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Potentiostat Book - Measurement Systems Ltd

1. 1 Hz Square Front Panel Wave Back Panel Overload Overload 10 MQ veroad detector Error UL a oe Voltage E E In Ausi L 100 ka uxiliary O x10 L5 O Command Power Amp V 100 kQ voltage Ground CO y Ref Amp A E Out faced No Reference Reference O 3 Hi Z iR Comp O voltage Shield O y do lg 25 E PGA Dac HO lOu Working O ii o lto V Bie Shield D H C Input O Call 12 Control p nterface r Online 1 C Output The Potentiostat is fitted with an internal 1 MQ dummy cell for use in potentiostat or galvanostat mode The dummy cell is physically connected whenever the Real cell mode is not being used The Potentiostat has gain ranges at decade intervals from 1 nA V to 10 mA V provided by an to V convertor and PGA The maximum current output signal I Out is 10 V at any gain setting Secondary amplification of the current signal is done by the e corder The gain and secondary amplification are set by the single range menu in the software which offers a combined total of 21 current range settings from 20 nA to 100 mA in 1 2 5 steps page 102 The Potentiostat uses an error amplifier to compare the difference in potential between the reference electrode and the excitation potential set using the analog output of the e corder The output of this amplifier provides an error signal the feed back circuit tries to zero The coaxial shields of t
2. el Range Amplitude 1 000V Al a fo E Stimulator Constant Output Figure 5 3 Using the Scope Stimulator Triangle command Cancel J Ce Stimulator Mode Delay 18 00ms A a ii Duration 15 00ms A cua pea Pulses 2 Amplitude 0 800 A CE E gt 64 eDAQ Potentiostats Thus by setting the data acquisition rate to be as fast as possible for a particular experiment you will also ensure that the waveform has steps that are as small as possible When performing FCV a large background charging current is often recorded This can be many times larger than the signal you are looking for Fortunately the charging current is usually reproducible between scans and can be subtracted from the final result 1 first a background scan is obtained with a blank solution that is a solution containing only the background electrolyte 2 next a scan is performed of the solution in which the substrate is present and finally 3 the Scope page that contains the background scan is selected using the Display gt Set Background command which will subtract this scan from all other pages in the file Use the Display gt Don t Subtract Background command to cancel subtraction and Clear Background to cancel the subtraction and clear the background sweep The background scan must be run under the same conditions sweep width and stimulator settings
3. 0 E i 1 0 05 1999 95 1 0 1 Stimulator settings to produce a 500 mV high 0 5 Hz square wave el ea ll eee Potential waveform generated by these settings Analysis of Chronoamperometry Chronoamperomograms obtained from a planar disk electrode should exhibit a current time relationship governed by the Cottrell equation see Appendix D for definition of terms z nFAC D 1000 xt It is usually easier to first simplify the Cottrell equation thus j 2 aft where a is treated as an empirical constant to be determined 70 eDAQ Potentiostats Figure 5 11 Typical chronoamperometric data analyzed using the Arithmetic channel calculation and the X Y window 5 56034 Y Current E 0 5500 Y E E E E E 5 3 o ies 3 5 2 o gt 0 8761 gt kag Wisan O window HH Typical experiment with 1 vVt data calculated on Channel 3 using the Arithmetic channel currenti Region of ideal linear response Cottrell graph of current versus 1 y t prepared in the XY Window Deviations from linearity typically occur at very 2 small and very large t values You can use the Chart s Arithmetic channel calculation see the Chart Software Manual to create data on an unused channel usually Channel 3 according to the equation Channel 3 1 Sqrt SampleTime You can now use the X Y window to p
