factors controlling the transport to the electrode Algorithms for CONVOLUTION srece arai EE E AE E E a iaa dd i 5 11 CONVOLUTION IN PRACTICE 9 12 IR DROP CORRECTION rreren ertean re aE aa Ea aa EE E A E ETEA NAE TEES A direis APPENDIX I GPES DATA FILES esesesseseseeseroroesoesceesoesoresossososeesossesoeoesesossosorossossoeesossososseeosossosse 111 APPENDIX II DEFINITION OF PROCEDURE PARAMETER cscsssssssssessosessessesseseeseeee 113 APPENDIX II COMBINATION OF GPES AND FRA ssccscssssssssscsscssssesscssssessessssessersesssseres 127 APPENDIX IV MULTICHANNEL CONTROL o cccccocconoononconosnonconcononconcononconcononconnonoonosnonconcononcnoss 129 Installanon and a a a a aa a a a aa a a 129 Program operationens tirsir UNT 130 APPENDIX V TECHNICAL SPECIFICATIONS csccsssssssssssscssssscsssssessessssessessssessessssssseseees 133 Interface for mercury electrodes IME 303 and IMEG S oonoonicninnnncinnnnncnnnconnncnnncnnncnnnrnnr rara rra 134 DUO dada die od Ora E odia Hardware specifications of optional modules o s SCAN GEN SCAN250 analog scan generator module ADC750 dual channel fast ADC module ECD low current amplifier module oononnoninnnnonnnnocnnnnnnnnannan nan non cnn annonces BIPOT ARRAY and BA bipotentiostat module ooononninniinninninnjnnnnnnninnnonnccnnrrcnrnnrr narrar FI20 filter and integrator module BSTRIOA or Booster20A current boostet cccescsscescesssesess
162. t bandwidth 1 potentiostat risetime falltime 1 V step 10 90 1 potentiostat modes input impedance of electrometer input bias current 25 C bandwidth of electrometer IR compensation resolution four electrode control front panel meter Analog outputs BNC connector control voltage input multichannel option pAutolab type III 80 mA 12V yes yes 5V 0 2 of setting 2mV 150 uV 300 or 30 uV 10 nA to 10 mA in seven ranges 0 2 of current and 0 2 of current range 0 015 of current range 0 0003 of current range 30 fA 500 kHz lus high speed high stability gt 100 GQ lt 8 pF lt 1lpA gt 4 MHz n a no no potential and current no no Autolab with PGSTAT12 250 mA 12V yes yes 10V 0 2 of setting 2mV 150 uV 300 or 30 uV 10 nA to 100 mA in eight ranges 0 2 of current and 0 2 of current range 0 015 of current range 0 0003 of current range 30 fA 500 kHz lt 500 ns high speed high stability gt 100 GQ lt 8 pF lt 1pA gt 4 MHz depending on selected range 0Q 200Q at 100 mA range to 0Q 200 MQ at 10 nA range current interrupt and positive feedback available 0 025 yes potential and current potential current and optionally charge yes multipleWE option Technical specifications Autolab with PGSTAT302N 2A 30V yes yes 10V 0 2 of setting 2mV 150uV 300 or 30 uV 1
163. t is impossible to determine both the heterogeneous reaction rate k and the formal potential E of the redox couple How to detect dependence of parameters is explained in Finding interdependence of fitted parameters Initial guesses The program provides initial guesses for most of the fitable parameters The exact list of parameters for which initial guesses are calculated is available in the description of the models To calculate initial guesses of the parameters click the button Init guess select option Initial guesses from the Option menu or press Alt I Initial guesses will appear on the screen Also the type of the process reduction or oxidation is set to the default value reduction for scans going toward negative potentials and oxidation for scans going toward positive potentials The type of the process is an extended setup parameter that can be inspected and modified when extended parameter mode is on Ctrl E or the Extended setup option from the Options menu To check the correctness of initial guesses before starting the actual fit switch the mode to simulation option button near the model name and then click the Simulate button A curve will be simulated with the current parameter settings and displayed in Data Presentation window If initial guesses are satisfactory switch back to fit mode and proceed with fitting Special care in checking is required for the number of Exchanged electrons and the Dimensionle
164. t is also possible to load data files from the DOS version GPES3 or data files of other methods or techniques than the current one If this is required click the List Files of Type drop down button and select the proper option You can select multiple files at a time by using lt Shift gt or lt Control gt combined with the mouse action This allows Chapter 3 The GPES windows 29 you to load the work data as well as 10 overlay files After this action it is possible to exchange the work data by clicking Work scan on the Data presentation window Save data Store the most recent measured data under the current procedure name on disk In case of cyclic and linear sweep voltammetry the user is asked to select a scan number first The data are stored in the so called data directory together with the corresponding procedure parameters When more than one scan is recorded in Cyclic voltammetry it is possible to save the previously measured scan while the measurement is going on This option is available at the File menu on the Data presentation window The option is called Quick save of previous scan This option can also be activated by typing SAVE on the keyboard The path and the name of the file can be specified on page two of the Edit procedure window Direct output filename The last five characters of the file name will be used as the scan number Please note These files can be overwritten during another measurement
