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CV-50W Version 2.3

1. 0 3276 to 3276 Sensitivity 1UA V 100 mA V to 100 nA V Specific Parameters Scan Rate mV sec 20 4 1 to 200 Sample Width msec 17 1 to 250 Pulse Width msec 50 3 to 2000 Pulse Period msec 200 40 to 8000 Drop Time msec 1000 100 to 8000 Quiet Time sec 2 0 0 to 65535 Comments a The Pulse Period is used in NPV the Drop Time in NPP When thedefault parameter value for NPP is different from that for NPV it is shown in parentheses b Increasing the Sample Width can reduce the response noise c The sample interval is equal to the product of the Scan Rate and the Pulse Period or Drop Time e g the default value is 4 mV Graphics Menu Single Graph displays the current vs potential plot 10 22 Analysis Menu The Auto option for Results Graph displays the current vs potential plot and the half wave potential and limiting current are listed in the Main window Alternative baselines can be set by the user through the Manual option Mode DPV P General Parameters Initial E mV 0 3276 to 3276 Final E mV 0 3276 to 3276 Sensitivity 1uA V 100 mA V to 100 nA V Specific Parameters Scan Rate mV sec 20 4 1 to 200 Pulse Amplitude mV 50 250 to 250 Sample Width msec 17 1 to 250 Pulse Width msec 50 3 to 2000 Pulse Period msec 200 40 to 8000 Drop Time msec 1000 100 to 8000 Quiet Time sec 2 0 0 to 65535 Comments a Pulse Period is used for DPV
2. The Auto option for Results Graph displays the current vs potential plot and the peak potentials and peak currents are listed in the Main window for all the segments scanned Alternative baselines can be set by the user through the Manual option Math Menu LSV and CV The derivative voltammogram is sometimes used to measure the peak potential more accurately since the sign of the first derivative change at the peak potential The convoluted voltammograms both semi derivative and semi integral are sometimes reported The semi differential voltammogram has symmetric peaks and better resolution than the standard voltammogram see BAS Capsule 275 and Current Separation article 6 The semi integral is used to correct for iR drop 10 9 10 2 Potential Step Techniques CA CC In these techniques the potential is stepped from one value to another and the current CA or charge CC response is monitored as a function of time it should be remembered that charge is simply the integral of current After the potential has been held at this value for a time 7 the potential can be stepped to another value often the original potential Therefore potential step experiments can be single step or double step The General Parameters are slightly different for CA and CC For CA an initial potential Initial E and high and low potentials High E and Low E are required The potential can be stepped from Initial E to either Low E or High E
3. 0 High E mV 0 Low E mV 0 Scan Rate 100 mV s Initial Direction Negative Number of Segments 2 Sensitivity 1 HA V Specific Parameters Sample Interval mV 1 Quiet Time sec 2 Comments LSV CV 3276 to 3276 3276 to 3276 1 to 51200 100 mA V to 100 nA V 1 to 20 0 to 65535 3276 to 3276 3276 to 3276 3276 to 3276 1 to 51200 mV s Negative or Positive 0 to 65535 100 mA V to 100 nA V 1 to 20 0 to 65535 a The wave form generator that drives the potentiostat is a Digital to Analog Converter DAC with 216 65 636 resolution elements The resolution of the staircase potential wave form is 0 1 mV which generates a potential range of 3276 mV The rate at which the potential can change the Scan Rate is dependent on the rate at which each digital element can be changed This rate is determined by the speed of the clock pulses which is set at 2 048 x 106 10 7 pulses s in the CV 50W The rate of change from the DAC is controlled by allowing only a fraction of the clock pulses to reach the DAC The allowed Scan Rates are calculated from the equation shown below and some values are listed in Table 10 1 If the entered scan rate is between two values the higher scan rate will be used 2 048 x 106 pulses s x 0 1 mV pulse Scan Rate mV s Frequency divisor Frequency divider Scan Rate mV s Frequency divider Scan Rate mV s 4 51200 200 1024 5 40960 201 1019 6 34166 202 1014 7 29257 203
4. po Hz j eb rg Ud Fr 3860 60 He Cell Stand F Purge E Audie aa m CSNDE sia F Keech OME TEsple PreDrops 7 Oukigtion Current Polarty Mims 0 Plus Caneel Fox Figure 3 2 Setup dialog box 3 3 Com Port Baud Rate Line Freq Cell Stand Purge Stir Couple Audible Knock PreDrops This specifies which PC communications port is connected to the potentiostat A value of 0 disables the communication This specifies the rate at which information is transferred between the PC and the potentiostat This specifies the line frequency of the local A C voltage The selected frequency determines the default Sample Width for pulse experiments 17 ms for 60 Hz and 20 ms for 50 Hz 1 line cycle is selected in order to minimize line frequency interference The CV 50W can control the purging and stirring for the BAS Cell Stands and the BAS Controlled Growth Mercury Electrode CGME The knock dispense routines for the SMDE and CGME modes of the Mercury electrode are also controlled by the CV 50W so the Cell Stand option must be set accordingly This activates purging stirring between experiments This couples purging and stirring during the deposition step of stripping experiments This activates a beep before and after each run This synchronizes the drop knock dispense of a mercury electrode with the end of the potential pulse If Knock is not checked then no knock or dispense will occur before o
5. 3 FILE DIALOG BOX ti siii 3 1 IZLOAD DATA counter ns 3 2 ISLISEDATA a A A aA OA AR is 3 2 SASAVE DATA ont deta 3 2 SOLIS TEXT FILE urb ita lata EEEE E 3 2 3 6 CONVERT FILES con pos 3 3 37 DELETE FILES ui ias 3 3 3 9 RENAME FIEES comido dsp 3 3 B20 SEV OP o it 3 3 3 10 TEXT DATA FORMA Tinta 3 5 LEA it ondaa is 3 5 4 METHOD MENU 000 eE Data 4 1 4 1 L0AD SAVE METHOD s tano ch secess E E a EE o EEEE EEEE EEEE E Eh 4 1 42 SELECT MODE coi o EEEE 4 1 4 3 GENERAL SPECIFIC PARAMETERS ea e a e A o i aeae EEE rra oe eTa E EE ENEE 4 2 4A UIST PARAMETERS a a a r a eE a E Saee S oo ERE AREEN ESNE 4 2 4 5 PETER R e NAE a Oy Ria a ee eas 4 3 4 6 DEPOSIT ORTIONS evite 4 3 A STABILIZING CAPACITO Recopila 4 4 4 8 CONTROELED GROWTHA conecta io petits deidades ase 4 4 5 CONTROL MENU Lecuona natin apt banked E A beter 5 1 SH START RUN seco estes Ate ii 5 1 32 HOLD CONTINUE consolida eis ira iio bea iba 5 1 3 3 REVERSE SCAN cut a 5 1 SASTOP RUN A A AA HA aa eas 5 1 33 R N OPTIONS soci iii 5 2 OUISTRUNIDA TA pl lidad 5 3 5 7 TR COMPENSATION veus is ios 5 3 gt e MEASURE REST POTENTIAL 00 iii sis 5 7 59 IMMEDIATE PURGE STIR vio A ME EAA At 5 7 510 CLEAN FLEC TROD E 0 contara Rita 5 8 3 11 SEEP TESTTHARDWARE court ae 5 8 312 EEELON O Econo alias 5 8 6 MATH MENU cuota 6 1 6T OPERATORS nda t 6 1 6 2 SMOOTH ooo aro 6 1 6 3 DERIVATIVE INTEGRAE 00d ita 6 3 64 CONVOLUTION rectora tiroidea E en pE oa dsd nadie dose 6 4 6 3 BACKGROUN Di ld 6 5 A a
6. 8 2 Graph Options This dialog box controls the appearance of the graph on the PC screen and on the hard copy Figure 8 2 All Graph Options are saved in the CVSOW INI file except X Y Freeze and the Min and Max values which typically only apply to a particular data file Asia piliena E de Pere ita P Grid FX imet PY invert TX Freeze Mn E xa P TY Fresca FTE Acie Tithe MY Axia The X Sire Ratio 0 1 fa Y Size Ratio 0 1 pi Cura Options Pam ohyies Lina byte Circ Square CEM Size Bb E Line bebween mnie Trang 7 amori m Phas Carr Exgolor Widhi f itara between aymbola frame width fn El Mufti Graph Side Do a Sete i Te i Toyla Tie Dome Calera Figure 8 2 Graph Options dialog box Axis Options All the axis options can be enabled or disabled by checking the appropriate box Axis When activated both axes are drawn Zero Axes When activated dashed lines are drawn on the graph at X 0 and Y 0 if they are within the range of the graph X Y Grid When activated an X Y grid is displayed X Y Invert When activated the polarity of the X Y axis is inverted X Y Freeze When activated the range of axes is frozen at the selected Min and Max values otherwise the range is adjusted automatically to encompass the 8 2 X Y Titles X Y Size Ratio Curve Options range of the data set Y Freeze but not X Freeze also applies to graphs displayed during experimental runs It is
7. However problems due to circuit instability can arise even when the degree of compensation is significantly less than 100 Therefore the positive feedback is applied in increments of the calculated uncompensated resistance 5 increments up to 80 2 increments from 80 to 90 and 1 increments thereafter The stability of the circuit is tested after each increment The degree of compensation is defined by the user default 100 In the stability test a 50 mV potential step around Test E is again applied and the current data are collected at a rate of 20000 points sec for 50 ms A baseline is measured by collecting data shortly before the potential step is applied and these baseline values are subtracted from the potential step data to yield net current values As the percent compensation increases the current response at first exhibits a ringing effect following exponential decay Figure 5 4 which would eventually go into oscillation The degree of pre oscillation ringing can quantitated by a term defined as Overshoot which the ratio of a minimum net negative current value min to a maximum current value Imax expressed as a percentage that is Overshoot Imin Imax x 100 The maximum allowable Overshoot value is defined by the user Default 10 If the measured Overshoot value is less than 5 5 the maximum allowable value then compensation is continued If it is greater and the desired level of compensation has not y
8. Select Run from the File menu in the Program Manager enter a install or b install in the Command Line Figure 2 4 then click OK Type the nema ole progam der or document ard Windows wil open Ator you Ok Cancel Browne Figure 2 4 Run dialog box 4 The Install dialog box will appear Figure 2 5 Unless specified otherwise the CV 50W software will be installed in the CV50W directory created by the installation routine The CV 50W icon will be installed in the BAS Programs group Click Install CV50W to start the installation 2 9 Ir Wr UA ICON TA Copyright 1996 Biodnalytical Systems Inc All rights reserved Install CVSOW to Drive directori CAcved Figure 2 5 Install dialog box The CV 50W software is opened by double clicking the CV 50W icon Before any operation it is advisable to check that the communication parameters are correct These are contained in the Setup dialog box in the File menu Figure 2 6 Slap Cipriano Comm Port Baud Rate Live Freg p Disabled 13200 50 Hz ri Ca ca Ud C 3600 6D Hz Cell Stand F Purge F Audible FER r SHOE P Stir F Bree r CGME r Couple PreDrops i Oxidation Current Polarity lt Minus Plus Cancel o Figure 2 6 Setup dialog box The Setup communications options are as follows Com Port This specifies which PC communications port is connected to the potentiostat A value of O disables the communication Ba
9. and reloaded using the Analysis File dialog box Clicking Samples produces a dialog box which is used to specify each Sample as either an Unknown or a Standard Figure 7 For each Standard the Concentration and peak potential Ep must been entered for each analyte together with a Tolerance for Ep The Number of Peaks i e the number of analytes being determined must also be specified No information is required for Unknowns Use Prev and Next to move between sample numbers and click Escape to return to the Analysis Calibration dialog box Click Run to start the analysis At the end of each sample run the software will request the next sample When all the samples have been run the calibration curve for a specified peak can be examined by clicking Plot A report that lists the unknown concentration is saved as a REP file the results are also listed in the Main window Process is used for reprocessing of existing files e g if incorrect concentrations or peak potentials were used initially Since 3 digit run numbers are used in the data file names it may be necessary to rename data files before reprocessing It should also be noted that the first run number is now 001 not 0 as in previous versions of the CV 50W software Semple type Llibres E Standard Label Humber of Peaks 1 Conc Epim i Tol Campo Pao 1 fao Feo P Poms Poo d p Peas Y Figure 7 9 Samples dialog box 7 4 Standard Addition This
10. at 54 us and 72 us after the step is applied The current decays exponentially and the initial current l is calculated by extrapolating back to zero time Figure 5 3 Since AE I pRy Ry can be calculated from this measurement To reduce any error this measurement is performed 256 times and the results averaged Re Ru Cal R Figure 5 2 RC circuit used for calculation of the solution resistance 0 54 72 tus Figure 5 3 Exponential decay of current response Ry Q measured RC measured Ry Q error of Ry time constant us measurement 50 3 38 29 42 100 4 94 92 8 4 150 146 145 3 3 200 198 198 1 0 250 250 249 0 4 300 302 301 0 3 347 350 349 0 6 401 406 404 0 7 452 360 449 0 7 Table 5 1 Measured resistance and time constant via exponential extrapolation P He and L R Faulkner Anal Chem 58 1986 523 Table 5 1 shows the results of resistance measurements for various dummy cells using exponential extrapolation There is very good agreement when the time constant is greater than 200 us however the error in the extrapolation is large if the time constant is below 100 us since the current has decayed significantly by the time the response is sampled Therefore the Auto iR Compensation may not work when the uncompensated resistance is low and or the time constant is small Compensation and Circuit Stability Testing Compensation is achieved by positive feedback into the potentiostat
11. command is used to construct a standard addition curve for quantitative analysis First the Mode must be selected and the General and Specific Parameters entered The Standard Addition dialog box appears when Std Addition is clicked Figure 7 10 The Number of Peaks Number of Additions Concentration Unit and Base Filename must all be specified In addition the peak potentials Ep and Tolerances and the total standard concentration after each addition must be entered in the above example there are three standard additions of 10 ppb The Standard Addition parameters and results can be saved using the Standard Addition File dialog box Click Run to start the experiment After each measurement the software will request the next standard addition When all the standard additions have been made the standard addition curve can be examined by clicking Plot A report that lists the unknown concentration is saved as a REP file the results are also listed in the Main window 7 10 Coma 1 Addon 10 Adiong 20 Addiion q 30 adenda Y Addon O Peak 1 Peak 2 Peak J Peak 4 Peak 6 Ep im 35D Tol jarj W Compound Pe Number of Peake 1 Concentration Linit ab Humber of Additiona A Bite Finami AWET comments o oO E Mew ge Losa Bun Process piwe Close Figure 7 10 Standard Addition dialog box Process is used for reprocessing of existing files e g if incorrect standard additions or peak potentials
12. curves Two baselines are required to measure the limiting current These are defined by two points on the I vs E curve 50 mV apart in a range of 250 mV either side of Ey the half wave potential Figure 7 5 Different values are chosen to find the lines of absolute minimum slope APY Aleck Ae HIH Figure 7 5 Sigmoidal current response 7 5 Determination of the Slope and Intercept of an Anson or Cottrell Plot The slope and intercept of the CA Cottrell plot and the CC Anson plot are determined by an unweighted linear least squares fit routine on the last 80 of the data points following both the forward and reverse potential steps Figure 7 6 80 TOTAL NUMBER a OF DATA POINTS 0 FORWARD STEP j E mse 15 8 CHARGE uC o REVERSE STEP sol 80 TOTAL NUMBER OF DATA POINTS Figure 7 6 Selection of points for the Anson plot In all these cases the lines selected by the Auto option are displayed on the screen These can easily be changed using the Manual option The units of calculated slopes are mA ms for Cottrell plot and C ms for Anson plot 7 2 Results Options Pan Shape Ciynmetica Tailing Biguoidal Halt peak width 130 ey iat El Data Geta E Te J i Method a Syrah festar x 1 gt F Aube PF Ind peaks after Loss data Piera Find peaks after Burn Syrenetrical amp tailing reguEe include F Peak Carre F Peak firea
13. diffusion controlled current is given by the Cottrell equation _ nFAD C 1 2 1 2 m t where i current A n number of electrons transferred per molecule F Faraday s constant 96 485 C eq A electrode area cm D diffusion coefficient cm s C concentration mol cm t time s The diffusion controlled faradaic current therefore decays with a typical chronoamperogram is shown in Figure 10 6 The analogous expression for the diffusion controlled charge Qairr is the integral of the above expression 1 e Qairr is proportional to tt anda typical chronocoulogram is shown in Figure 10 7 Although 1 or Q vs t plot is displayed during the experimental run it is also useful to plot i vs t for CA and Q vs t for CC For diffusion controlled systems these are straight line plots and are often referred to as the Cottrell plot for CA and the Anson plot for CC These plots are available as standard plots on the CV 50W 10 11 CA Graph CA1 BIN can min q 3 E z E 3 O Figure 10 7 Chronocoulogram charge time response for double potential step CC Therefore both CA and CC can be used to measure one of n C A and D using the gradients of these straight line plots provided the other three constants are known However other techniques e g pulse techniques have lower detection limits so CA and CC are generally not used for concentration measurements However A and D are frequently