4. O O z 200 l e Select output range EcincerA 68 eDAQ Potentiostats Figure 5 9 Adjusting potential with the Chart Timed Events feature Macintosh only To adjust the potential you will first need to select the range by choosing the Output Voltage command in the Setup menu to activate the Stimulator Constant Output dialog box Figure 5 8 The smaller the selected output range the finer the control that you will have when you adjust the potential The Timed Events Setup menu feature and macros can be used to keep the potential constant for a fixed period of time or to drive the reaction backwards by applying an opposite potential to perform an oxidation reduction cycle The Chart software Stimulator command in the Setup menu can also be used to set up pulses stepped pulses and staircase ramp waveforms for the Potentiostat or Picostat See the Chart Software Manual for more details You can also use the Timed Events feature Setup menu to adjust the current at predetermined time intervals after the start of recording For example the settings shown in Figure 5 9 will maintain a potential of 1 25 V for 30 minutes after which the potential will be decreased to 0 50 V in order to reverse the reaction resulting in a Double Step Chronoamperometric experiment Any number of steps at any potential could be set up with this feature However Timed Events can be slightly delayed by up to 0 1 s depending on the mod
5. Picostat or QuadStat controls cannot be accessed in Chart Scope or EChem software that is only the standard Input Amplifier dialog box of the e corder can be accessed e Check that the Online indicator is illuminated after the software has been opened If not then proceed as in the previous problem e Check that you have connected the E In Out and E Out cables correctly to the appropriate e corder connectors The Overload indicator is on a potential overload has occurred e Check that the electrode cables are firmly attached to the electrodes e Check that the surfaces of the electrodes have not become fouled e The Picostat or QuadStat Overload indicators may come on when the software is started this is normal The Overload indicator light should go out when you open the Picostat or QuadStat controls or start recording e See page 8 page 28 or page page 43 for more details The current signal goes off scale e Increase the full scale current range setting e Make sure each electrode is connected to the correct lead wire page 7 page 27 or page 43 e Make sure the electrodes and the alligator clips connecting them to the lead wires are not touching each other e Decrease the surface area of your working electrode e Decrease the concentration of the background electrolyte e Decrease the concentration of the substrate e Check that a potential overload see previous section has no
6. The Applied Potential controls are enabled when either the Dummy or Real cell is selected It allows you to adjust the voltage applied to either the dummy cell or external electrodes depending on the mode selected gt 7 Level 0 0004 FY Applied Current a Y Set applied current as baseline The Applied Current controls appear when in Galvanostat mode replacing the Applied Potential controls see Figure 5 17 page 78 The controls are enabled when either the Dummy or Real cell is selected Use them to adjust the current applied Figure 5 19 page 79 On Windows computers the gt button advises on the correct values to be entered into Units Conversion of the current signal channel see Figure 5 18 page 78 Chapter 2 The Potentiostat 21 Applied potential Range Range 2 Y When using Chart software on a Windows computer the Range control limits the range over which the applied potential can be set Smaller ranges offer finer control with the slider bar of the applied potential Figure 2 7 In Galvanostat mode this control changes so as to limit the range over which the applied current can be set Figure 5 17 page 78 On a Macintosh computer use the values in Range control are affected by the selection in the Stimulator Constant Output dialog box Figure 5 8 page 68 and Table 5 1 page 81 Re mem be r Pote n ti a set applied potential as baseline Check the set applied potential as
7. Pause Resume Axis expansion Invert current scrolling contraction signal Chapter 2 The Potentiostat 15 NOTE When using early models of EA161 Potentiostat serial numbers 161 001 to 161 022 as a ZRA you should connect the working electrode lead and the cable of the Grounding Connector page 10 to the two electrodes or circuit test points across which to measure the current operation is required the auxiliary and reference leads red and yellow should be attached to the single counter electrode e Galvanostat Chart and Scope software page 77 82 Connect the electrodes as described for potentiostat operation above Note especially that the potential signal is provided at Out Figure 2 3 The current signal is provided at E Out e ZRA zero resistance ammeter Chart and Scope software Connect the working green and auxiliary red leads to the two electrodes or circuit test points across which to measure the current the current signal is provided at Out The auxiliary red lead is earth return The reference lead yellow can be connected to a reference electrode or circuit test point to measure the potential difference to the auxiliary and working leads The high impedance potential signal if used is supplied at E Out Figure 2 3 e High Z high impedance voltmeter Chart and Scope software Connect the working green lead to one electrode and the reference lead yellow lead to a refe