165. tammogram a selection of the scan to be analysed can be made See Work scan option on the Data presentation window By default the last measured full scan is displayed When a second signal has been recorded concurrent first a selection has to be made which signal should be analysed See Plot menu on the Data presentation window The option is not relevant or cannot activated because an ambiguous situation is present i e it is not clear on what data the analysis should be done 4 1 Peak search When the Peak search option is selected the Peak search window appears If the curve shows distinct peaks you can often simply click the Search button in the right panel and the results are shown in an appearing Results panel The number of digits is the same as the precision of the axis The Clear button will erase the Results window and will refresh the plot The Close button closes the Peak search window The Show results button will show the Results window The Peak search options window gives several options to search for peaks in a voltammogram It opens when the Option button is clicked If Automatic option button is checked the peak search algorithm needs two input parameters to be specified the minimum peak height and the peak width Otherwise only a value for the minimum peak height is required These parameters have to be specified in the Minimum panel Peaks with a height below the minimum peak height will be omitted The peak width para
166. ter Getting started with GPES Positive feedback The Positive feedback option provides an interactive method for determination and compensation of the Ohmic resistance of the cell This option is available only when the Autolab is equipped with a PGSTAT 12 20 30 or 100 potentiostat galvanostat The technique of measurements is based on measuring the current response after applying a potential pulse The current response is displayed on the screen The current response depends on the actual values of the Ohmic resistance and the doublelayer capacitance Compensation of the Ohmic resistance results in a faster decaying of the charging current When the compensation is near 100 the measured current response will show damped oscillation Three parameters need to be specified Potential range Can be either 10 Volt or 1 Volt If the expected measured potential is lt 1 Volt or gt 1 V select the 1 Volt range Otherwise select 10 V range Potential pulse The height of the applied potential pulse A reasonable value is 0 1V Duration The period during which the current versus time data are measured This is twice the duration of the pulse A reasonable value is 0 01 s Chapter 3 The GPES windows 39 When the Start button is clicked current versus time measurements are done repeatedly and the R compensation of the potentiostat is switched on Now the compensated resistance can be varied with the iR compensation slider on the Manual contro
167. ter 4 Analysis of measured data 89 depends on the step height step time and the current sampling parameter a Details regarding the function x at and x bt can be found in literature The electron transfer rates k and k 7 are defined as follows ka k RT nFVD and k k RT nFVD while the Butler Volmer equations for respectively quasi reversible and irreversible processes are I k cp exp onF RT E E c exp 1 anF RT E E quasi reversible I k cp expl onF RT E k c expll onF RT E E irreversible Due to the possible complication of two component voltammograms it can happen that the initial guesses are inferior to those obtained in simpler models However it is always possible to select datapoints by setting the window in such a way that only one peak is covered do initial guesses for one component model and transfer the results to two component model When electron transfer processes are different for example Er Ei all parameters marked with 1 refer to electron transfer Er while all marked with 2 to electron transfer Ei The initial guess procedure can have problems with appropriate assignment of peaks to the components This assignment can be changed by swapping the values referring to the first component and to the second component In case of irreversible electron transfer it is necessary however to adjust the value of a using the relationship Ak anFAE RT loge Normal pulse voltammetry