14. every run c Before Auto iR Compensation can be used the iR Test must first be run This test requires three parameters values to be specified by the user Test E this must be a potential at which no Faradaic process occurs Comp Level the degree of compensation default 100 Overshoot the extent of instability allowed in the circuit default 10 d Click iR Test As the test is running the following results are displayed in the Main window Uncompensated resistance R Cell RC constant the product of R and Ca these are the results of the resistance measurements R to be compensated percentage of R used in positive feedback Uncompensated R uncompensated R remaining after compensation these are the results of the stability testing e Ensure that the iR Comp for Next Run check box is activated f Click OK to exit 2 Using Manual iR Compensation a Select the Manual option from Status b Select the appropriate option from Enable c Enter the desired Resistance d Ensure that the iR Comp for Next Run check box is activated e Click OK to exit 5 8 Measure Rest Potential This command measures the open circuit potential This potential is particularly important in studies on corrosion corrosion potential and batteries open circuit potential and it can be used as the initial potential in voltammetry experiments 5 7 5 9 Immediate Purge Stir The Immediate Purge Stir command allows stirring and or
15. for OSWV The potential wave form for OSWV consists of a square wave superimposed on a staircase wave form It can also be viewed as a series of pulses alternating in direction hence the relation to both pulse and A C techniques The current is sampled at the end of each of the pulses or half cycles The default current output is the difference current Figure 10 17 but the forward current if and reverse current ir can also be examined Figure 10 18 For a reversible system the reverse current is significant so the difference current is greater than either the forward or reverse currents This is one reason for the greater sensitivity of OSWV compared with DPV P The magnitude of the reverse current can also be used to investigate the reversibility of the electron transfer 10 25 DSA Graph A rr T y i 4 3 E z E 3 PHAN Figure 10 18 Forward and reverse current responses for OSWV The other advantage of OSWV compared to DPV P is its speed Scan rates of up to 8 V s are available on the CV 50W although scan rates of 100s mV s to a few V s are typically used note that the scan rate for OSWV depends on the square wave frequency This is significantly faster than the scan rate for DPV P ca 10 20 mV s In addition the sensitivity of OSWV compared with DPP V increases with increasing scan rate even for irreversible processes The greater sensitivity and faster speed of OSWV has increased the popularity of t
16. for Smooth is shown below Figure 6 2 6 2 Smoothing Mode e Moving Average e Leat Squares Humber of Points T Fj F Smooth After Run F Replace Current Data Cancel OK smooth Figure 6 2 Smooth dialog box Smoothing Mode Point Smooth After Run Replace Current Data Smooth OK Cancel Default Moving Average This controls the degree of smoothing higher Point produces greater smoothing Default 7 Point When activated the experimental data is automatically smoothed at the end of the experiment Activating this command will transfer the processed data to main memory This command activates selected smoothing routine on the data in main memory This command exits the dialog box whilst retaining any changes This command exits the dialog box without saving any changes 6 3 Derivative Integral These are self explanatory mathematical operations on the current data of the I E curves For differentiation the 1st 2nd and 3rd order derivatives are available Figure 6 3 and are selected using the Order option Additional smoothing is available for the Derivative mode since differentiation can lead to an increase in the noise level Activating the Replace Current Data transfers the processed data to main memory 6 3 Order E 1st Derivative 3nd Derivative ard Derivative Humber of Polite T TRe place Current Data conc Figure 6 3 Derivative dialog box Diffe
17. in CV and LSV limit their usefulness as techniques for quantitative analysis However LSV is used as one of the techniques for the detection of trace metals using stripping voltammetry This is discussed in more detail in section 10 5 It is important to note that the potential wave form used for CV and LSV on the CV 50W and other digital instruments is a staircase wave form since it is impossible to generate digitally a true linear wave form There has been much discussion on the equivalence of digital staircase CV and LSV and analog CV and LSV and it has been shown that variation of the parameters used for the staircase techniques can lead to significant differences Theoretical studies have shown that equivalence can only be guaranteed if the potential step height of the staircase wave form is less than 0 3 n mV where n number of electrons transferred Therefore the potential wave form used on the CV 50W for CV and LSV is identical to a true analog linear wave form since the step height is 0 1 mV BAS has a considerable number CV Notes together with articles and Capsules that describe the applications of CV the articles and capsules are listed below These can be obtained at no charge from BAS BAS Capsules 132 Adsorption of Reduced Glutathione on a Mercury Surface 141 Determination of Heterogeneous Electron Transfer Rate Constant 264 Electrochemical Conversion of Felrs CO 6 to Felrs CO 5 10 5 265 266 267
18. of Runs and the Time Interval between the runs must be specified by the user Note the Time Interval is in addition to the time required to transfer the data to disk The data files are stored automatically after the run in the binary BIN format the Base Filename and the Path drive and directory must be specified by the user The first run starts immediately after OK is selected unless a warning is given that existing files will be overwritten by this operation During each run the title of the graph shows the filename of that run Between runs a small dialog box shows the filenames of the previous and next runs and the time remaining before the next run The filenames of the completed runs are listed in the Main window If the Find peaks after run box is checked Results Options in the Analysis menu a Results Graph and Results List is produced after each run rather than a Single Graph Note that is may require additional time to calculate the results therefore if the Time Interval between runs is critical this option should be unchecked Pressing lt Esc gt at any time during a series of Multiple Runs will abort the present run and any further runs The number of the first run can be specified using Next Run Number This allows a previous set of multiple runs to be continued If a Result file name is entered the program creates a file containing one result line for each run nicely formatted according to the Data Column Se
19. of mass transport In stationary solutions the only mode of mass transport is diffusion whereas in hydrodynamic techniques there is a combination of convection e g stirring and diffusion Therefore in these latter techniques the rate of mass transport can be controlled There is another set of techniques pulse techniques in which the applied potential is a combination of voltammetry and potential step This are discussed in more detail below Sweep Techniques Stationary Solution Cyclic Voltammetry CV Linear Sweep Voltammetry LSV Step Techniques Stationary Solution 10 1 a b c Chronocoulometry CC Chronoamperometry CA Pulse Techniques Stationary Solution Differential Pulse Voltammetry Polarography DPV P Normal Pulse Voltammetry Polarography NPV P Sampled Current Polarography SCP Square Wave Techniques Stationary Solution Osteryoung Square Wave Voltammetry OSWV Stripping Techniques Differential Pulse Stripping Voltammetry DPSV Linear Sweep Stripping Voltammetry LSSV Osteryoung Square Wave Stripping Voltammetry OSWSV Time Base Time Base TB Miscellaneous Bulk Electrolysis with Coulometry BE There are a number of parameters that are common to all techniques Potential range When only a single potential is required this is defined by Initial E If a potential range is required this is defined by Initial E and Final E for single sweep scan step experiments or I
20. printed and hence are invisible In such cases uncheck this option or try different colors This option specifies whether the Results lines e g baselines for peak measurement are to be drawn on the printed graph this option also requires the Print Results text to be active 9 1 Omit file names This option specifies whether the file name is above above graph the graph both on the monitor and on printed copied to clipboard graphs 9 3 Multi Print Files This command sets up a print queue for data files Up to 100 files can be selected from the Multi Print Files dialog box Each data file is printed on a separate page use the Multi Graph option in the Graphics menu followed by Print Graph for multiple graphs on the same page If all the data files are for the same Mode of Operation the Data Sets and Data Type specified in Graph Options are printed If the data files use different Modes of Operation then the default Data Sets and Data Type are used 9 4 Print Text Print Text prints any text selected highlighted by dragging the mouse over the desired lines in the Main window 9 5 Copy Text This command copies to the Clipboard any text selected highlighted by dragging the mouse over the desired lines in the Main window From the Clipboard it can be transferred to other Windows programs 9 6 Copy Graph Copy Graph transfer the present graph window without its frame to the Clipboard From the Clipboard it can be tran
21. the SHIPPED TO destination If the instrument is going to be operated at a voltage other than the standard voltage for the SHIPPED TO area then a change must be made to the input power connector The instructions for changing the voltage requirements are discussed below 110 120 Volts and 60 Hz Operation 110 120V and 60 Hz are the standard power requirements for the Analyzer and its peripheral devices All of these can be plugged into the usual mounted main power outlets 2 1 VOLTAGE SELECT PC FUSE ih ee pa 1 PULL H Figure 2 1 Power connector and voltage select Before plugging the Analyzer power cord into a power socket confirm that the correct voltage has been selected in the power cord connector This is done as follows a Remove the power cord from the power cord connector b Slide the plastic window to the left to expose the voltage select printed circuit card this card is shown in Figure 2 1 The orientation of this card in the connector determines the voltage option c If the number printed on the outer edge of the board does not correspond to the available voltage pull out the card the fuse must be removed first and turn it either by rotation or inversion such that the desired voltage is exposed on the outside edge of the top board Reinsert the board and replace the fuse If the potentiostat
22. the faradaic 10 19 reaction of interest occurs at the diffusion limited rate This technique is useful for discriminating between a reversible redox process rapid electron transfer and an irreversible redox process slow electron transfer on the reverse step since both can be detected by NPV P whereas only the reversible process can be detected by RPV P One example of this is the detection of metal ions reversible in the presence of oxygen irreversible HPP Graph NPP BIN Tipp Gin q 3 E E 3 T si 4 Ponca Figure 10 13 Typical current response for NPV P Differential Pulse Voltammetry Polarography DPV P is different from the previous two techniques in that the current is sampled twice in each Pulse Period The potential wave form is shown in Figure 10 14 The Pulse Amplitude is constant with respect to the base potential and the base potential increases in small steps that is the potential wave form consists of small amplitude pulses superimposed upon a staircase waveform PULSE WIDTH AE ala SAMPLE WIDTH ate AMPLITUD is dl les PULSE PERIOD m Figure 10 14 Potential wave form for DPV P The current is sampled just before the pulse i1 and at the end of the pulse i2 and the difference 12 11 is recorded as a function of the base potential Consider a 10 20 reduction At potentials well positive of the redox potential there is no faradaic reaction is response to the pul
23. this is determined by the Initial Direction Positive or Negative respectively After time qt the Pulse Width the potential can be stepped in the opposite direction from Low E to High E or High E to Low E and is held at this value for time t Figure 10 4 For CC the only potentials are the initial potential Initial E and the final potential Final E Figure 10 5 E PULSE _ _ PULSE __ WIDTH WIDTH HIGH E QUIET TIME INIT E LOWE t Figure 10 4 Potential wave form for CA The current charge response depends on the values of the initial and final potentials If no faradaic reaction occurs at either potential a faradaic reaction is the electrolysis of any molecules in solution then the response is due to charging of the electrode the charging or background current The response is a current spike which decays exponentially 10 10 E PULSE 1 PULSE __ WIDTH WIDTH FINAL E QUIET TIME INIT E t Figure 10 5 Potential wave form for CC Often the initial potential is a potential at which no faradaic reaction occurs and the final potential is a potential at which the Faradaic reaction occurs very rapidly that is the electroactive molecules are electrolyzed as soon as they arrive at the surface of the working electrode The current is therefore determined by the rate of mass transport from the bulk solution to the surface of the working electrode that is the rate of diffusion The
24. 1009 8 25600 204 1004 9 22755 205 999 10 20480 206 994 11 18618 207 989 12 17066 208 984 13 15753 209 980 14 14628 210 975 15 13653 16 12800 i i 17 12047 500 410 18 11378 501 409 19 10799 502 408 20 10240 503 407 21 9752 hs 22 9309 1 mV s resolution Table 10 1 Some allowed Scan Rates for mV s b The Sample Interval potential resolution is dependent on the Scan Rate The best potential resolution for the Scan Rates are shown below Scan Rate v mV s Resolution mV v lt 15753 1 17066 lt v lt 29257 2 34166 lt v lt 40960 3 v 51200 4 CV c The maximum number of data points that can be collected in one experiment is 8000 Therefore a Sample Interval of greater than 1 mV may be required for multisegment experiments Any such changes are made automatically by the software d When the Number of Segments is 0 one complete potential cycle is performed If Initial E is between High E and Low E start at Initial E 10 8 e sweep to one switching potential reverse and sweep to the other switching potential reverse and return to the Initial E If Initial E is the same as either High E or Low E then Number of Segments 0 is the same as Number of Segments 2 The maximum Number of Segments is determined by the data storage capacity and hence depends on the potential range Sample Interval etc Graphics Menu LSV and CV Single Graph displays the current vs potential plot Analysis Menu LSV and CV
25. 271 272 273 274 275 276 Identification of the Products of Oxidation of CpFe CO 2 2 Using Infra red Spectroelectrochemistry Potentiostatic Measurements of a Tc III Tc II Couple Using an OTTLE Cell Cis Trans Isomerization of Ru MeOCS gt PPh3 2 Two Electron Reduction of CpCo NO gt 2 Reductive Dimerization of Cp W NO JL Investigation of Electron Transfer Chain Catalysis Using Cyclic Voltammetry Calculation of the Standard Heterogeneous Charge Transfer Rate Constant ks for Dimeric Iron Fulvalene Complexes Using Cyclic Voltammetry Investigation of E Z Isomerization of Iron Alkenyl Complexes Using Semi Derivative Voltammetry Investigation of the Metal Initiated Oligomerization of Alkynes Current Separation Articles 1 AU 10 11 12 13 14 15 Voltammetry Primer Basic CV R E Shoup 4 1982 31 Cyclic Voltammetry as a Tool for Assessing Dual Electrode Detector Feasibility R E Shoup 4 1982 48 Electrochemistry for the Nonelectrochemist P T Kissinger 6 1985 62 Voltammetric Microelectrodes J O Howell 8 1987 2 Cyclic Voltammetry The Electrochemical Equivalent of Spectroscopy W R Heineman and P T Kissinger 9 1989 15 Doing Things by Halves Semidifferentiation in Voltammetry K Oldham and R Philp 10 1990 3 The Electrochemical Behavior of Nifedipine and Related Compounds and Quantitation of Nifedipine in Plasma by LCEC K Bratin and P T Kissinger 4 1982 4 Reduction of A
26. AA CV 50W Version 2 3 Dh iD January 2001 MF 9093 INSTRUCTION MANUAL Voltammetric Analyzer Bioanalytical www bioanalytical com Systems Inc 2701 Kent Avenue West Lafayette Indiana 47906 MANUFACTURER S NOTE This instrument either wholly or in part is manufactured for research purposes only Use for medical diagnosis is not intended implied or recommended by the manufacturer Use for this purpose and accountability for the same rests entirely with the user The BAS logo is a registered trademark of Bioanalytical Systems Inc MS DOS and Windows are registered trademarks of Microsoft Corporation Other trademarks referenced are the properties of their respective owners 1999 2001 Bioanalytical Systems Inc No portion of this manual may be reproduced without express written permission of Bioanalytical Systems Inc ALL RIGHTS RESERVED Bioanalytical Systems Inc 2701 Kent Avenue West Lafayette IN 47906 USA Phone 765 463 4527 Fax 765 497 1102 bas bioanalytical com www bioanalytical com 1 INTRODUCTION ooo iia 1 1 2 INSTALLATION coo 2 1 2 1 INSTALLATION OF THE CV 50W POTENTIOSTAT cococcccononnnonconnnanconcnnnonnconnonnconnco nono co nonnncncnnnrnss 2 1 2 2 INSTALLATION OF REPLACEMENT ROMS IN THE CV 50W ooocccccccccconnconnonnccnncnnocnncononnncnnnnnnrnns 2 6 2 3 PERSONAL COMPUTER PC INSTALLATION cooooocccconconocnnonnnnnnonnnnnnnonnnnnonnconnonncon non ncon non nonnncnnnnnnrnss 2 8 3 FILE MENU coi A ad oi ia 3 1