8. Techniques 67 Figure 5 7 Chart Setup menu Macintosh Figure 5 8 Chart Stimulator Constant Output voltage controls Macintosh Chart macros can be used to keep the potential constant for a fixed period of time or to drive the reaction backwards by first applying one potential and then subsequently applying a second potential to perform an oxidation reduction cycle Refer to the Chart Software Manual for more information On Macintosh If you are using a QuadStat then most constant potential experiments between 2 5 V are done by adjusting the internal QuadStat Applied Potential page 57 If you require applied potentials greater than 2 5 V or pulsed waveforms then you can use the Chart Stimulator controls as described below Chart software can be used to output a constant potential up to 10 V which the Potentiostat Picostat or QuadStat will apply at the working electrode These controls are accessed through the Setup menu Figure 5 7 Display Settings Channel Settings SY Trigger Zero All Inputs Use the Stimulator command to access the Stimulator applied potential waveform controls Stimulator Stimulator Panel Output Voltage Configure Digital Output Digital Output gt Timed Events Use the Output Voltage command to set the baseline potential Figure 5 8 Auto Comments 10 V Stimulator Constant Output 5 _ e 2 Range 1V i H vi Amplitude V SOE
9. The electrode connector of the Picostat provides connection pins for the Working Auxiliary and Reference electrodes The connector also provides connections for shields which protect the signals in the cable wiring from electrical interference noise pickup The pin assignments of the Picostat Electrode connector are shown in Figure 3 2 The Working and Reference electrode leads have coaxial shields which are maintained at the respective electrode potentials to minimise lead capacitance Lenan Electrode connector 6 pin Lemo socket to electrodes Overload indicator light O Overload Picostat Ne y Online indicator light Alignment dot Working Electrode Auxiliary Electrode Working Electrode Shield Not connected Reference Electrode Reference Electrode Shield 26 eDAQ Potentiostats Table 3 1 Color coding on the leads of the electrode cable Color Electrode Yellow Reference Green Working Red Auxiliary Electrode Cable The Picostat is supplied with a three lead electrode cable with each lead terminated by an alligator clip The Reference and Working electrode leads are shielded to protect the signals from external interference The alligator clips allow connection to a wide variety of electrodes The leads are color coded to indicate the type of electrode to which they should be attached Table 3 1 For normal three electrode us
10. and or Mains Filter to minimise high frequency noise on the signal especially if you are working outside a Faraday cage You can now adjust the applied potential with the slider bar or by entering the exact potential with text entry The resulting current signal should obey Ohm s law E R so that with the 100 MA test resistor R in place an applied potential E of 1 V should produce a current of 10 nA while other potential settings should produce corresponding currents Picostat Control Window With Chart software the Picostat Control window is accessed from the Picostat command in the Channel Function pop up menu Figure 3 7 shows the control window on a Windows computer and Figure 3 8 on a Macintosh computer These windows control the various current ranges and filtering options for the Picostat With Scope software the corresponding controls are shown in Figure 3 9 Signal Display The current signal is previewed scrolling across the display area Note that the signal is not being recorded to hard disk at this stage and that when the window is closed the signal trace is lost Chapter 3 The Picostat 35 Figure 3 9 Accessing the Picostat controls with Scope software Use the Picostat button ma Range 100n4 ow Picostat m2 y Pause Resume Select input scrolling range Select low pass filter Low Pass 10Hz Standby Real Set Applied P