168. testdata directory 2 From the Edit data menu choose the Smooth option The Smooth window appears and gives you the possibility to choose from different smoothing methods Choose FFT Fast Fourier Transform with linear graph Click the Smooth button the curve is now transformed to the frequency spectrum and a marker window appears You are asked to set one marker for the cut off frequency set this marker at ca 7 Hz and press 20 User Manual GPES for Windows Version 4 9 OK All frequencies above 7 Hz will now be filtered out Please note that the 7 Hz is not the frequency of the potential or current noise The scaling is arbitrary Note the smoothed curve in black with OK you accept the curve and the noisy original will disappear Fig 10 Data smoothing using FFT 10 x File Method Utilities Options Project Window Help eS M 22 gt ME 2 Cyclic voltammetry staircase Normal Procedure DEMOCV04 Data presentation MEE File Copy Plot Analysis Editdata Noisy data from micro electrode 5 micron diameter 1 Check FFT smoothing and wave log analysis 0 175x10 0 150x10 4 0 125x10 4 0 100x10 4 0 075x10 4 Settings JA C Savitzky and Golay smooth Level 0 4 Smooth 0 050x10 4 ee FFT smooth with linear graph 0 025x10 Cancel C FFT smooth with logarithmic graph 04 0 025x10 4 0 050x10 4 T T T T
169. the given fraction of x value Maximum fitting time The time limit of fit procedure If it is set to O default no checking of the time is done Change default value of this parameter only if there is a clear reason to do so Maximum number of iterations The limit for the number of iteration fitting stops earlier if all convergence criteria are satisfied 80 User Manual GPES for Windows Version 4 9 Number of iterations per fitting step Indicates how many iterations are carried out before a signal to break from the user can be processed and the data on the screen is updated Extended parameter setup allows to change default settings of individual convergence criteria for fitted parameters A convergence criterion is satisfied when the change in the parameter value does not exceed the predefined level Convergence criteria may be absolute or relative type of the criterion is indicated by the buttons visible in the extended setup Selecting No button for any parameter disables its convergence criterion numerical value of previous setting remains visible Simulation control parameters Most of the simulation options are set automatically by the program In the choice of their values the program assumes that the parameters of the electrode process have moderate values and tries to find a reasonable compromise between results precision and the calculation time However when extreme values of parameters or extreme combinations of valu
170. the height of the net current in the second to the height of the forward peak Switching between net current and forward backward current will therefore result in the difference in peak heights The potential of the peak is very close to the polarographic halfwave potential Square wave voltammetry quasi reversible electrode process ke Reaction equation REX P Fitable parameters formal potential E V Log normalised electron transfer rate log k transfer coefficient a peak current J A constant background current A Initial guesses available for Ep Ip background current Comments The parameter log k is a 10 base logarithm of the electron transfer rate Ss normalised with respect to the time scale of the experiment k k fDz where fis the frequency and k is the electron transfer rate used in Butler Volmer equation I k cy exp anF RT E E c exp I nF RT E E There is no simple expression for the net peak current The interpretation of the value of Jp depends whether fitting takes place on the net current or on forward backward currents in the first case Ip corresponds to the height of the net current in the second to the height of the forward peak Switching between net current and forward backward current will therefore result in the difference in peak heights Square wave voltammetry irreversible electrode process ne ks Reaction equation R P Fitable parameters 94
171. the limit for the data reduction factor The data set used for fast fitting cannot have fewer points than set by this parameter Maximum number of iterations for Fast Fit The limit for the iteration number After reaching it the fitting procedure switches to regular fit with all data points Fitting in more detail Fast and Full fit When working with larger data sets over 200 points often obtained in cyclic voltammetry it may be attractive to speed up fitting by getting raw values of parameters with a reduced data set and then to refine them using full set For this purpose one can use the reduced data set fitting feature of the fit and simulation program In the reduced data set only every N th point is used in the fitting The number N is called Data reduction factor Certainly this factor cannot be very high because fitting with very few points is likely to deliver parameter values that are not much better than the initial guesses the program can make Therefore the user can define the minimal number of points that the reduced data set must contain The actual reduction factor is the smaller number from the data reduction value set and the total datapoints minimal datapoints ratio Data reduction factor equal to 1 means that no Fast Fit is performed Parameters to control Fast Fit can be set in a window activated by option Fit control parameters from Option menu In the lower part of this window the data reduction factor min