27. H ES LL PULSE PERIOD m Ley AE Figure 10 12 Potential wave form for NPV P Consider a reduction If Initial E is well positive of the redox potential the application of small amplitude pulses does not cause any faradaic reaction so there is no faradaic current response When the pulse amplitude is sufficiently large that the pulsed potential is around the redox potential there is a faradaic reaction in response to the pulse assuming moderately rapid electron transfer kinetics and the magnitude of this faradaic current may depend on both the rate of diffusion and the rate of electron transfer When the pulsed potentials are sufficiently negative of the redox potential that the electron transfer occurs rapidly the faradaic current depends only of the rate of diffusion that is a limiting current has been reached This current response is shown in Figure 10 13 The sigmoidal shape is similar to the shape of the curve obtained in the classical polarography experiment which gives rise to the name of normal for this pulse technique The limiting current for NPV P is greater than that for SCP and is therefore a more sensitive technique 30 uA mM and has a lower detection limit 10 M There is a variation of this technique called Reverse Pulse Voltammetry Polarography RPV P In NPV P the initial potential is at a value at which no faradaic reaction occurs whereas in RPV P the initial potential is at a value at which
28. a good idea to run the first experiment with Y Freeze disabled After the data for the first run are regraphed with auto scaling the Min and Max values are correct for the present graph When activated the specified text replaces the default labels on the axes This defines the fraction of the total windows area that is occupied by the graph These control the way the curves are drawn Point Styles Line Styles Data Type Data Sets Six Styles are available in Sizes from 0 to 7 The interior of the Circle Square Diamond and Triangle symbols can be colored by checking Fill Interval between symbols specifies the interval where dots are replaced by symbols for the data points Select Line between points to connect the points with a line of the given Width and select Color to draw the points and lines colored pen This defines how the experimental data is presented when there is more than one presentation format i e BE CA and CC The default Data Types are as follows Current vs Time for CA Charge vs Time for BE This defines which data set is displayed when there is more than one data set i e CV OSWV and OSWSV For CV the number of Data Sets is defined by the Number of Segments specified in General Parameters OSWV and OSWSV The default Data Sets are as follows all segments for CV the first segment for OSWV and OSWSV 8 3 Multi Graph Style The Overlap option draws all curves on the same set
29. accordingly Do not return any products for service until a Return Authorization Number RA has been obtained The RA identifies you as the sender and describes the problem you are having in full detail All correspondence and shipments should be sent to Service Department Bioanalytical Systems Inc 2701 Kent Avenue West Lafayette IN 47906 RAF 2 Installation The installation of the CV 50W Voltammetric Analyzer can be divided into 2 parts installation of the potentiostat and installation of the Personal Computer PC These will be considered in turn 2 1 Installation of the CV 50W Potentiostat Placement As the potentiostat stands in a vertical position it requires little bench space However adequate space should be left near the Analyzer for the PC and any other accessories e g Cell Stands Low Current Module Rotating Disk Electrode In addition the area in front of the Analyzer should not be obstructed as an airflow through the Analyzer is required for cooling Power Requirements The potentiostat can be powered by any of the following A C voltages 100V 120V 220V 240V The A C frequency may be either 50 or 60 Hz The main power source in the location must be the same as the voltage selected in the power cord connector on the rear panel of the potentiostat Figure 2 1 For best results an isolated power line is recommended All potentiostats are configured for the correct voltage and frequency for
30. al problems arise often they are induced into the CV 50W through the environment or power source Ungrounded or fluctuating electrical power sources many also cause abnormal operation Operate your CV 50W from a power source that is free from heavy loads or cycling devices such as refrigerators and ovens A major culprit causing CV 50W malfunction can be the discharge of static into the unit Symptoms include aborting of an experiment in mid run resetting periodically with no operator intervention or an inoperable keyboard Anytime the unit is doing unusual starting stopping drifting into uncalled responses or commands static discharge is most often the problem The solution is to eliminate it or provide a means to dissipate the charge For example placing the unit on a good static mat should reduce this problem This problem is also more prevalent in the winter months when the humidity is low Analog electronic devices tend to drift over time months years and so periodically require recalibration This typically required that the circuit board s be returned to BAS In contrast any problems in the digital circuitry generally leads to catastrophic failure so should be obvious 11 3 Reference Electrodes A poor reference electrode can cause considerable problems so these should be carefully maintained BAS Ag AgCl electrodes are shipped with the Vycor frit covered by yellow plastic This should be removed upon receipt and the electrode
31. ame is shown above this list box and is updated when a different disk drive or directory is selected The path is changed by selecting one of the directories shown in this list and then clicking OK or pressing lt Enter gt alternatively you can double click on the desired directory Files in the selected directory which is now the default directory will then be listed in the Files List Drive Select This drop down list box show the current disk drive To select a different drive click on the Down Arrow box and select the desired drive 3 2 Load Data The Load Data command reloads a data file previously saved by the 100W software in either binary BIN or text TXT CRL SPC and TAB format TXT files from earlier BAS File Service programs can also be loaded 3 3 List Data The List Data command lists the data currently in main memory This allows review of the data without having to save the data as a text file During listing you can press lt Enter gt to Pause the listing or press lt Esc gt to Cancel further lines or click on Pause or Cancel in the CV 50W Listing box 3 4 Save Data Data can be saved in the CV 50W s compact binary BIN format or in the text TXT CRL SPC and TAB format which can be read by other programs 3 5 List Text File The List Text File command is used to list data files previously saved in the text TXT CRL SPC and TAB format Any text file having the TXT CRL SPC an
32. an be performed on either the X or Y data These are addition subtraction multiplication division reciprocal square square root exponent and logarithm Figure 6 1 In addition the slope of the baseline can be adjusted Activating Replace Current Data will transfer the processed data to main memory If this is not activated the processed data can be displayed only once after the math operation has been completed It should be noted that there is a difference in the way the X data is saved for binary and text files In binary files only the initial and final X points and the X sample interval are saved and the remaining X data points are generated when the file is loaded However in text files all the X data are saved Therefore processed X data can only be saved in the text format Mole rates Ligure tet Data Array ox Data Y Data Math Operation Add p r Reciprocal e Subtract Square Reet e Multiply i r Square Divide it Exponential Fr Shope p r Logarithm Replace Current Data E E Figure 6 1 Operators dialog box 6 2 Smooth The digital smoothing routines are used to remove unwanted noise from the electrochemical signal thereby improving the signal to noise ratio and giving more reliable information In all data manipulation programs attempts are made not to bias the signal The major effect of the programs in the CV 50W is the elimination of the 6 1 higher frequency components of the
33. anced by using a working electrode with a large surface area e g platinum gauze reticulated vitreous carbon or a mercury pool and an auxiliary electrode with a large surface area e g platinum coil or gauze in addition the solution is stirred to increase the rate of mass transport to and from the working electrode The auxiliary electrode must be isolated from the working electrode to prevent species that are electrogenerated at the auxiliary electrode from interfering with electrolysis at the working electrode However care must be taken when choosing the material used to isolate the auxiliary electrode from the working electrode since high resistance material may affect the efficiency of the electrolysis Before a BE experiment can be run the potential must be chosen For a reduction the ideal potential is ca 200 mV more negative than the redox potential measured by e g Cyclic Voltammetry so that the rate of electrolysis is controlled by the rate of mass transport to the working electrode However it is not always possible to use a potential too far removed from the redox potential due to electrolysis of other electroactive materials e g electrolyte solvent or other components of the solution mixture When the BE experiment is running a software generated clock on the PC screen indicates the experiment run time At each Sample Interval the current passed during that interval and the total charge passed to that time are dis
34. and Drop Time is used for DPP When the default parameter value for DPP is different from that for DPV it is shown in parentheses b The product of the Pulse Period or Drop Time and Scan Rate must be less than the Pulse Amplitude and greater than 1 mV c When the Pulse Amplitude is negative the direction of the Pulse is opposite to that of the scan d Increasing the Sample Width can reduce the noise e The sample interval is equal to the product of the Scan Rate and the Pulse Period or Drop Time e g the default value is 4 mV Graphics Menu Single Graph displays the current vs potential plot 10 23 Analysis Menu The Auto option for Results Graph displays the current vs potential plot and the peak potential and peak current are listed in the Main window Alternative baselines can be set by the user through the Manual option 10 24 10 4 Square Wave Techniques OSWV Osteryoung Square Wave Voltammetry OSWV is related to both pulse techniques and A C voltammetric techniques It is similar to DPV P in that the current response is a symmetric peak and that there is effective discrimination against background charging currents Its chief advantages are greater sensitivity and faster speed The potential wave for OSWV is shown in Figure 10 16 1 FREQUENCY E la SAMPLE S W AMPLITUD WIDTH f STEP SAMPLE WIDTH I QUIET TIME Figure 10 16 Potential wave form
35. ay be influenced by the rate of heterogeneous electron transfer as well as the rate of diffusion The rate of electron transfer can therefore be measured by CA and CC 5 CC has several advantages over CA The signal increases with time so the latter parts of the response which are least distorted by the finite charging time of the electrode offer better signal to noise ratios in addition any white noise tends to averaged by integration In addition since charge is a summation over the time frame of the experiment the information from the early response is retained However in some instruments this is not strictly the case since the charge is obtained by integrating the discrete current values and some charge is invariably lost In contrast in the CV 50W there is a true charge to voltage converter which means that none of the early information is lost Another application of CC which takes advantage of it s ability to retain early information is the detection of species adsorbed to the surface of the working electrode 3 Such species are electrolyzed very rapidly when the potential is stepped The total charge measured during the CC experiment is Q Qairr Qar Qaas 10 13 Qa is the charge due to charging of the working electrode and Qaas is the charge due to electrolysis of the adsorbed species and is directly proportional to the surface concentration of the adsorbate Of the three components only Qairr is time depend
36. caren Ena peata Figure 7 7 Results Options dialog box Peak Shape This defines the shape of the curve There are instances when the default peak shape selection is not appropriate for example when using microelectrodes at low scan rates as this produces a sigmoidal plot for CV Half Peak Width This defines the expected width of the peak it may be necessary to increase this value for broader peaks Data Type This defines how the experimental data is presented when there is more than one presentation format i e BE CA and CC The default Data Types are as follows Current vs Time for CA and Charge vs Time for BE and CC Data Sets This defines which data set is displayed when there is more than one data set ie CV OSWV OSWSV For CV the number of Data Sets is defined by the Number of Segments specified in General Parameters OSWV and OSWSV have Data Sets 1 to 3 The default Data Sets are as follows all segments for CV the first segment for OSWV and OSWSV Method Sensitivity Factor Find Peaks after Load Data Find Peaks after Run Symmetrical and Tailing Results Included This specifies which option Auto or Manual is to be used This command adjusts the sensitivity of the peak search operation The height of the smallest detectable peak decreases by a factor of 10 for each stepwise decrease in the Sensitivity Factor If this command is activated the Results Graph will be displayed auto
37. d TAB extension can be listed During listing you can press lt Enter gt to Pause the listing or press lt Esc gt to Cancel further lines or click on Pause or Cancel in the CV 50W Listing box 3 2 3 6 Convert Files Convert Files is used to convert data files between the binary BIN and text TXT CRL SPC and TAB formats Up to 100 files can be selected After the file s have been selected the program prompts you to confirm the number of files The text format is determined by the Text Data Format dialog box 3 10 As the converted files are listed on the screen you can press lt Enter gt to Pause the listing or press lt Esc gt to Cancel further lines or click on Pause or Cancel in the CV 50W Listing box Note Files cannot be directly converted from one text format to another text format 3 7 Delete Files Delete Files can delete up to 100 files of any type After the file s have been selected the program prompts you to confirm the number of files As the deleted files are listed on the screen you can press lt Enter gt to Pause the listing or press lt Esc gt to Cancel further lines or click on Pause or Cancel in the CV 50W Listing box 3 8 Rename Files The Rename Files command allows the names of up to 100 files of any type to be changed After the file s have been selected the program prompts you to enter the new file name 3 9 Setup Comm Part Baud Fate Line Freq eg Disabled 18300
38. d screws Item 2 on card rack and slide card retainer plates outward Remove necessary ribbon cables Item 3 by pressing ejectors outward from connectors and remove Remove circuit board by pressing ejectors Item 4 outward and pulling boards straight out NOTE Many of the large scale integrated circuits are static sensitive DO NOT place on plastic e g bubble pack carpeting or other surface which may have static build up To reinstall boards reverse the above procedure
39. e Auto option for Results Graph displays the current vs potential plot s of the Data Sets specified in the Graph and Results Options dialog boxes and the peak potential and peak current are listed in the Main window Alternative baselines can be set by the user through the Manual option 10 27 10 5 Stripping Techniques DPSV LSSV OSWSV Stripping voltammetry is a very sensitive method for analysis of trace amounts of electroactive species in solution Detection limits for metal ions at sub ppb levels have been reported There are 3 important parts in a stripping experiment These are a Deposition b Quiet Time c Stripping These can best be explained by discussing the stripping experiment for detection of lead In this experiment a mercury electrode is used this is either the Hanging Mercury Drop Electrode HMDE or the Thin Mercury Film Electrode TMFE The latter electrode is made by depositing a mercury film on the surface of a glassy carbon electrode This deposition can be done either prior to the stripping experiment or during the deposition step During the deposition step the potential is held at a value Deposition Potential at which the lead ions are reduced to lead metal for a pre determined time period Deposit Time The metallic lead then amalgamates with the mercury electrode when the TMFE is being used mercuric ions are added to the solution and mercury metal is co deposited with the lead during the depositi