11. as the substrate solution to be effective See the Scope Software Manual for more information Chronoamperometry with Chart Chronoamperometric techniques require that a constant potential is maintained for a defined period while the current is monitored If the current signal is integrated with respect to time then the total charge transferred at the electrode can be calculated Chronocoulometry page 75 Single double and even multi step chronoamperometry can be performed with Chart or Scope software in a time frame from a millisecond to hours or even days if need be For experiments involving sudden changes in potential you should use the full bandwidth of the Potentiostat or Picostat or QuadStat that is if possible do not use the low pass filters or the response of the current signal may be modified by the low pass filter time response characteristics Chapter 5 Techniques 65 On Windows computers If you are using a QuadStat then most constant potential experiments between 2 5 V are done by adjusting the internal QuadStat Applied Potential page 57 If you require applied potentials greater than 2 5 V or pulsed waveforms then you can use the Chart Stimulator controls as described below Chart software can be used to set a constant voltage of up to 10 V which is known as the command voltage from the e corder Output This is sent to the Picostat or Potentiostat or QuadStat via the E In input cabl
12. such as an unconnected or faulty electrode or the resistance is too high in the electrochemical cell Higher resistances can be often be encountered when electrodes are fouled by the products of electrolysis reactions The Picostat tries to compensate by increasing the compliance potential that is the potential between the auxiliary and working electrodes If the compliance voltage exceeds specification about 13 V potential control of the cell is lost and drifting or oscillation of the signal can be seen Any data collected during this period is unreliable and should be discarded The Picostat Overload indicator will remain lit once an overload has occurred it will be reset once the scan has finished If the indicator comes on repeatedly and your connections are good then try bringing your electrodes closer together and or increasing electrolyte concentration and or modifying your experimental conditions to avoid fouling of the electrodes Redesigning you electrochemical cell may be necessary Normally electrochemical cells are designed to keep the reference and working electrodes very close together however when a potential overload occurs you also need to consider the distance between the auxiliary and working electrodes NOTE A potential overload is quite different from a current overload condition A current overload is caused when the current signal exceeds the full scale limits of the sensitivity setting of the current c
13. 50 Using Multiple References and Auxiliaries First Use 52 QuadStat Control Window 54 QuadStat Potential Window 58 Maintenance 59 eDAQ Potentiostats iii 5 Techniques 61 Introduction 62 Linear Scan Techniques 63 Fast Cyclic Voltammetry 63 Chronoamperometry with Chart 65 On Windows computers 66 On Macintosh 68 Analysis of Chronoamperometry 70 Chronoamperometry with Scope 74 Chronocoulometry 75 Chronopotentiometry 77 Chart software on Windows computers 79 Chart software on Macintosh 80 Scope software 82 Controlled Potential Electrolysis 82 Controlled Current Electrolysis 83 Amperometric Sensors 84 Biosensors 85 Microdialysis Sensor 86 Dissolved Oxygen dO Sensors 86 Nitric Oxide NO Sensors 87 A Technical Aspects 89 Potentiostat 89 Picostat 91 QuadStat 92 B Troubleshooting 95 C Specifications 101 Potentiostat 101 104 106 Picostat QuadStat D Electrochemical Equations 109 Linear Sweep and Cyclic Voltammetry 109 Chronoamperometry 111 Chronocoulometry 112 Index 113 License 8 Warranty 117 eDAQ Potentiostats NOTE This manual is for the EA161 Potentiostat If you have an older model EA160 Potentiostat then please ask us to send you the appropriate manual C HAPTER ONE Overview There are three eDAQ potentiostat models e Potentiostat EA161 Chapter 2 Single channel three electrode potentiostat galvanostat with gain ranges of 20 nA to