172. the specified value Burette Dose Volume lt Burette number gt lt Dose volume gt dose a specified volume to the specified burette Burette Fill lt Burette number gt Fill the burette Burette Flush lt Burette number gt lt Number of flushes gt flush the burette Burette Reset lt Burette number gt Will give a reset command to the burette Chapter 3 The GPES windows 47 The lt method id gt can be VA voltammetric analysis CV cyclic or linear sweep voltammetry CM one of the chronomethods ECD multi mode electrochemical detection ECN electrochemical noise SAS steps and sweeps PSA potentiometric stripping analysis lt string gt line of text lt filename gt a filename without extension but including a directory name lt scanno gt the number of a recorded scan lt rpm gt rotations per minute The FRA project file can only be executed if the FRA program is already running For more information about the combination of GPES and FRA see Appendix II in the GPES manual A special case occurs when the measurement should start at the open circuit potential Normally the user is asked to click the Continue button but in automatic mode the program continues by itself after 1 second When no scan number is selected in cyclic or linear sweep voltammetry the program uses the last recorded scan as default Examples of projects can be found in the files Demo01 mac and Demo0
173. this error appeared error 20 Negative reactant concentration obtained Negative concentration of the reactant at the electrode surface has been obtained during the simulation of concentration profiles This is usually due to the extreme value of the potential at which the ratio of reactant to product concentration is either very small or very large The general remedy is to shorten the potential range used If 1t is not possible try to use another settings for advanced simulation parameters If this doesn t help please report the problem error 21 Negative product concentration obtained Negative concentration of the product at the electrode surface has been obtained during the simulation of concentration profiles This is usually due to the extreme value of the potential at which the ratio of reactant to product concentration is either very small or very large The general remedy is to shorten the potential range used If 1t is not possible try to use another settings for advanced simulation parameters If this doesn t help please report the problem error 51 GAUSSJ Singular Matrix 1 Two or more parameters in the model are dependent or nearly dependent error 52 GAUSSJ Singular Matrix 2 Two or more parameters in the model are dependent or nearly dependent Descriptions of the models General remarks All models of electrode reactions assume diffusion to an electrode with finite dimensions The size of the electrode is chara
174. tions offers the possibility to measure and compensate for the Ohmic Drop during the measurement This is useful in systems where the Ohmic Drop changes during the experiment At every potential level either a step in staircase cyclic voltammetry or a step in chronoamperometry a small amplitude Dynamic iR amplitude high frequency square wave signal is added By measuring the resulting current responses the Ohmic Drop is calculated Please keep in mind that the following limitations apply to this technique The sweep rate in cyclic voltammetry is limited The method cannot be used in combination with a Rotating Disk Electrode an ARRAY ADC750 BIPOT pX or ECD module or any other device EQCM ESPR etc that will result in an external signal Hardware adjustments are necessary for this option so the option cannot be used on an older instrument with new software only The method only works in High Speed mode Use ECN module ECN Use the ECN module to perform the noise measurements Use high ADC resolution CV staircase fast scan Fast scan measurements are done at a fixed gain If this option is checked the measurement are done at gain 10 of the ADC module otherwise gain 1 is used Use lowest possible interval time CM interval times lt 1s If this option is checked the sample time per level will disappear from the table at page one It is not possible to specify a sample time anymore The sample time is calculated just after the me