40. e cell electrodes Figure 2 2 There are 3 electrode leads and 1 grounded shielding lead The color code is 2 3 Black covered wire Working Electrode lead Red covered wire Auxiliary Electrode lead White covered wire Reference Electrode lead Bare or Black wire w lug Earth ground connector STRAIN A GROUND ON O TO CELL CONNECTO N CV 50W REFERENCE sane AUXILIARY RED WORKING BLACK i P Figure 2 2 Cell electrode end of cell cable A plastic mounting lug near the end of the cell cable provides strain relief by preventing movement of the line or cell Cell Stand Connector This connector is used to control cell stand functions 1 e stirring gas purging and drop knocking and is plugged into the CELL STAND port on the rear panel of the potentiostat There are 3 cell stand configurations available for the CV 50W Analyzer through Setup in the File menu One configuration C2 is for the BAS C2 and C3 Cell Stands and the other two are for the BAS Controlled Growth Mercury Electrode CGME one for the SMDE mode SMDE and one for the CGME mode CGME BAS C2 C3 Cell Stands The purging and stirring functions on the BAS C2 and C3 Cell Stands can be controlled manually or through the CV 50W The REMOTE port on the rear of the Cell Stand is connected via a 23 pin ribbon cable to the CELL STAND port on the rear panel of the potentiostat 2 4 CGME The purge and s
41. e same Mode of Operation the Data Sets and Data Type specified in Graph Options are used to graph the data If the data files use different Modes of Operation then the default Data Sets and Data Type are used File gama Enbalaia E j bm el date Iporl bin a ca Em Zj Se 01 bin 4 dain dppl bin epa bom Hal bis howl hin Lint Haa of hana Ory Binary Dain bin Se dain Figure 8 3 Multi Graph Files dialog box 8 4 9 Print Menu 9 1 Print Graph This command transfers the present graph Single Graph or Multi Graph to the default printer an alternative printer can be selected using Printer Setup using the options specified in Print Options 9 2 Print Options This dialog box contains graph options that pertain only to printed graphs Figure 9 1 F Print srariona tiri F Lhe colore for PrintiGepy grapa F Print Renae pert r Dra An inet F Lobel Fomk flinames abows graphy Figure 9 1 Print Options dialog box Print Conditions text Print Results text Label Use colors when printing Draw Results lines This option lists the experimental conditions This lists the results from the data analysis This is an optional description of the experiment 69 characters maximum This option tells the program that the printer in use knows how to translate colors into ink If it is not checked everything is printed in black or white On black and white printers some colors cannot be
42. ent Therefore the intercept of the Anson plot is Qa Qads One way of calculating Qaas is to measure Qa by performing the CC experiment on the background solution However this assumes that Qa is the same in the presence and absence of the electroactive species this is not necessarily true A more accurate method is to use double step CC since Qa can be eliminated by calculating the difference between the intercepts of the forward and reverse Anson plots Figure 10 9 CE Graph CC1 RIN Figure 10 9 Forward and reverse Anson plots References 1 BAS Capsule No 133 Determination of Electrode Area with Chronocoulometry 2 BAS Capsule No 143 Determination of Diffusion Coefficients Using Chrono coulometry 3 W R Heineman Curr Seps 7 1986 58 67 4 BAS Capsule No 268 Measurement of Reaction Kinetics Using Chronocoulometry 5 A J Bard and L R Faulkner Electrochemical Methods Wiley New York 1980 p 204 206 Mode CA General Parameters Initial E mV 0 3276 to 3276 High E mV 0 3276 to 3276 Low E mV 0 3276 to 3276 Initial Direction Negative Negative or Positive Pulse width msec 250 1 to 32000 Sensitivity 1 uA V 100 mA V to 100 nA V 10 14 Specific parameters Number of Steps 2 1 or2 Quiet Time sec 2 0 to 65535 Graphics Menu Single Graph displays the Current vs Time plot as the default plot The Cottrell plot Current vs 1 sqrt Time can be selected using the Data Type drop down li
43. er is responsible for its safe delivery The following are some guidelines to follow when damage is discovered You should contact the carrier directly for specific claim procedures United Parcel Service UPS Parcel Post Air Parcel Post 1 Retain container packing material and broken item for inspection by the carrier 2 Write or phone BAS with our order number the data received and a description of the damage BAS will do everything possible to expedite repair or replacement of the items damaged Air Freight Express or Truck 1 Contact the local agent of the transportation company immediately and request an inspection 2 Retain the container packing material and damaged goods until the examining agent has made an inspection report In all of the above cases do not return damaged goods to BAS without first contacting our customer service personnel for a Return Authorization Number RAF When a defective part is returned to BAS the RA number immediately identifies you as the sender and describes the item being returned To avoid confusion BAS refuses all unauthorized return shipments Product Warranty Bioanalytical Systems Inc BAS warrants equipment by the company to be free from defects in material and workmanship for a period of 1 year from the date of shipment except as provided hereinafter This assumes normal usage under commonly accepted operating parameters BAS agrees to either repair or replace at its so
44. et been achieved a capacitor is inserted between the reference and auxiliary electrodes to stabilize the circuit and the testing is continued until the desired level of compensation is achieved or the Overshoot value is exceeded if this occurs the amount of compensation to be used in the experiment is slightly decreased from this value One way to increase the level of compensation is to increase the Overshoot percentage It is usually safe to go up to 40 l max l min Figure 5 4 Ringing of the current response If the desired compensation cannot be obtained using Auto iR Compensation then a user specified compensation resistance can be applied using the Manual option If this option is used then a stabilizing capacitor may also need to be selected manually see Stabilizing Capacitor in the Method menu Stabe 7 bute Tae Po me Comp Lyn uo T Osarahost pra 15 Han Gesterornice i ohm Eras or Circe r Ahaya MIR Conpeistion fr Hert Pur Canes or Tes Figure 5 5 iR Compensation dialog box 1 Using Auto iR Compensation a Select the Auto option from Status b Select the appropriate option from Enable If Once is chosen then only the next experiment performed will be iR compensated If Always is 5 6 selected then the amount of compensation determined by the iR Test will be used for every subsequent run Note if Always is chosen the instrument does not redo the iR Test before
45. g boxes for transfer of data files between disk drives and the main memory and for other file manipulation The Load Data File dialog box is shown in Figure List Mes q hepa inary Dima P bir Drier So dota r Figure 3 1 File dialog box File Name File List box List Files of Type This field is used to specify the name of the file which can be either typed or selected from the File List box below Once the file name is shown in the field click OK to activate the selected operation This list box lists all files of the type specified in the List Files of Type field from the sub directory selected in the Directories List field To select a file double click on the file name or click on the file name and then click OK To select two or more data files for commands that accept multiple files drag the mouse over the desired file names or hold down the lt Shift gt key as you select the first and last files in the group If the files are separated hold down the lt Ctrl gt key while selecting Multiple files must be in the same directory CV 50W recognizes its own files by using specific extensions such as BIN TXT or MOD If only one extension type is permitted then that type of file is selected automatically When more than one type of file is allowed 3 1 the program initially selects the previous choice but allows selection of the alternate file types Directories List The current pathn
46. gh as determined by the software to allow time for listing 5 7 1R Compensation In any potentiostatic experiment it is assumed that the potential drop across the interfacial region at the working electrode is the same as the potential applied between the reference and working electrode However this is not true since there is some iR drop between these two electrodes due to solution resistance This resistance can be lowered by addition of supporting electrolyte and in many cases does not need to be considered However there are instances where it is detrimental to the experiment in these cases it can be compensated for electronically On the CV 50W this is achieved by the iR Compensation command There are two stages to Auto iR Compensation on the CV 50W P He and L R Faulkner Anal Chem 58 1986 523 a measurement of the uncompensated resistance b compensation and circuit stability testing 5 3 Measurement of Uncompensated Resistance In this measurement the electrochemical cell is considered to be electronically equivalent to an RC circuit that is the uncompensated resistance Ry is in series with the double layer capacitance Ca Figure 5 2 Since a Faradaic impedance is not considered as part of this model the test potential Test E must be at a value at which no Faradaic process occurs A 50 mV potential step AE is applied around this potential 1 e Test E 25 mV to Test E 25 mV and the current is sampled
47. graph to the end point of the baseline As the mouse is moved within the Results Graph window the coordinates of the mouse cursor are shown in the lower left corner The number of baselines that must be defined depends on the nature of the plot a Symmetric and tail curves define one baseline b Sigmoidal curves define two baselines c Straight line plots define two points on the X axis For symmetric and tailed plots the peak area is also listed in the Main window the peak area is the area between the curve and the user defined baseline Figure 7 1 7 2 BASELINE PEAK POTENTIAL PEAK CURRENT BASELINE PEAK POTENTIAL PEAKAREA Ap PEAK CURRENT El Determination of Peak Potentials and Inflection Points Figure 7 1 Peak area for symmetric and tailed curves NOTE If there are fewer than 30 points available in a data set of segment peak finding is not possible and a warning message is shown The peak potentials of tailed and symmetric current potential curves and inflection points of sigmoidal current potential curves are determined by the manipulation of the first or second derivatives respectively First derivatives are calculated as differentials across a potential window AE of about 25 mV that is Al is calculated as I E 25 mV I E This order is used to produce a consistent sign convention The 25 mV interval is not rigid The actual value is chosen such that an odd number
48. hich the peak is being generated A rapidly changing peak is more likely to be noise rather than a real electrochemical peak This noise discrimination routine is implemented by examining the peak width at 50 100 and 150 mV preceding the peak potential E Figure 7 The peak width ratio AE50 AE100 AESO AE150 and AE100 AE150 are calculated if these are less than the corresponding values for peak with a Half Peak Width of 200 mV Half Peak Width is the difference between the potentials at which the current is half the peak current then the peak is reported E peak A E 50 a E 100 a E 150 Pl 150 100 50 Figure 7 2 Peak finding criteria Determination of Peak Currents Limiting Currents and Peak Areas The most important part of these measurements is the determination of the current baseline The method for this depends on the curve shape Peak area is given in units of Amps x Volts To convert into coulombs for cyclic voltammetry the area must be divided by the scan rate Volts Sec 7 4 a b c Symmetric curves The baseline is the line between the two current minima in the range of Ep 250 mV Figure 7 3 DY Hr DAVI N Figure 7 3 Symmetric current response Tail curves The baseline is the line between two points on the I vs E curve 50 mV apart in a range of 250 mV preceding Ep Figure 7 4 CV Heru CYT AM Figure 7 4 Tailed current response Sigmoidal
49. his technique for quantitative determination of electroactive species in solution The detection limit can be further lowered by using stripping methods which are discussed in section 10 5 Mode OSWV General Parameters Initial E mV 0 3276 to 3276 Final E mV 0 3276 to 3276 Sensitivity 1uA V 100 mA V to 100 nA V 10 26 Specific Parameters Step E mV 4 1 to 40 S W Amplitude mV 25 1 to 250 S W Frequency Hz 15 1 to 200 Sampling Points 256 1 16 256 Quiet Time sec 2 0 to 65535 Comments a b c d e The S W Amplitude must be greater than Step E which is the potential step height for the staircase potential wave form Sampling Points is the number of current samples taken and averaged at the end of each half cycle The 2 current sampling options are i 256 samples taken and averaged over 1 line cycle maximum S W Frequency 15 Hz ii 16 samples taken and averaged over 1 msec maximum S W Frequency 200 Hz The maximum frequency for each option is such that the sampling time is no longer than 1 2 of each half cycle The option is selected by the software The scan rate mV s is the product of the S W Frequency and Step E The sample interval is equal to Step E Maximum data file length is 1279 points Graphics Menu Single Graph displays the current vs potential plot s of the Data Sets specified in the Graph and Results Options dialog boxes Analysis Menu Th
50. ial parameters are required the initial potential Initial E and the two switching potentials i e the potential at which the direction of the scan is reversed High E and Low E The potential wave form for CV is shown in Figure 10 2 The simplest I E curve for CV is shown in Figure 10 3 The asymmetry of the curve is due to the diffusional mass transport However there are many other parameters that can affect the shape of this curve for example slow heterogeneous transfer kinetics instability of the oxidized or reduced species and adsorption If the heterogeneous electron transfer is rapid relative to the timescale of the experiment and both the oxidized and reduced species are stable again on the timescale of the experiment then the redox process is said to be electrochemically reversible The standard redox potential is the mean of the two peak potentials Epa and Epc and the separation of the peak potentials is 57 n mV n number of electrons transferred per molecule 10 3 E HIGHL INITIAL t LOW E E a E SCAN SEGMENTS Figure 10 2 Potential wave form for CV The peak current for a reversible process is given by the Randles Sevcik equation i 2 69x10 n AD Cv where ip peak current A n number of electrons transferred per molecule A electrode surface area cm D diffusion coefficient cm7 s C concentration mol cm v scan rate V s CY Graph CYFR BIN gan
51. initiates the experiment During runs all menus are disabled except the Control commands Start Run Hold Continue Run Reverse Scan and Stop Run After completion of the run the menus are re enabled according to the present mode and data set After a single run the graph is replotted according to the present Graph Options if data are available The Filename label that appears above the graph is cleared to indicate that the data are not yet saved For single runs the data are not saved automatically the Save Data command in the File menu must be used 5 2 Hold Continue Clicking this option or F3 holds the experiment at a given potential The experiment can be restarted by clicking the option again 5 3 Reverse Scan The command or F4 reverses the direction of the potential scan for CV experiments The data for experiments in which this function has been used should be saved as text files binary files will not save the revised potential values correctly 5 4 Stop Run This command or F5 stops the experiment 5 1 5 5 Run Options Heat run number ji TEemite F ut sa0 data Por mingle rung C Enter label before maring deba caei OK _ Bun Humber of Aune ji Bane Filename Path i Time Interval Y 3er Figure 5 1 Run Options dialog box This command allows some automation when running experiments a b It allows repeated experimental runs under the same conditions The Number
52. is operated from a power outlet without a safety ground connection an appropriate adapter must be used The ground connection of this adapter must be securely fastened to an external earth ground for safety and proper operation A proper ground connection cannot be overemphasized The power cord is shipped as a separate item and must be plugged into the connector on the rear panel To insert the power cord into the power socket push up the plastic window and plug in the female end of the power cord The plug type on the male end of the power cord may vary depending on the country of destination The A C frequency is checked for 50 or 60 Hz operation during the Self Test sequence of the potentiostat that occurs on power up see Section 5 11 for more details on this Self Test 2 2 220 240V and 50 Hz Operation 220 240V and 50 Hz are the standard power conditions available in many countries The potentiostat can operate using such power sources To check or change the power requirements of the potentiostat a Remove the power cord from the power cord connector b Slide the plastic window to the left to expose the voltage select printed circuit card this card is shown in Figure 2 1 The orientation of this card in the connector determines the voltage option c If the number printed on the outer edge of the board does not correspond to the available voltage pull out the card the fuse must be removed first and turn it either by