14. Ch 1 Ch 2 Ch 3 Ch 4 Input 2 4 6 8 Figure 4 7 for actual J appearance E In Output It is not always necessary to monitor E Out depending on your experimental requirements Connections to E In are only required if using an external waveform to control the applied potential Use Output to send a signal of reverse polarity to the QuadStat 48 eDAQ Potentiostats Figure 4 7 The QuadStat shown connected to an e corder front view using the connections described in Table 4 2 a Cl x A NA Nu CARCAN AS Auxiliary and reference Use one two three or Note that the cable from the electrode leads from four working electrodes e corder Output is not required for Channel 1 Use these when constant potential experiments the working electrodes are to between 2 5 V be used in the same reaction vessel and a single auxiliary and reference electrode are required See also Figure 4 8 be applied at the working electrode Such an arrangement is shown in Figure 4 7 If you need to reverse the polarity of the QuadStat use e corder Output With these connections when you use the software to set a more positive voltage a more reducing potential will be applied at the working electrode By linking the E In positions with short wires you can control the potentials of all electrode potentials simultaneously Figure 4 6 Check that all connectors are firmly attached Loose connec
15. Figure 2 5 and Figure 2 6 To operate the Potentiostat with the reverse polarity make the connections as shown in Table 2 3 With these connections when you use the software to set a more positive voltage a more reducing potential will be applied at the working electrode Check that all connectors are firmly attached Loose connectors can cause erratic behaviour or may cause the Potentiostat to fail to work eDAQ Potentiostats The Potentiostat uses two e corder input channels during normal operation The reminder of this chapter assumes that you have connected the current signal to e corder Input Channel 1 and the potential signal to e corder Input Channel 2 It is possible when using Chart or Scope software to connect the Potentiostat to other e corder input channels in which case the description that follows would change accordingly When using EChem software Channel 1 is always set to be the current signal the channel and Channel 2 is automatically set to be the potential signal the E channel Thus when using EChem software you must always connect the current signal Out to Input Channel 1 and the potential signal E Out to Input Channel 2 of the e corder Channel 2 normally displays the applied potential and its settings are controlled using the standard Input Amplifier dialog box described in the Chart Software Manual and Scope Software Manual which are installed as pdf files in the eDAQ Documentation folder on y
16. Manual Grounding Connector The Potentiostat back panel Figure 2 3 has a 4 mm grounding socket This enables connection of a Faraday cage with the green grounding cable included with the Potentiostat the use of which can greatly diminish electrical noise The Potentiostat is supplied with a green colored ground cable terminated with a 4 mm pin attaches to Potentiostat back panel and an alligator clip for attachment to Faraday cage If your Faraday cage is already earthed by its own ground connection then you should not use this cable otherwise a second pathway to earth would exist which could result in a ground loop and increased signal interference You can try grounding the Faraday cage via its own connection to earth or via the Potentiostat ground cable but not by both methods simultaneously eDAQ Potentiostats Table 2 2 Potentiostat to e corder connections as shown in Figure 2 5 and Figure 2 6 Table 2 3 Potentiostat to e corder connections reverse polarity The construction of the Faraday cage can range from a simple cardboard box covered with aluminium foil in which the electrochemical cell is located to a more sophisticated copper mesh enclosure or sheetmetal box But in all cases it is essential that the Faraday cage be electrically grounded to act as an effective shield against electrical interference The Potentiostat itself is grounded via its connection to the e corder unit which is in
17. OK the QuadStat will revert to Standby mode until recording is started For now select the Dummy cell mode which connects an internal 1 MO resistor between the electrodes You will need to adjust the gain range to 5 pA to accommodate your signal amplitude If the signal is noisy select the 10 Hz low pass filter and or Mains Filter You can now adjust the applied potential with the slider bar or by entering the exact potential with text entry The resulting current signal should obey Ohm s law E R so that with a 1 MO test resistance R an applied potential E of 1 V should produce a current of 1pA while other potential settings 52 eDAQ Potentiostats Figure 4 9 Accessing the QuadStat controls with Chart software Windows Figure 4 10 Accessing the QuadStat controls with Chart software Macintosh y J1004s FJ 100 nA Turn Channel Off Picostat Computed Input Units Conversion Channel 1 X QuadStat amp Quadstat 1 Drag ticks and labels to adjust axis scaling Select QuadStat from the Channel Function pop up menu Applied potential value 0 97 p Current signal display area 4 Applied Potential Level 0 000 Set applied potential as baseline Remember applied Slider bar for setting potential applied potential Select QuadStat from the Channel Turn Input Off fe to00 s 200msi Function pop up menu fy R