175. try ccecccceceesesetececeeceeeensneeeeeeecesennteeeeeeeeeeeaes 29 47 63 126 Load data o aD coat oll been ed alts e lol o 28 31 TE aC SCAN A A RA 28 M MANU ALCON biased shes uote e nN eed eal Mh ett SE eR de 6 37 53 IM arg ard ty ests a A T gat oes 75 Mercury drop lectrode aeisi e a e Ei E EE EEEE E EERE 53 Method O r a a a e E a a e aade 32 Metrohm 730 Sample Changer eeeseeeeeeeessesessresssrrreseretssrsresssreetesresssrreessrersssreessse 49 Index 139 MS Windows res A A a de a ae ed 5 6 MS Wo A A A 6 56 58 64 A sea au E su hae daa T sone abadosebcsidsos bomen ATE 36 MUX Control iaa 36 N NOW o O EAE E cecsosenasvoneteecss E E A E 58 DO EAR E E A E O 40 42 69 97 98 Normal PUSE A A E 113 119 O Open PTOS A A At DA diia 27 E O RN 60 P peak Start ida iia 60 65 67 68 No RO 40 pH electrodes e esa terra o do a lat 39 Platina A tn ade 42 Plot tl ia AA AA 61 polarisation TESIS INC oi sedita EEES T EEEE E ERER E AEE eee 71 72 Positive feedback cri daa dt Ria o EEA E E EER 38 potentiometric stripping analysis ooonoocccnnonccccnonocnnonannnnnnnnnncncnnonnnccnnnnnnanancnncnnns 59 64 POLEO ayi A Ai 5 6 27 38 39 PA ei oee couse a E abc ovve bos ousebe ou cae EEE a EEE dite ERA ERTE TOn 6 28 112 Procedure name in Data presentation WiNdOW ooooccnnnnoccccnonccncnononononancnncnonnnncano nacos 52 Pri A aosa i eade E ERER 43 112 Project cOMMANG TUES sinirini n a e E a aa eiaa 43 NAS AAA eee erei
176. ule ECD the bipotentiostat module BIPOT the 10 A current booster BSTR10A the integrator filter module FI20 for the PGSTAT12 20 30 100 Fig 28 Manual control window Manual control x Current range Settings Potential J iR compensation e FiA 4 gt P 100 mA El O p 4 g O R 10mA 000 y 0 Ohm Ke 1mA O Pe 100uA Integrator O Pe 10uA Current O 001s O h1uA 00 A Potential O01s 7 100nA Co noise Oils 10nd 10s Filter 005 Y Potential o oe Ems O reno 54 User Manual GPES for Windows Version 4 9 It is also possible to perform potential current charge measurements as a function of time Note that some of the Autolab settings are part of the measurement procedure The Manual control window consists of several panels Current range In the Current range panel the green LED indicates the actual current range A mark in the neighbouring check box indicates whether the current range can be selected Only a joined column of selectable current ranges is allowed The software always checks whether the row is closed If a range separated from another range is checked the intermediate ranges are checked automatically When a check box is clicked again the check disappears The allowed current ranges are stored on disk as part of the procedure Sometimes a current range annotation is coloured red This means that 1t is advised not to select
177. us menu options which are frequently used Place the mouse pointer on top of a button Its meaning will appear in yellow if pressing the button is allowed Chapter 3 The GPES windows 53 3 2 Status bar The lowest part of the screen is reserved for the status bar The Start button starts the execution of a measurement procedure After clicking this button other buttons appear which allow to advance to a next stage or to abort a measurement procedure The Status and Message panel give important control information After the Start button is clicked the cell is switched on and the measurement starts with a pre treatment If an automatic mercury drop electrode is connected to Autolab the following control sequence is executed the solution is purged if the purge time exceeds 0 s Subsequently a new drop will be created Then the cell will be switched on and the pre treatment potentials are applied when their duration is not zero During these periods the stirrer will be on Before the measurement starts the stirrer is switched off and the initial or standby potential is applied and the equilibration period starts in order to stop convection of the solution During the pre treatment period the measured dc current is printed in the Manual control window 3 3 Manual control window The Manual control window gives full control over the potentiostat galvanostat of the Autolab instrument including the optional modules the low current mod
178. ut off frequency of for instance 20 means that the amplitudes of the 20 sine waves with the lowest frequencies are kept all other amplitudes are set to zero After a back transformation both the original curve and the smoothed curve are displayed and the question is posed whether the original data should be replaced The FFT algorithm is very effective in removing noise originating from the power source The FFT algorithm is explained in the book Numerical Recipes W H Press et al Cambridge University Press ISBN 0 521 30811 9 FFT smoothing should not be used in data files with spikes or discontinuities It works best 98 User Manual GPES for Windows Version 4 9 if the noise only consists of a periodic disturbance with a higher frequency than the real signal The real signal should not change much within one period of this periodic disturbance Please note that the presented frequency in the frequency domain plot is not the frequency of the noise in the current or potential signal The frequency is presented in an arbitrary unit 5 2 Change all points This option allows to add a constant value to all data points or to multiply all datapoints with a constant value 5 3 Delete points It is possible to remove points from the plot You can specify up to 20 points This option can be used to remove spikes from the measured data With resume Data presentation Plot the original data set will be loaded again The Save work data Data pre