53. is shown in Figure 10 19 OSMASY Graph 3 E E 3 Por iy Figure 10 19 Typical current response for OSWSV It is important to note that it is the concentration of lead in the mercury electrode that is important rather than the concentration of lead in solution The concentration of lead in the mercury electrode can be increased and hence the detection limit of the experiment lowered by increasing the Deposit Time and or the stirring rate The magnitude of these two parameters depends on the sensitivity of the mercury electrode which depends on the surface area to volume ratio 1 e how many of the lead atoms deposited are on the surface and detectable in the stripping step This ratio is considerably higher for the TMFE so a shorter deposition time is required ca 1 2 minutes vs 5 minutes In addition faster stirring can be used with the TMFE due to the relative mechanical instability of the HMDE The signal resolution is also better with the TMFE which can be important when there is more than one metal ion present However the greater sensitivity of the TMFE can also be a disadvantage since the solubility of the metal in the mercury can be exceeded more readily This can lead to the formation of intermetallic compounds which can affect the accuracy of the experimental results e g shifts in the stripping potential and depression of the stripping current One pair of metals that readily combine is zinc and copper In
54. le option and free of part charges to the buyer any parts of such instrumentation which under proper and normal conditions of use prove to be defective within 1 year from the date of shipment Electrochemical cells and working electrodes are warranted for 60 days This warranty and remedy are given expressly and in lieu of all other warranties expressed or implied of merchantibility or fitness for particular purpose and constitutes the only warranty made by BAS BAS neither assumes or authorizes any person to assume for it any other liability in connection with the sale installation service or use of its instrumentation BAS shall have no liability whatsoever for special consequential or punitive damages of any kind from any cause arising out of the sale installation service or use of its instrumentation All products manufactured by BAS are tested and inspected prior to shipment Upon prompt notification by the Buyer BAS will correct any defects in watranteed equipment of its manufacture either by our option by return of the item to our factory or shipment of a repaired or replacement part BAS will not be obliged however to replace or repair any piece of equipment that has been abused improperly installed altered damaged or repaired by others Defects in equipment do not include decomposition wear or damage by chemical action or corrosion Limited obligations covered by this warranty include a In the case of instruments n
55. ltammetry AdSV The basis for CSV is the oxidation of mercury followed by the formation of an insoluble film of HgL L is the analyte on the surface of the mercury electrode during the deposition step This film is then removed in the stripping step using a cathodic scan CSV is most commonly used for the detection of sulfur containing molecules e g thiols thioureas and thioamides but it has also been used for molecule such as riboflavin and nucleic acid bases e g adenine and cytosine AdSV is different from ASV and CSV in that the preconcentration step is non electrolytic and occurs via the adsorption of molecules on the surface of the working electrode the mercury drop is most commonly used The stripping step can be either cathodic or anodic AdSV has been used for organic molecule e g dopamine chlorpromazine erythromycin dibutone ametryne and for metal complexes e g dimethylglyoxime complexes of cobalt and nickel hence AdSV can be used for detection of metal ions that are not suitable for ASV References 1 Stripping Voltammetry A W Bott Curr Seps 12 1993 141 BAS Capsule No 150 Anodic Stripping Voltammetry of Lead and Cadmium 3 An Inexpensive Approach to Inorganic Gunshot Residue Analysis using Anodic Stripping Voltammetry S Chouchoiy and R C Briner Current Separations 4 1982 20 10 30 Deposit Options for DPSV LSSV and OSWSV The Deposit Options dialog box in the Method Menu is used to control
56. matically when a data file is loaded if it is not activated the Single Graph will be displayed If this command is activated the Results Graph will be displayed when the experiment has ended if it is not activated the Single Graph will be displayed Select whether Peak Current and or Peak Area are reported in the results 7 8 7 3 Calibration This command is used to set up a calibration curve for quantitative analysis First the Mode must be selected and the General and Specific Parameters entered The Analysis Calibration dialog box appears when Calibration is clicked Figure 7 8 i Filename F Filename F Filename 1 Filename i Elsrane 3 STD 11 H H di 2 al rr az az ta 33 sw lo as al 44 Er w ul y 15 gt 35 poo x poo qe PA a STD lo 36 36 se lA wl wf wl al a 18 m EL a 3 19 4 da w swa x 40 s Humar of Same fia Dana Fiera pam Concentratian Unk PO Report Mame PWET Comments gt Pb Gems Ml A PA EN E ex oo Figure 7 8 Analysis Calibration dialog box The maximum Number of Samples is 50 A Filename can be specified for each sample if no Filename is specified the Base Filename the sample will be used e g awb11 for sample 1 The Report Name and Concentration Unit must be specified In the above example a total of 10 samples were run 3 of which were standards 1 5 and 10 The Analysis parameters and results can be saved
57. measured using these techniques 1 3 The relationship between i and e or Q and t3 can be used to investigate the period of time for which the current or charge is strictly controlled by diffusion Figure 10 8 shows a plot of i t vs time The deviation from ideality at short times is due to the finite length of time required to charge the working electrode to the step potential The deviations at long times are due to natural convection 10 12 i t TYPICAL DEVIATIONS i we O FP a leak are IDEAL ey oft TIME WINDOW t Figure 10 8 Plot of i t vs t for CA showing time window for condition of planar diffusion Although CA and CC are not used to measure absolute concentrations they can be used to measure changes in concentrations due to homogeneous chemical reactions of the electrolyzed molecules 3 4 This uses the double step technique and measures the ratio of the forward and backward currents or charges If the molecules undergo a chemical reaction after electrolysis in the forward step then these molecules are not available for electrolysis in the reverse step Hence the faster the chemical reaction the smaller the current charge on the reverse step The rate of the chemical reaction can be calculated by measuring the current or charge ratio at different pulse widths If the final potential is at a value at which the electron transfer does not occur rapidly then the current or charge response m
58. ment must be less than or equal to 8000 which is the data storage limit If the product exceeds 8000 then the Run Time is automatically adjusted to an acceptable value c A Precondition potential can be applied for the Precondition Time before the start of the experiment d When enabled the Real Time Integrator adds all the current values to give the charge accumulated Graphics Menu Single Graph displays the current vs time plot Analysis Menu Results Graph is disabled for TB 10 35 10 7 Bulk Electrolysis with Coulometry BE The principle behind the Bulk Electrolysis BE experiment is very simple If only the oxidized species is initially present then the potential is set at a value sufficiently negative to cause rapid reduction and is maintained at this value until only the reduced species is present in solution The total charge passed during the BE experiment Q is related to the number of electrons transferred per molecule n and the number of moles of the oxidized species initially present N through Faraday s law Q nFN where F is Faraday s constant 96500 C mole Therefore if one of n or N is known the other can be calculated Hence BE has both analytical and synthetic applications The cell required for BE is significantly different to that required for voltammetry experiments in which only a very small fraction of the electroactive molecule of interest is electrolyzed The rate of electrolysis is enh
59. mperes 100 milliamperes volt 10 milliamperes volt 1 milliamperes volt 100 microamperes volt 10 microamperes volt 1 microampere volt 100 nanoamperes volt 10 volts Input voltage drift Input current drift Conversion rate Absolute accuracy Resolution Charge to Voltage Converter Maximum charge Range General Input voltage Alternating Current Input power 500 microseconds day maximum 25 picoamperes day maximum 20 000 conversions sec or 50 microseconds conversion 1 fullscale 0 05 fullscale 3 2 millicoulombs 10 microcoulombs volt auto range 1 microcoulombs volt 100 nanocoulombs volt 110 volts 120 volts 220 volts 240 volts 50 or 60 Hertz 720 watts maximum Minimum Personal Computer Requirements Processors Memory Hard drive Floppy drives Ports Mouse Monitor Unpacking and Inspection Carefully unpack the CV 50W from the shipping containers Examine all packing materials before discarding it Inspect all parts for obvious damage Compare 80386 16 MHz 80387 16 MHz 2 MB RAM 80 MB 1 2 MB 5 25 1 44 MB 3 5 2 serial 1 parallel PS 2 14 color VGA items received with the packing documents Damaged Shipments If any damage has occurred whether obvious or concealed all claims must be made to the carrier usually within 15 days of your receiving the shipment otherwise the carrier may not honor the claim Once the item has been assigned to a carrier for shipment the carri
60. n the rear of the system unit The male end of the system unit power cable should be connected to a grounded power strip or outlet It is VERY important to check that the correct voltage has been chosen using the line voltage connector 110 220 V It is also advisable to install a line noise surge protector between the power source and the PC 2 8 e Serial interface connectors COM1 and COM2 These can be used for any serial RS232C device for the CV 50W they are used for communication with the potentiostat and for plotting COM1 is connected with the DATA LINK port on the rear panel of the potentiostat and COM2 is connected with the chosen plotter f Parallel interface connector There is one parallel interface connector LPT1 which is used to connect a parallel printer via a parallel printer cable Setting up the BAS PC is described in more detail in the enclosed User s Guide Once the above connections have been made the system unit and monitor can be powered up Software All BAS PCs are shipped with MS DOS MS Windows and CV 50W Windows software already loaded on the hard disk drive which is labeled as the C drive If a non BAS PC is being used the CV 50W Windows software is loaded according to the following instructions which assume that MS DOS and MS Windows have already been loaded 1 Enter by Windows by typing win at the DOS prompt 2 Insert the CV 50W software disk into the appropriate floppy disk drive 3
61. nitial E High E and Low E for two or more sweep scans steps in the experiment The range for any potential is 3276 to 3276 mV Sensitivity This is the gain of the current to voltage converter output For all techniques except CC the range of sensitivities is 100 mA V to 100 nA V Quiet Time This is the time between the initiation of the Run and the start of the potential scan step The working electrode is connected at Initial E during this time so that equilibration can occur before the start of the experiment The allowed range for the Quiet Time is 0 to 65535 seconds 10 2 10 1 Linear Sweep Techniques LSV CV In LSV the potential is varied linearly from an initial potential Initial E to a final potential Final E at a constant rate Scan Rate and the current is monitored as a function of the applied potential The potential wave form for LSV is shown in Figure 10 1 E FINAL QUIET TIME INIT t Figure 10 1 Potential wave form for LSV A more commonly used variation of LSV is CV In this technique when the final potential is reached the scan direction is reversed and the same potential range is swept again in the opposite direction Therefore the product of the electrochemical reaction on the forward scan can be examined on the reverse scan This feature is one of the main reasons for the widespread use of this technique In CV the potential can be cycled over the same range many times Three potent
62. nnconccononnncnnnoncrnonns 10 28 10 6 TIME BASE TDi ladies 10 34 10 7 BULK ELECTROLYSIS WITH COULOMETRY BE cooconccnocanoconnnocanancnnnonnnonnonnconncnnocnncononnnnnnnnns 10 36 11 SERVICE AND TROUBLESHOOTING 000 eecsseceseeceecneeseeseesesaeeesseceecnesseesesaecaseesecsaeneeaeed 11 1 11 1 PREVENTATIVE MAINTENANCE e e aer a non no a E T ia nn concen neon nro a S 11 1 11 2 TROUBLESHOOTING isseire no e AEE EEEE EET AE EEA E E S 11 1 11 3 REFERENCE ELECTRODES rrean a a E ihe A E aoa ETE snes aens 11 2 11 4 REMOVAL OF CIRCUIT BOARDS ics ccssccssssscesetessssseacsosssensss esses sspsssosthoce tesescsusassbesbsousdaecpssoeteneges 11 5 1 Introduction Sweep Techniques Linear Sweep Voltammetry Cyclic Voltammetry Step Techniques Chronoamperometry Chronocoulometry Pulse Techniques Differential Pulse Voltammetry and Polarography Normal Pulse Voltammetry and Polarography Sampled Current Polarography Square Wave Techniques Osteryoung Square Wave Voltammetry Stripping Techniques Differential Pulse Stripping Voltammetry Linear Sweep Stripping Voltammetry Osteryoung Square Wave Stripping Voltammetry Time Base Amperometric Miscellaneous Bulk Electrolysis with Coulometry Table 1 1 Electrochemical repertoire of the CV 50W Features Fifteen techniques PC control through Windows interface Interaction with other Windows applications Point click user interaction High resolution graphics 100 uV potentiostat resolution Tr
63. ns and segments will allow conversion of bin to a text format without the header and the separators between segments These files cannot be loaded back into the 100W program 3 11 Exit Upon exiting the software the method parameters for the last experiment are saved in a TEMP MOD file and the Setup options Graph Options and Colors window sizes and positions are saved in a SOW INI file 4 Method Menu 4 1 Load Save Method This allows an experimental Method MOD to be Loaded or Saved Method files contain the parameters entered in the Method and Control menus and the Results Options These operations are performed using standard Windows file dialog boxes 4 2 Select Mode There are 15 Techniques available on the CV 50W which are divided into 9 Categories When a given Category is highlighted the modes associated with that Category are displayed in the Technique list box Figure 4 1 The required technique can then be selected After selection the General Parameters dialog box is automatically opened Figure 4 2 Category 1 Sweep Techniques Step Techniques 3 Pulse Techniques Square Wave Techniques Siripaing Techniques Time base Tie Fini ie T Bulk Etectrohyals Teehnlqus CW Cyclic Voltammetry Cy Cyelle Vokfammetny LS Linear Sweep Voltammetry Cancel Ok Figure 4 1 Select Mode dialog box 4 1 4 3 General Specific Parameters Some electrochemical techniques require many different pa
64. nthracyclines at a Glassy Carbon Electrode J Pursley 4 1982 11 Electrochemical Characterization of Ni Ni Fe CN K Kuo 5 1983 30 Electrochemical Characterization of Battery Electrodes K Kuo 5 1983 45 Chromatographic and Electrochemical Investigation of Codeine D A Meinsma and P T Kissinger 6 1985 42 Electrochemical Oxidation of Caffeic Acid Formation of 6 7 Dihydroxycoumarin T M Kenyhercz and P T Kissinger 6 1985 48 Cyclic Voltammetric Studies of Transition Metal Complexes K A Connor and R A Walton 6 1985 67 Transient Electrochemical Response of Thermal Ruthenium Oxide Thin Films in Aqueous Electrolytes E W Tsai P Abraham and K Rajeshwar 9 1990 130 Electrochemistry of C60 and C70 Fullerenes A W Bott 10 1991 137 10 6 16 17 18 19 Cyclic Voltammetry in Organometallic Chemistry A W Bott 10 1991 139 Analysis of the Isomerization of Cr CO n PhPCH CH gt P Ph CH2CH2PPh2 Using Cyclic Voltammetry Simulation A W Bott 13 1994 45 Electron Transfer Induced Isomerization of Cyclooctatetraenecyclo pentadienyl cobalt A W Bott 13 1994 49 Electrochemical Deligation of Bis arene iron I Dications A W Bott 13 1994 70 Mode LSV General Parameters Initial E mV 0 Final E mV 0 Scan rate 100 mV s Sensitivity 1 HA V Specific Parameters Sample Interval mV 1 Quiet Time sec 2 Mode CV General Parameters Initial E mV
65. ocket be careful not to bend the legs of the chips g Properly align new ROM1 on the socket and press in It is imperative that the chip oriented as shown in Figure 2 3 notched end away from the board edge with the ribbon cable connector Be careful not to bend the legs and ensure that all the legs are inserted into the socket h Replace ROMs 2 and 3 in the same way and reinstall board 2 7 2 3 Personal Computer PC Installation Machine Requirements The BAS Windows software was written for use on BAS PCs Other IBM compatible PCs may be able to run this software but there are no guarantees The MINIMUM requirements for the BAS Windows software are a 80386 processor running at 16 MHz together with a math co processor b Hard disk drive c MS DOS version 5 0 or greater d MS Windows 3 1 or greater e VGA monitor f 2 serial interface connectors one for communication with the Electrochemical Analyzer and one for plotting using a serial port plotter g 1 parallel interface connector for a parallel port printer e g laser printer h PS 2 mouse do NOT use a serial mouse PC Connections The important connections are a VGA video display connector b Keyboard connector c PS 2 mouse connector d Power cable connectors for the system unit and the monitor The female ends the two power cables should be connected to these The male end of the monitor power cable should be plugged into the power socket o
66. of axes and the range of the axes is determined by the data in main memory The Tile option displays each data file on its own set of axes 8 3 Graph Colors The colors of each feature on the graph can be selected for both the PC screen and the hard copy These Graph Colors are saved in the CVSOW INI file To change a color first click the colored check box beside the selected feature a cross will replace the color and the sample color patch will change to the present color of that feature Any color can then be mixed by using the Red Green and Blue scroll bars or by typing a number between 0 and 255 in the edit box To apply the present color mix to the selected feature click the checkmarked box once more Note that the accuracy of the colors depends the number of colors the display adapter can depict For Multi Graphs using the Overlap option the Curve 1 through Curve 8 colors are used for the first 8 curves and this sequence repeats for curves 9 through 16 etc Default Colors changes all of the colors back to the original colors 8 4 Multi Graph This plots multiple data files including the data in main memory The Overlap option draws all curves on the same set of axes and the range of the axes is determined by the data in main memory The Tile option displays each data file on its own set of axes Up to 41 files can be displayed and are selected using the Multi Graph Files dialog box Figure 8 3 If all the data files are for th
67. of data points intervene so that the AI value can be assigned to the middle potential of the interval The derivative plots are actually plots of these Al s vs assigned median AE values not AI AE vs AE so the vertical axis has dimensions of current on the same scale used for the AI vs AE plot The derivative values for the first 12 mV and the last 12 mV in a scan are simply equated to the values assigned to the first and last potentials at which AI values could be assigned The second derivative works in the same way but it operates on the first derivative array Peak potentials are determined by examining the first derivative plots The peak potential value Ep is determined by first looking for a sign reversal that is plus to minus or minus to plus The first AI sign reversal becomes the E window note 7 3 that a 25 mV potential window is being examined for each Al calculated To ensure that it is a true peak i e not merely noise two criteria must be met First the 3 points AI values on either side of the Ep window are examined for continuity of sign that is there are three consecutive positive values on the plus side and three consecutive negative values on the minus side If this test is passed the actual E value is determined by choosing the largest current value Imax in a potential window that is 25 mV greater than and less than the median E of the E window The second criterion provides a measure of the rate at w
68. of the Scan Rate and the Pulse Period e g the default value is 4 mV 10 31 Mode LSSV General Parameters Initial E mV 0 Final E mV 0 Scan rate 100 mV s Sensitivity 1 HA V Deposit Time sec 15 Specific Parameters Sample Interval mV 1 Quiet Time sec 10 Mode OSWSV General Parameters Initial E mV 0 Final E mV 0 Sensitivity 1UA V Deposit Time sec 15 Specific Parameters Step E mV 4 S W Amplitude mV 25 S W Frequency Hz 15 Sampling Points 256 Quiet Time sec 10 Comments 3276 to 3276 3276 to 3276 1 to 51200 100 mA V to 100 nA V 1 to 65535 1 to 20 0 to 65535 3276 to 3276 3276 to 3276 100 mA V to 100 nA V 1 to 65535 1 to 40 1 to 250 1 to 200 1 16 256 0 to 65535 a The S W Amplitude must be greater than Step E which is the potential step height for the staircase potential wave form b Sampling Points is the number of current samples taken and averaged at the end of each half cycle The 2 current sampling options are i 256 samples taken and averaged over 1 line cycle maximum S W Frequency 15 Hz ii 16 samples taken and averaged over 1 msec maximum S W Frequency 200 Hz The maximum frequency for each option is such that the sampling time is no longer than 1 2 of each half cycle The option is selected by the software c The scan rate mV s is the product of the S W Frequency and Step E 10 32 d The sam
69. on step The effect of the deposition step is to concentrate the lead in the mercury electrode that is the concentration of lead in the mercury electrode is significantly greater than the concentration of lead in solution this step is often called the preconcentration step The efficiency of the deposition step is increased by stirring the solution or using a Rotating Disk Electrode The time elapsed during the deposition step is shown on the PC screen by a software generated clock During the Quiet Time the stirring is stopped and lead distributes within the mercury electrode to produce a uniform concentration Typically 5 to 10 sec are required for this step During the stripping step the potential is scanned in a positive direction and the lead in the mercury electrode is oxidized back to lead ions in solution at a specific potential that is the lead is stripped from the electrode The stripping potential can be used for qualitative identification of the metal and the stripping current can be used for quantitation of the concentration of metal ions in solution There are a number of different waveforms available for this potential scan Differential Pulse DPSV Linear Sweep LSSV and Osteryoung Square Wave OSWSV Of these 10 28 options DPSV and OSWSV are most often used due to their good sensitivity and low detection limits together with their speed of operation A typical current response for the stripping step for OSWSV
70. or one potential cycle in msec and must be at least twice the Pulse Width Pulse Period is used for voltammetry experiments whereas Dropping Time applies to polarography experiments in which the potential pulse current sampling and renewal of the mercury drop are coordinated this is controlled by the CV 50W As discussed above the current is sampled at the end of the pulse and the mercury drop is knocked off at the end of the Sample Width which coincides with the end of the pulse For polarography experiments using a dropping mercury electrode DME the advantage of sampling the current at the end of the drop lifetime is that the rate of change of the surface area which contributes to the charging current is at a minimum at this point Three different pulse techniques are available on the CV 50W Voltammetric Analyzer These differ in the potential pulse waveforms and the number of sampling times The discrimination against the charging current that is inherent in these techniques leads to lower detection limits compared to linear sweep techniques which make these techniques suitable for quantitative analysis 10 17 Sampled Current Polarography SCP or Tast polarography is a modification of the classical D C polarography experiment and was designed to reduce the effect the changing surface area of the mercury drop The potential wave form is shown in Figure 10 10 The potential is varied in a series of steps it is held at each ste
71. order to be of use as a quantitative analytical technique the results of stripping experiments must be reproducible Therefore experimental conditions must be reproducible Great care must be taken in the sample preparation cleaning of glassware etc The rate of stirring during the deposition step and the condition of the mercury electrode must also remain constant The advantage of using the Rotating Disk Electrode with a TFME is the precise control of the rotation rate however it is easier to obtain a reproducible electrode surface with the HMDE than with the TMFE 10 29 for which careful cleaning and polishing of the glassy carbon electrode surface is required between experiments The above method is called Anodic Stripping Voltammetry ASV since the stripping current is anodic This method can be used for metal ions that can be readily reduced to the metallic state and reoxidized which includes about 20 metal ions e g Pb Cu Zn Cd This is not as many as can be detected using Atomic Absorption Spectroscopy AAS although the sensitivity of ASV is comparable with and sometimes better than AAS The advantage of ASV over AAS is its ability to detect several metal ions simultaneously up to 6 depending on the stripping potentials of the metals present In addition different oxidation states of one particular metal can be detected Other stripping techniques include Cathodic Stripping Voltammetry CSV and Adsorptive Stripping Vo
72. ot of BAS manufacture the original manufacturer s warranty applies b Shipping charges under warranty are covered only in one direction The Buyer is responsible for shipping charges to the factory if return of the part is required c Expendable items including but not limited to carbon paste reference electrodes source lights panel lights and fuses are excluded from this watranty Warranty Card Each BAS analyzer system is shipped with a warranty card which should be completed and returned by the end user This card will enable us to identify and contact the individual responsible for the operation of the instrument Please return the card as soon as possible so that we may inform you of product updates and other pertinent technical information Extended Warranty Agreement BAS offers an extended warranty Full Protection Service Agreement to customers purchasing this system Please contact you Sales Representative or the Service Department at BAS for further details Service Information Bioanalytical Systems provides a skilled staff available to solve you technical and equipment oriented problems For service call 800 845 4246 during normal working hours Eastern Standard Time the year round and ask for Customer Service The operator will route your problem to the correct individual Following discussion of your specific difficulties an appropriate course of action will be described and the problem will be resolved
73. p for the Drop Time and the current is sampled at the end of each drop The Drop Time and the size of the potential step can be varied through variation of the Scan Rate This potential waveform is often referred as a staircase waveform E SAMPLING WIDTH i ae DROP TIME QUIET TIME Figure 10 10 Potential wave form for SCP The current response is shown in Figure 10 11 The limiting current ig is given by the Ilkovic equation SCP Graph SCP AIN popp 4 A E z E 3 Figure 10 11 Typical current response for SCP ia 708nD 2Cm2 7 0 where n number of electrons transferred molecule D diffusion coefficient cm7 s m mercury flow rate mg s t sampling interval s 10 18 The sensitivity and detection limit of SCP are similar to those of DC polarography 5 uA mM and 10 M The major advantage of SCP over D C polarography is the smoothed current output which facilitates measurement of the half wave potentials and limiting currents Although this is a essentially a polarographic technique it can be used as a slow scan rate voltammetry technique This modification is often called staircase voltammetry The potential wave form for Normal Pulse Voltammetry Polarography NPV P is shown in Figure 10 12 and consists of a series of pulses of increasing amplitude with the potential returning to the initial value in between the pulses PULSE WIDTH SE SAMPLE WIDT
74. parator option selected in the Text Data Format dialog box Both multiple and single runs append lines to the result file if it is enabled Comma Space format CSV extension and Tab format files are very easy to import into Excel For convenience of importing all text labels are extracted from the Result file leaving just the data values Note Car Ret Linefeed format works differently than the other formats it saves an exact copy of all lines listed on the screen during each run c The data from single experimental runs can be save automatically by clicking Auto save data for single runs The Path and Base Filename must be specified d Clicking Enter label before saving data allows the user to specify a label for the data file of the experiment just run a dialog box is displayed after each run This can be used for both single and multiple runs However for multiple runs the time available for entering the label is limited by the Time Interval If it is less than 10 seconds this option is not available For longer Time Intervals once the time has expired the data are saved with whatever label has been entered and the next run is then started After a label has been entered and OK has been clicked the standard timer dialog box appears to count down any excess time that remains 5 6 List Run Data When this command is checked in the menu the experimental data are listed on the screen during runs if the data rate is slow enou
75. played on the screen The ratio of the average current during the time interval just passed to that of the first time interval is also shown This ratio is an important criterion for 10 36 determining the extent of the electrolysis that is electrolysis is generally complete when this ratio reaches 1 any residual current being background current This End Current Ratio can be set by the user 1 is the default value In addition to numerical results see below the experimental data can be presented by a charge vs time plot Figure 10 22 or a current vs time plot Figure 10 23 BE Graph REBESUB BIA DEDERUNT u 3 5 E u REGIO HIM Urrea mA L Figure 10 23 Typical current vs time plot for BE The total charge is measured by taking successive readings from the I E converter and adding these values together Although this simplifies the measurement some charge is invariably lost The error depends on the timescale of the BE experiment At very short time less than 0 1 sec the error is typically 1 5 however at 10 seconds the error is only about 0 03 to 0 05 As the timescale of BE experiments is typically of the order of minutes the charge loss due to the simplified measurement technique is generally negligible Another potential source for error in the charge measurement is the use of automatic Sensitivity control since about 3 msec is required for this measurement during 10 37 which time no measu
76. ple interval is equal to Step E Graphics Menu Single Graph displays the current vs potential plot for the stripping step Analysis Menu The Auto option for Results Graph displays the current vs potential plot for the stripping step and the peak potential and peak current are listed in the Main window it should be noted that the default Peak Shape for all the stripping techniques is Symmetric Alternative baselines can be set by the user through the Manual option 10 33 10 6 Time Base TB This is a chronoamperometric technique that is the current is measured as a function of time Generally such techniques are used for amperometric titrations amperometric sensors flow cells etc The simplest potential waveform is obviously a fixed potential and this is the waveform for TB The wave form for TB and a typical current response are shown in Figure 10 20 and Figure 10 21 respectively E INIT OO t E SAMPLE TIME MAX 8000 x SMPL INT q 3 E E 3 Figure 10 21 Typical current response for TB 10 34 Mode TB General Parameters Initial E mV 0 3276 to 3276 Sample Interval msec 500 50 to 20000 Run Time sec 4000 1 to 65535 Sensitivity 1 A V 100 mA V to 100 nA V Specific Parameters Real Time Integrator Off Off On Quiet Time sec 2 0 to 65535 Comments a The Sample Interval is the time resolution of the experiment b The number of data points recorded in an experi
77. purging for a set length of time Purging and stirring can be coupled by checking both boxes in the dialog box Figure 5 6 Immediate Purge Stir dialog box 5 10 Clean Electrode The Clean command is used to hold the electrode at a fixed potential for a set length of time without accumulating any data This can be useful for generating clean reproducible working electrode surfaces Clean E p mi Clean Time P BEG Caneel ar Figure 5 7 Clean Electrode dialog box 5 8 5 11 Self Test Hardware This command initiates the potentiostat electronic self test The results of the test are displayed in the Main window Figure 5 8 E cvs cv an Ele bietod Com Heh nene Gsphcs Erini Hep lt Hon Sep 13 15 04 43 143 tu gt EIDANALYFTICAL SYSTEMS CU Si ROM VERSION 7 4 Moe EMGAGED Ih SELF TEST LIME FREQUENCY ASSURED TO BE 50 HZ ROM 15 OF ARA TS Ok ARALOS SYSTEM IS GF SELF TEST COMPLETE Figure 5 8 Self Test Hardware result 5 12 Cell On Off When Cell On is selected the working electrode is connected at all times When Cell Off is selected the working electrode is only connected during experimental runs For most experiments the cell should be off between runs since there is more chance of damaging the instrument and of personal injury when using the PWR 3 if the cell leads are connected disconnected when the cell is on 5 9 6 Math Menu 6 1 Operators A variety of mathematical operations c
78. r s al bin oc Ibis Opp bim dpl ben isaw bin Hyl les Lisa lis at hypi Binary Dna bah Figure 6 5 Background File dialog box 6 6 Average This command is used to average data files Up to 100 files can be selected from the Average Files dialog box Figure 6 6 see File menu section for a more detailed description of file dialog boxes Fabs gama Evdi Evi hen miiie dam Jeri bin hea bhis how hin Lint Haa of ppa Dia Binary Dain bin e dain bi Figure 6 6 Average Files dialog box 7 Analysis 7 1 Results Graph The data available from an electrochemical experiment may be peak potentials and currents half wave potentials and limiting currents slopes and intercepts of straight line plots or the amount of charge passed during the experiments These data can be obtained using the Results Graph There are two options available Auto and Manual These can be selected from the Results Options dialog box When the Auto option is selected the Results Graph windows displays the experimental data the baseline for peak measurements and the best fit straight line for linear plots the size and position of this windows can be changed by the user by dragging the borders or the caption and are defined initially by the CV50W INI file The Auto option also selects the appropriate Peak Shape The experimental results see below are listed in the Main window CV LSV Selected plot