179. value This operation is repeated again and again until no data point is replaced anymore If more than 1000 iterations are required a message is given and the process stops As a default minimum peakwidth a value of 30 mV or less is advised in most cases The process can be hindered by anomalies in the voltammogram Please note that this technique cannot be applied for Cyclic and Linear sweep voltammograms Chapter 5 Editing of measured data 99 Fig 52b Baseline correction window Baseline correction l Settings O Linear baseline Make correction O Polynomial basecurve O Exponential basecurve Moving average Peak width 0 03 Cancel Ok 5 5 Subtract disk file This option allows to subtract a previously measured data set from the current one In case the spacing between the two data sets is different a linear interpolation method is used 5 6 Subtraction of second signal from first signal This option allows to subtract a simultaneously measured second signal using either of the free ADC channels from the current or potential signal first signal In case the spacing between the two data sets is different a linear interpolation method is used The option is only enabled when a second signal is really available 5 7 Derivative First the data points are smoothed according to the Savitsky Golay algorithm see above using smooth factor 2 Subsequently the derivative is determined by th
180. vanostat In order to perform iR compensation the iR compensation button on the Settings panel should be switched to iR comp on Subsequently the Ohmic resistance can be specified using the slider or by typing in the textbox Note that when the iR compensation is switched on automatic current ranging is no longer possible The checked current range box becomes the actual current range In case of a manual change of the current range the compensated resistance will be kept as constant as possible Because internally the compensation is proportional to the current range the value for the compensation needs to be recalculated when the current range is changed With a change of current range the resolution of the compensation will alter The maximum compensation of a current range equals two times the measurement resistance This means that for the 1 A range the maximum 56 User Manual GPES for Windows Version 4 9 compensated resistance is 2 Ohm and for the 1 uA range it is 2 MOhm The resolution is always 0 05 of the measurement resistance Integrator The Integrator panel appears only when the Autolab is equipped with an analog integrator This is not the case with a PGSTAT12 20 30 100 potentiostat galvanostat unless the Autolab is equipped with a FI20 module For further use see the section about chronocoulometry Filter panel The Filter panel appears when the Autolab is equipped with an ECD or an FI20 module The following option butto
181. ve ac voltammetry is applied A convenient value is 0 07 s for differential pulse and differential normal pulse For ac voltammetry 0 5 s is convenient Number of cycles CM interval times lt 1 s The number of times the sequence of potential levels as specified in the potential level table are applied After the measurements only the last cycle is in the computer memory All the measured data of the previous cycles are lost In most cases the number of cycles will be one but for e g pulse plating experiments a higher number can be specified Number of cycles CM interval times gt 1 s The number of cycles you want to measure A cycle includes the pre treatment The old data previous scan will be overwritten by the new one The direct output file when specified is appended with every scan The time parameter also adds up 118 User Manual GPES for Windows Version 4 9 Between two scans the interval time is recorded by the computer clock and this time is also added to the time parameter After reaching the maximum number of points in memory 10000 the on line plot option will stop The actual data points however will be in memory and are plotted after the number of cycles has been reached or after pressing Abort Number of equilibration scans CV Scan averaging Number of cycles of linear sweeps to reach an equilibrium The averaging starts after the specified number of scans The equilibration scans are not kept in