79. r during the experiment when using the SMDE or CGME modes however if Controlled DME in the Controlled Growth dialog box is checked then the valve is held open but no knock occurs This is the number of mercury drops dispensed from a mercury electrode before the start of an experiment provided the Knock option is checked For SMDE experiments using the BAS CGME the number of Pre Drops depends on the selected drop size as well as the number entered For CGME experiments the number of Pre Drops delivered will match the number entered regardless of the drop size and entering O will allow the same drop to be used for multiple experiments except in polarography experiments 3 4 Oxidation Current This specifies the sign of an oxidation current positive Polarity IUPAC convention or negative classical convention 3 10 Text Data Format When data are listed on the screen or saved in a text format each data point includes an X value typically potential or time and one or more Y values typically current or charge The Text Data Format dialog box provides a selection of data column delimiters Data column separator F CommatSpace txt Space f spe Car Bet Line erly Tab tabj F Omit conditions and segments bio Figure 3 3 Text Data Format dialog box The file extension for each format option is indicated in parentheses The default delimiter is Comma Space and the default extension is txt Omit conditio
80. r pin 4 3 E z E 3 PHEANN Figure 10 3 Typical current response for CV Therefore for a reversible process ip is proportional to the concentration C and the square root of the scan rate v 10 4 As discussed above there are many parameters that can affect the shape of the CV curve Slow electron transfer kinetics can increase the separation of the peak potentials AE and the rate constant for electron transfer can be calculated by examining the variation of AE with scan rate However uncompensated resistance between the working and reference electrodes can also increase AE The effect of uncompensated resistance can be lowered or eliminated using electronic iR compensation see iR Compensation under the Control menu Another application for CV is the study of the reactions of electrolyzed species These are generated on the forward scan and their reactivity can be examined on the reverse and subsequent scans Qualitative estimates of reaction rates can be obtained by varying the scan rates The simplicity and speed of CV means that it is often used as the first technique to characterize a redox system and it is a very powerful technique for qualitative analysis of kinetics and mechanism However quantitative kinetic measurements using CV generally require digital simulation since there is no other way to separate the effects of slow electron transfer and chemical reactivity The charging current that is present
81. r potential is required then the Deposit E option should be selected and the required potential should be entered in the Deposit E field Figure 4 5 Dipea lsa Potential E inital E cpepos E Po Figure 4 5 Deposit Options dialog box 4 3 4 7 Stabilizing Capacitor A stabilizing capacitor is only required when using iR compensation or for Bulk Electrolysis BE experiments In both these cases the Auto option switches a 0 1 uF or 1 uF capacitor into the circuit The Manual option generally only needs to be used when using the Manual iR option Figure 4 6 The Manual option should be used with caution since the addition of capacitors can affect the frequency response of the system Capactor Shabu Ei Auto i uF Manual 23 0 uF Cancel ox Figure 4 6 Stabilizing Capacitor dialog box 4 8 Controlled Growth This specifies drop growth parameters for the CGME mode of the BAS Controlled Growth Mercury Electrode for both pulse and stripping experiments Figure 4 7 The CGME mode must be selected for the Cell Stand options in the Setup dialog box for this item to be activated In the CGME mode the mercury drop is grown using a series of valve openings pulses There are three parameters that defined this series Pulse Width the duration of each pulse Number of Pulses and Delay Time the time between the pulses These parameters are entered under Knock and Dispense Control 4 4 Knock and Dispense Cort
82. r through the Manual option the line is specified by the X values of 2 points on the plot The slope is reported in units of C ms 10 16 10 3 Pulse Techniques SCP NPV P DPV P The basis of all pulse techniques is the difference in the rate of decay of background and faradaic currents following a potential step The background current decays exponentially whereas the faradaic current decays as a function of 1 time that is the rate of decay of the background current is considerably faster than the decay of the faradaic current The background current is negligible at a time of 5RyCq after the potential step RuCa is the time constant for a given electrochemical cell and ranges from us to ms Therefore after this time the measured current consists solely of the faradaic current that is measuring the current at the end of the potential pulse allows discrimination between the faradaic and charging current The important parameters for Pulse techniques are as follow a Pulse Amplitude is the height of the potential pulse in mV b Pulse Width is the duration of the potential pulse in msec c Sample Width is the time in msec at the end of the pulse during which the current is measured It must be at least 2 msec shorter than the Pulse Width The current is sampled and averaged 16 times per msec The default Sample Width is the time required for 1 line cycle d Pulse Period Dropping Time This is the time required f
83. rameters and this can cause confusion For ease of operation the parameters are divided into two categories General and Specific General Parameters must be set by the user for each experiment as there are no standard values for these parameters General parameters always include the potential range Initial E Final E High E and Low E and the Sensitivity the gain of the current to voltage converter Figure 4 2 rene Meyers gi El rie Bo a L Sean Rate ay Pion Hone P e E E 1 Pulses AmpiEudea me Lowe P j Sample Width f Sear Rabe nod lee anes E 1 Inga Direction Euli Width po mane iT hagabora r Postis Pulae Paria pon perio Aumiber of Sages 3 Quiet Time 2 EG genskimy 1 ua El canes ok se Cancel OW Spechic a gt a PEA A Figure 4 3 Specific Parameters Figure 4 2 General Parameters dialog box for DPV dialog box for CV Specific Parameters have default values which have been chosen to be reasonable for most conditions They do not have to be set by the user for each experiment although values other than the default values can be entered Specific Parameters typically include the parameters that define the potential wave form for techniques other than linear sweep potential step and time base for example the Amplitude and Frequency of the square wave potential and the Sample Width Pulse Width and Pulse Period Drop Time for pulse experiments Figure 4 3 4 4 List Parameter
84. rement can be taken This error is only significant if the time constant of the cell is short In these cases it is better to use manual Sensitivity However for most BE experiments the automatic Sensitivity control gives the most accurate results If the manual Sensitivity selection is too low then accuracy is lost but if it is too high overload will occur and the experiment has to be repeated Using a working electrode with a large surface area can lead to oscillation in the electronic circuits To stabilize the system a 0 1 uF capacitor is automatically connected between the reference and auxiliary electrodes The stabilizing capacitance can be increased or removed using the Manual option for Stabilizing Capacitor in the Method Menu However there is generally no need to use the Manual option Mode BE General Parameters Initial E mV 0 3276 to 3276 Sample Interval msec 1000 100 to 65535 End Current Ratio per thousand 10 1 to 1000 Sensitivity Auto Auto 100 mA V to 100 nA V There are no Specific Parameters NOTE Once the End Current Ratio has been reached the experiment should be ended by clicking Stop in the Control Menu or F5 Comment The maximum file length is 4096 data points Graphics Menu Single Graph displays the Charge vs Time plot The Current vs Time plot can be displayed using Data Type in Graphics or Results Options The shape of these plots can indicate chemical reactivity of the electroly
85. rentiation of I is often used for accurate calculation of peak potentials 1st derivative and half wave potentials 2nd derivative 6 4 Convolution In addition to differentiation and integration semi differentiation and semi integration are also commonly used for processing electrochemical data Both of these processes are available on the CV 50W as Convolution Mode options Figure 6 4 Additional smoothing is available for semi differentiation since this process can increase the noise level The convoluted data can transferred to main memory using Replace Current Data Semi differentiation is particularly useful for cyclic voltammetry since it can produce a considerable improvement in the resolution of closely spaced peaks Semi integration can be used to remove the effects of iR drop Conrolutian Made Semi Derivatiwe C Semi ntegral Number of Points r l Replace Current Data canen Figure 6 4 Convolution dialog box 6 4 6 5 Background This command can be used to subtract a voltammogram stored on the hard disk from the voltammogram in the main memory The data file for subtraction is selected from the Background File dialog box Figure 6 5 for a more detailed discussion of file dialog boxes see the File menu section The potential range of the two voltammograms MUST be the same The subtracted data can be transferred to main memory using Replace Current Data Pile pame Polders Cyl bin 1 bb da a Ap
86. rol Pulse Width 100 muta Delay Time 1 mare Humber of Pulses p Controlled DME Drop Control for Deposition r Drop Corina On Pulse Width DE miat Number of Pulses 1 Figure 4 7 Controlled Growth dialog box The CGME can also be used as a DME when in the CGME mode by activating the Controlled DME check box This will open the valve at the start of the experiment and close it at the end of the experiment The mercury will flow freely during the course of the experiment and the Dropping Time i e the time between activations of the drop knocker is selected using Specific Parameters the natural drop time at low potentials in aqueous solution for the standard 150 um capillary is typically slightly less than 1 s The CGME mode can also be used for anodic stripping voltammetry Z Kowalski and J Migdalski Electroanalysis 4 1992 915 The mercury drop is grown incrementally during the deposition step using a series of pulses The drop size is again determined by the Pulse Width and the Number of Pulses which are entered under Drop Control for Deposition The incremental growth in activated by clicking the Drop Control for Deposition check box The Delay Time is determined by the Deposit Time and the Number of Pulses if the Deposit Time is 60 s and the Number of Pulses is 4 then the pulses will occur at the beginning and at 15 30 and 45 s of the Deposit Time 4 5 5 Control Menu 5 1 Start Run This command or F2
87. rotation or inversion such that the desired voltage is exposed on the outside edge of the top board Reinsert the board and replace the fuse If the potentiostat is operated from a power outlet without a safety ground connection an appropriate adapter must be used The ground connection of this adapter must be securely fastened to an external earth ground for safety and proper operation A proper ground connection cannot be overemphasized The power cord is shipped as a separate item and must be plugged into the connector on the rear panel To insert the power cord into the power socket push up the plastic window and plug in the female end of the power cord The plug type on the male end of the power cord may vary depending on the country of destination The A C frequency is checked for 50 or 60 Hz operation during the Self Test sequence of the potentiostat that occurs on power up see Section 5 11 for more details on this Self Test Cell Connection The cell lead cable is the group of wires that connects the Analyzer electronics to the electrodes of the electrochemical cell One end of this cable plugs into CELL on the rear panel of the potentiostat and the other end is attached to the electrodes This may be a direct connection using the general purpose cable sent with the Analyzer or one for attachment to a cell stand such as the BAS C3 Cell Stand The general purpose cell cable terminates with alligator clips that attach directly to th
88. s Defective analog board Poor connections at either end of cell cable Cell lead defective Static discharges Power line disturbances Overheating Poor connections at either end of cell lead Defective cell leads CC discharge relay sticking Corrective Action Plug in Replace fuse Replace cord Replace switch Replace fans Check power supply Call BAS customer service Replace CPU board Call BAS Customer Service Replace I O board Call BAS Customer Service Check connection plug in No cause for undue concern Call BAS Customer Service for advice repair Test power supply DC Make sure all output cables are disconnected before testing Replace analog board Call BAS Customer Service Check cell cable connections Replace cell lead Call BAS Customer Service Install anti static mat Connect to a clean power line Clean filters and check fans don t block cabinet vents Check lead connections Replace cell lead Call BAS Customer Service Replace relay Call BAS Customer Service Bipolarity General Protection Fault Restart CV 50W software CV 50W doesn t respond to PC commands Run Self Test Hardware Linked Failed error message Reset potentiostat or restart CV 50W software 11 4 Removal of Circuit Boards a b c d e PC BOARDS A Analog Board B I O Board C CPU Board Remove white plastic board support item 1 Loosen four designate
89. s The List Parameter command lists the present values of the General and Specific Parameters 4 5 Filter Analog filtering is used during data acquisition to lower the output noise The analog filtering in the CV 50W is a two stage network Figure 4 4 The first stage is an RC filter which is followed by a Bessel filter The filtering characteristics of each stage can be varied and are related to the time scale of the technique being used The capacitor in the RC filter should be chosen to give a time constant RC that is at least 10 times smaller than the time scale of the experiment Similarly the cut off frequency for the Bessel filter must be at least 10 times larger than the frequency of the electrochemical technique being used If too much filtering is used then significant distortion of the experimental data can occur Simus e irha T Mareas Damping Time Constant 3 Jrd Order Fitter Freq 15 3 Figure 4 4 Filter dialog box The amount of filtering used can be determined automatically using the Auto option this 1s the default option It is generally advisable to use this option However the filters can be changed by the user through the Manual option the desired filter is selected fromdrop down list boxes 4 6 Deposit Options Deposit Options is used to define the deposition potential for stripping experiments The default for this parameter is the initial potential for the potential scan Initial E If some othe
90. sdeteseeinsace aks ee seeuyeeuncsetha deen ested EE EEEE EEEE E EE E S a easdereus settee 6 5 Ts ANAT YSIS E E site A eee ne ace ened taeda 7 1 T ERESULIS GRAP Ociosos 7 1 1 2 RESULTS OPTION So e Ae A ees 7 7 TI CALIBRATION te seteets teen tadas diia 7 9 TA STANDARDA p ON c 0 ocio titi illes ita dee ico dass 7 10 3 GRAPHICS MENU ot 8 1 SUL SINGLE GRAP Host ei ASA seb endebe NEEE AEE AE 8 1 8 2 GRAPH OPTIONS cintia i 8 1 8 3 GRAPH COLORS porat eoe ia TT EE E E aE AE E E SE EES E 8 3 8 4 MULTEGRAPH tice fii tio el eee rd iio Seneca RS AEA toes 8 4 o PRINT MENU joie e st i el titan ath 9 1 9 1 PRINT GRAPH cessor fc soccses Ad dovcten dpi in ride dk tease 9 1 9 2 PRINT OPTIONS utopia se he eB ostia 9 1 9I3SMULTERRINTEILES ciar td iia 9 2 SAPRINTIE Toro lielaprir ss 9 2 DS CORN TEX Titi ibi 9 2 9 6 COPY GRAPHY eis ie seghn Beitects Reales BE rara 9 2 9 7 PRINT SETUP it ii ie SAS 9 2 10 OPERATION MODES uc paisa 10 1 10 1 LINEAR SWEEP TECHNIQUES LSV CV eeren cecsesecsecnseesecesceseeseceeesseseaeeseecaecnaecaessaseasensensees 10 3 10 2 POTENTIAL STEP TECHNIQUES CA COecconconocconoconconccnncnnonanonnnnnncancnnnonncon non nn cnn cn erie Serek soste 10 10 10 3 PULSE TECHNIQUES SCP NPV P DPV P reie sro sei eneee ieri 10 17 10 4 SQUARE WAVE TECHNIQUES OSWV oocoocccccccococonoonocnccnnconocnnonnonnncnncnanonnnonncnncon non no cnn co nenncann cons 10 25 10 5 STRIPPING TECHNIQUES DPSV LSSV OS WS V eooococccconacococnnocnnanccnnonaconno
91. se so the differential current is zero At potentials around the redox potential the differential current reaches a maximum and decreases to zero as the current becomes diffusion controlled The current response is therefore a symmetric peak Figure 10 15 DPP Graph PP JBN appi Gin 4 3 E 7 E 3 T Ponca Figure 10 15 Typical current response for DPV P The sensitivity of DPV P is intermediate between NPV P and SCP 20 uA mM but the detection limit of DPV P is significantly lower 10 M due to more effective discrimination against the charging current Mode SCP General Parameters Initial E mV 0 3276 to 3276 Final E mV 0 3276 to 3276 Sensitivity 1uA V 100 mA V to 100 nA V Specific Parameters Scan Rate mV s 4 1 to 200 Sample Width msec 17 1 to 250 Drop Time msec 1000 100 to 8000 Quiet Time sec 2 0 to 65535 Comments a Increasing the Sample Width can reduce noise b The step height or sampling interval is the product of the Scan Rate and the Dropping Time e g the default values is 4 mV Graphics Menu 10 21 Single Graph displays the current vs potential plot Analysis Menu The Auto option for Results Graph displays the current vs potential plot and the half wave potential and limiting current are listed in the Main window Alternative baselines can be set by the user through the Manual option Mode NPV P General Parameters Initial E mV 0 3276 to 3276 Final E mV
92. sferred to other Windows programs 9 7 Print Setup This command allows the default printer and other printer options to be changed without using the Control Panel The options available depend on the type of printer and the printer driver installed in Windows 9 2 a b 10 Operation Modes There are 15 techniques available on the CV 50W This may appear to be a bewildering number but many of these techniques are related or are variations of other techniques There are a number of broad divisions that can be made Control Potential Voltammetry Chronoamperometry I vs E I vs t at fixed E Pulse Voltammetry Hydrodynamic DPV SWV NPV SCP Hydrodynamic RDE HDM Stationary Solin Stationary Soln Control Potential Electrolysis Small Amp Large Amp ACV PSACV SHACV CV LSV CA LC EC CC Voltammetry vs chronoamperometry potential step In voltammetry the potential is varied in a defined manner and the current response is monitored In chronoamperometry the potential is held at a fixed value or is stepped between two values and the current response is monitored as a function of time Stationary solution vs Hydrodynamic This determines the rate at which electroactive molecules are brought to the surface of the working electrode 1 e the rate
93. should be stored with the Vycor frit immersed in a solution of 3M NaCl where it should remain when not in use Other reference electrodes should also be stored in the appropriate solution e g saturated KCI for the saturated calomel electrode Failure to store reference electrodes properly can lead not only to a drift in the electrode potential but it can also causes precipitation of salts in the frit This can in turn result in very noisy data Similar effects can also be caused by presence of air bubbles next to the Vycor frit These can be removed by gently flicking the end of the electrode Symptom When CV 50W is turned on fans do not run Self Test Diagnostic Failures Any ROM error error in RAM 1 3 4 6 or BANK SWITCH ERROR Error in RAM 5 Self Test reads RAM OK ROM OK and doesn t continue on to analog test Error in or 2 analog tests Error in several analog ranges Operation appears to be normal but no data is acquired Random malfunctions The following Analog errors simultaneously Error in ranges 5 4 3 Possible Cause Not plugged in Blown fuse Defective power cord Defective power switch Defective fans Defective power supply Defective CPU board Defective I O board 40 pin jumper between analog and I O boards not making contact Small offset is present in analog system This may be caused by temperature changes or long term calibration drift Power supply voltages out of tolerance
94. signal typically 10 s of Hz and greater the exact cutoff frequency depends on both the electrochemical and smoothing techniques There are 2 methods for digital smoothing These are a a modified variable point linear smoothing routine Moving Average b a variable point least squares smoothing routine Least Square Moving Average In the modified 5 point linear smooth data is examined in 5 point blocks Within each block the first second fourth and fifth points are summed and divided by 4 This number an averaged current value replaces the third point in the block The averaging routine moves up 1 point and repeats the averaging sequence This routine is repeated for all points The first 2 points of the data set are set equal to point 3 and the last 2 points of the data set are set equal to the third from last point At times this appears as spurious data points at the ends of the plot This is unavoidable and is normal The only requirement for the number of points is a block is that this number is odd Any odd number between 5 and 25 can be chosen on the CV 50W the larger the number of points the greater the smoothing Least Squares This digital smoothing function is based on the work of Savitzky and Golay A Savitzky and M J E Golay Anal Chem 36 1964 1627 1639 The smoothing 1s a quadratic least squares operation working on data blocks of n points where n is any odd number between 5 and 25 The dialog box
95. st box in the Graphics Options dialog box Analysis Menu The Auto option for Results Graph displays the plot selected in Data Type and the slope intercept and correlation coefficient are listed in the Main window Since data at early time points can be distorted due to the finite time required for the potential step the Auto option uses only the last 80 of the data An alternative line can be defined by the user through the Manual option the line is specified by the X values of 2 points on the plot The units for the slope are mA ms Comment The maximum data file length is 1000 pts step Mode CC General Parameters Initial E mV 0 3276 to 3276 Final E mV 0 3276 to 3276 Pulse Width msec 250 3 to 32000 Sensitivity 1 uC V 100 nC V to 10 uC V Specific Parameters Number of Steps 2 1 or 2 Quiet Time sec 2 0 to 65535 Comments The maximum file length is 1000 points step The circuitry for CC is a direct charge to voltage converter The integrating capacitor that is used to accumulate the charge in the 10 uC V Sensitivity range is automatically discharged and reset to zero when it nears the voltage saturation level This operation allows a much greater charge to be measured during the experiment Discharging the capacitor requires 0 5 msec during which time no charge is measured We have never had a situation where this has caused a noticeable error in the output since discharge typically occursafter the ini
96. tailed curve Experimental results peak potential current and area DPV P OSWV Selected plot symmetric curve Experimental results peak potential current and area DPSV LSSV OSWSV Selected plot symmetric curve Experimental results peak potential current and area NPV P SCP Selected plot sigmoidal curve Experimental results half wave potential CA CC Selected plot straight line plots i vs t 1 2 for CA Q vs t 2 for CC Experimental results slope and intercept N B Due to the finite time required for the potential step to be complete the data in the first few milliseconds of potential step experiments is often distorted 7 1 The CV 50W Auto option therefore only uses the last 80 of the collected data when calculating slopes and intercepts BE Experimental results Initial current End current Current ratio Time Total charge Net charge In addition to the Results Graph the Results Graph window also displays the coordinates of the mouse cursor as it is moved within the axes A selected area can be expanded Zoomed by dragging the mouse using the left mouse button between diagonally opposite corners of the defining rectangle This operation can be reversed by clicking the left mouse button When using the Manual option the baselines for calculation of results are defined by the user Click and hold down the right mouse button at the starting point of the baseline and drag the mouse across the
97. the Deposition Potential The default for this parameter is the initial potential for the potential scan Initial E However if some other potential is required for the Deposition Potential then the Deposit E option should be selected The desired Deposit E can then be entered The electrode potential is always held at Initial E during the Quiet Time Mode DPSV General Parameters Initial E mV 0 3276 to 3276 Final E mV 0 3276 to 3276 Sensitivity 1uA V 100 mA V to 100 nA V Deposit Time sec 15 1 to 65535 Specific Parameters Scan Rate mV sec 20 4 1 to 200 Pulse Amplitude mV 50 250 to 250 Sample Width msec 17 1 to 250 Pulse Width msec 50 3 to 2000 Pulse Period msec 200 40 to 8000 Quiet Time sec 10 0 to 65535 Comments a b c d e Sample Width is the time at the end of the pulse during which the current is measured The default value is the time required for 1 cycle Increasing the Sample Width can decrease the noise level Pulse Width is the duration of the pulse and must be at least 2 msec longer than the Sample Width Pulse Period is the time required for 1 potential cycle and must be at least twice the Pulse Width The product of the Pulse Period and Scan Rate must be less than the Pulse Amplitude and greater than 1 mV When the Pulse Amplitude is negative the direction of the Pulse is opposite to that of the scan The sample interval is equal to the product
98. tial large current transients have decayed and the current isrelatively small so the charge lost over 0 5 msec is less than the 10 15 resolution of the instrument and the expected precision of the experiment However errors can occur if the initial current are very large since this may cause discharging at short times Such errors are shown by discontinuities in the Charge vs Time plot If this occurs the initial current must be decreased by for example decreasing the concentration and or the electrode surface area The automatic discharge is not allowed for the 100 nC V and 1 uC V ranges since the charge lost during the 0 5 msec may be significant Too much current may also cause the digital accumulators to overload This occurs after 32 discharge charge cycles and is shown by sharp discontinuities in the Charge vs Time plot as the charge drops to zero Graphics Menu Single Graph displays the Charge vs Time plot as the default plot The Anson plot Charge vs sqrt Time can be selected using the Data Type drop down list box in the Graph Options dialog box Analysis Menu The Auto option for Results Graph displays the plot selected in Data Type and the slope intercept and correlation coefficient are listed in the Main window Since data at early time points can be distorted due to the finite time required for the potential step the Auto option uses only the last 80 of the data An alternative line can be defined by the use
99. tir functions on the BAS Controlled Growth Mercury Electrode CGME can be controlled manually or through the CV 50W In addition the knock and dispense routines required for the SMDE and CGME modes are controlled by the CV 50W and the Cell Stand option in the Setup dialog box must be set appropriately Data Link This port is used to communicate with the external PC via the cable and one of the serial communication ports COM ports on the PC via a standard RS 232C cable 2 5 2 2 Installation of Replacement ROMs in the CV 50W a b c d e PC BOARDS A Analog Board B I O Board C CPU Board Remove white plastic board support Item 1 Loosen four designated screws Item 2 on card rack and slide card retainer plates outward Remove necessary ribbon cables Item 3 by pressing ejectors outward from connectors and remove Remove the old CPU board bottom board by pressing ejectors Item 4 outward and pulling boards straight out NOTE Many of the large scale integrated circuits are static sensitive DO NOT place on plastic e g bubble pack carpeting or other surface which may have static build up Lay CPU board Figure 2 3 on a flat surface Components of the CPU board are sensitive to static Do not lay the board on carpeting plastic e g bubble wrap or other surfaces that build up static charge 2 6 Figure 2 3 CPU Board f Carefully pry ROM 1 out of its s
100. ud Rate This specifies the rate at which information is transferred between the PC and the potentiostat 2 10 Line Freq This specifies the line frequency of the local A C voltage The selected frequency determines the default Sample Width for pulse experiments Cell Stand The CV 50W can control the purging and stirring for BAS Cell Stands and the BAS Controlled Growth Mercury Electrode CGME The knock dispense routines for the SMDE and CGME modes of the Mercury Electrode are also controlled by the CV 50W so the Cell Stand option must be set accordingly The other parameters in the Setup dialog box are discussed in Section 3 see page 3 4 Once the Setup communication parameters have been checked the potentiostat can be powered up The system is now ready for use Printer Plotter Configuration Although a printer plotter can be selected using the Print Options dialog box see Section 9 2 the appropriate driver must first be installed The drivers for older models of printers plotters are contained on the Windows 3 x disks and are installed using the Printer dialog box in the Control Panel However the drivers for more recent models have to be provided by the printer manufacturer and require a different method of installation however explicit instructions are typically provided with the printer so installation should cause no problems 3 File Menu 3 1 File Dialog Box The CV 50W software uses standard Windows file dialo
101. ue charge to voltage converter for chronocoulometry Hardware interfaces with Voltammetric Cell Stand and Controlled Growth Mercury Electrode Control of stirring inert gas purging and mercury drop knock amp dispense Multiple experimental runs and averaging Automatic and manual peak finding routines Anson and Cottrell plots Laser printer and digital plotter output Multiple data set display and printing Digital smoothing by Moving Average and Least Squares Integration differentiation semi integration and semi differentiation Background subtraction Standard math operations Data storage binary and text formats Macro capability Specifications VO Cell stand port Data link port Potentiostat Output compliance voltage Applied voltage range Minimum potential step size Absolute accuracy Reference input impedance Maximum output current Risetime Slew rate Stability Effects of 10 input power line variation Noise and ripple Current to Voltage Converter Maximum current Ranges Fullscale output Custom port for control of BAS Cell Stands and Controlled Growth Mercury Electrode RS 232C serial port for communication between CV 50W and remote PC 10 volts minimum 3 276 volts to 3 276 volts 100 microvolts 2 5 millivolts gt 10 ohms 190 milliamperes lt 2 microseconds 10 Volts microsecond minimum 500 microvolts day 100 microvolts maximum 100 microvolts RMS maximum 190 millia
102. were used initially Since 3 digit run numbers are used in the data filenames it may be necessary to rename data files before reprocessing It should also be noted that the first run number is now 001 not O as in previous versions of the CV 50W software 8 Graphics Menu This Menu is used to display the experimental data after the experimental run and after any post run data processing 8 1 Single Graph The Single Graph window displays the experimental data Figure 8 1 The size and position of this windows can be changed by the user by dragging the caption or the borders and are defined initially by the CVSOW INI file CY Graph CV UNA Figure 8 1 Single Graph window The Single Graph windows can be displayed automatically at the end of an experiment and after a data file has been loaded the Find peaks check boxes in the Results Options dialog box need to be unchecked The data are graphed according to the Data Type specified in Graph Options or according to the default Data Sets In addition to the Single Graph the Single Graph window also displays the coordinates of the mouse cursor as it is moved within the axes Pressing the right mouse button leaves a plus mark on the graph the coordinates of which are also displayed A selected area can be expanded Zoomed by dragging the mouse between diagonally opposite corners of the defining rectangle This operation can be reversed by clicking the left mouse button 8 1
103. zed species Analysis Menu The Auto option for Results Graph displays the same plot as Single Graph and Init i End i i ratio Time Total Q and Net Q are listed in the Main window Net Q is the Total Q minus the background Q where the background i is assumed to be End i 10 38 11 Service and Troubleshooting 11 1 Preventative Maintenance Routine maintenance for the CV 50W consists of making certain that the forced air cooling systems are cleaned and checked regularly Forced air is employed for both the power supply and circuit board enclosure The cooling air inlet and air filter are located on the front panel A routine inspection perhaps weekly in a dusty area is required for the filter Cleaning is required if the filter has trapped dust and lint on its surface or is turning white in color The filter is not removable for cleaning but can be easily cleaned with a vacuum cleaner equipped with a brush accessory Be sure that the CV 50W power switch is off before cleaning so that the internal fans do not pull in dust that is dislodged during filter cleaning If a fan operates in a sluggish noisy or abnormal way then replacement is recommended Periodically examine both internal and external cables and wires for damage to the insulation or connectors and replace as needed Periodically check the system for loose screws brackets fans etc tighten as necessary 11 2 Troubleshooting When intermittent or unusu

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