182. veAs c autolab data test channel 4 Example 2 Chrono amperometry on consecutive MUX channels Chapter 3 The GPES windows 49 The following example will perform the c autolab testdata testca procedure on channels 1 to 4 and stores their results using automatic filename numbering The result will be stored as test scanner with cm 001 test scanner with cm 002 test scanner with cm 003 and test scanner with cm 004 with the number corresponding to the channel Procedure Method CM Procedure Open c autolab testdata testca Dataset Autonum 1 Dataset Autoreplace xxx Utility Channel 1 Repeat 4 Procedure Start Dataset SaveAs c autolab data test scanner with cm xxx Utility NextChannel Endrepeat Example 3 Provide or receive trigger signals to or from DIO ports These are the commands to set any of the pins on a DIO port of the Autolab instrument They can for example be used to control a Metrohm 730 Sample Changer Any of the pins can be set from low to high or the other way around and can also be used to receive an input trigger With the SetMode command one specifies whether one wants to send or receive a trigger SetBit allows to set one of the pins to on or off SetByte can be used to set multiple pins to on or off 50 User Manual GPES for Windows Version 4 9 DIO SetMode P1 A OUT On connector Pl port A the mode is set to OUT so ready to send a trigger DI
183. volution As mentioned before there are special algorithms for differintegration as well as for other convolution Below four algorithms used for differintegration and convolution are described in short GO algorithm Gr nwald 0 This algorithm can be used to carry out differintegration to any order The data must be acquired in constant intervals For the order the operation is equivalent to differentiation for 1 to integration using rectangle method For 12 the GO algorithm is the same as semi differentiation For Y2 the GO algorithm is the same as semi integration Error in results increases with the length of the interval and accumulates i e error in latter points is larger than in earlier ones Important advantage is that this algorithm does not require the value of the function for f 0 which makes it very well suited for transformation of chronoamperometric data where i t 0 gt 00 The disadvantage of the algorithm is that the total number of operations is proportional to the square of the number of data points so calculation time grows fast with the length of the data set The fundamentals of this algorithm are described in Oldham KB J Electroanal Chem 121 1981 431 FRLT algorithm Fast Riemann Liouville Transform This is a fast approximate algorithm based on a recursive digital filter It is best suited for differintegration in the range of 0 0 0 5 up to semi integration It is less precise than GO algorithm
184. ward potential step and the second the reverse potential step in a quasi reversible electrode reaction The book of A J Bard and L J Faulkner Electrochemical Methods Fundamentals and Applications Chapter 5 ISBN 0 471 05542 5 gives more details If data for more than two potential steps are present a selection of the first forward potential step can be made This option is only active if it is applicable 4 3 Chronocoulometric plot The Chronocoulometric plot option produces a special plot for two sequential potential steps in a chronocoulometric experiment The first step should be the forward potential step and the second the reverse potential step in a quasi reversible electrode reaction The book of A J Bard and L J Faulkner Electrochemical Methods Fundamentals and Applications Chapter 5 ISBN 0 471 05542 5 gives more details If data for more than two potential steps are present a selection of the first forward potential step can be made This option is only active if it is applicable The charge flown since the beginning of the potential step is plotted versus the square root of the time since the start of the step The kinetic parameters can be obtained by selecting the Linear regression option see below A line should be fitted for the forward as well as for the reverse plot The fit parameters appear in the Analysis results window as well as in the results panel 4 4 Linear regression The Linear regression option
185. ws dots It is sometimes better to draw lines This can be achieved by double clicking the data points in the graph For further information see the paragraph on Editing graphical items Plot The Plot option contains all kind of possibilities to manipulate the graph like plot refresh automatic scaling zooming setting a Data window display of a previously measured signal Sometimes not all options are selectable because they are not applicable or intervene with current active data analysis options Also when the execution of a procedure is going on not all options are selectable New plot The New plot option removes objects such as lines and markers from the screen During measuring a cv this option removes the previous measured data points from the screen Fig 29 The Plot menu GPES Manager Manual control of x File Method Utilities Options Project Window Help AE mJz gt ul 2 418 2 Cyclic voltammetry staircase Normal Procedure AU_SW Data presentation File Copy Mala Analysis Editdata Work scan New plot Automatic F4 Resume Zoom Set window Polycrystalline Auin 0 01M HCIO4 vs SCE y First signal Select overlay scan Load overlay file Reverse axes Enter Text Status Messages Disk file Q 4 858E 05 C Q 4 735E 05 C Manual control Start HA Start Y Exploring c E GPES Mana 1 Edit procedure 4 Manual contro

Table of contents

Contents

Download Pdf Manuals

Related Search

Related Contents