18. Potential 10 0000 Y OK IV Set applied potential as baseline when dialog is closed Cancel Select range for Remember applied Slider bar for setting Enter applied applied potential potential applied potential potential as text m oos 2000 Select Picostat from the Channel 1 fy Range 100 n 5 aa Function pop up menu Turn Channel Off Computed Input p Units Conversion Drag ticks and E Select input labels to adjust axis range v No Calculation Picostat Select low pass filter Range 100 nA 3 Select Real Low Pass 10 Hz or Standby mode O Standby O Real Applied Potential V Enter y Applied j 1 1 1 w 10 Potential Slider bar a for setting Mains Filter z T 2111 a applied Invert j potential Units f Cancel Cox gt Pause Resume Axis expansion Invert signal Set mains filter scrolling contraction 34 eDAQ Potentiostats not recognised the Picostat Exit the software check all your connections and try again By default the control window opens with the Picostat in Standby mode that is with the reference and working electrodes isolated so that no current will flow through your electrodes To connect to the Picostat lead wires you must select Real mode When you click Cancel or OK the Picostat will revert to Standby mode until recording is started You will need to adjust the gain range to 20 nA to accommodate your signal amplitude and to select the 10 Hz low pass filter
19. Quadstat apply a potential difference across a pair of working and reference electrodes whilst monitoring the current flow between the working and auxiliary electrodes This potential difference is determined by a command voltage which is sent from the e corder output to the E In connector of the Potentiostat Picostat Figure 3 3 on page 29 Potentiostat Figure 2 4 on page 9 or QuadStat Figure 4 2 on page 44 The QuadStat can also generate a constant command voltage internally Chart and Scope software control the e corder output via the Stimulator controls in their Setup menus For a full description of these controls and the waveforms that can be produced you should consult the Chart Software Manual and Scope Software Manual You can use your e corder and Potentiostat Picostat or QuadStat with Chart and Scope software to perform the following experiments Linear Scan techniques page 63 use Scope software with the Potentiostat to provide a potential ramp up to 500 V s and to subtract charging current contributions The bandwidth of the Picostat and QuadStat are sufficient for scan rates up to about 10 V s e Chronoamperometry page 65 amp page 74 Amperometry Constant Potential Electrolysis page 82 monitor the current signal at fixed potentials e Chronocoulometry page 75 monitor and integrate the current signal at a fixed potentials e Chronopotentiometry page 77 Constant Current Electrolysi
20. a 2 Potentiostat a PIRA 50 gt Computed Input E 2 Units Conversion v No Calculation Arithmetic El Cycle Variables Units No Reset X Range z Range Picostat 100 n Reset Cancel lt p gt Computed Input for Channel 1 Raw Data Input nme J integral 0 245n4 1 34n4A s 5 Range 100 ma 4 ELA Turn Channel Off Potentiostat Computed Input Units Conversion 74 1 ynduy ag Syu suueyo i 8 4 v No Calculation Smoothing Arithmetic No Reset 5 Cycle Variables Differential Range 2onvs a Integral Display Computed Functions Display ChA amp B w Display Settings Axis Labels Channel A Channel B Go To Page 6 Smooth Go Smooth go Show Overlay Overlay None 38H Matt None 7 Matn None Overlay Display Settings Subtract Background Set Background Clear Background Function Integrate w Function Ch A Integrate Input A Select Integrate in the Function menu Overlay Stimulator Computed Functions 3F gt 76 eDAQ Potentiostats command in the Channel Function pop up menu further details are in the Chart Software Manual This is particularly useful when you want to recalculate the integral from the original curren
21. accesses the Stimulator dialog box which when using galvanostat mode allows a baseline and various current waveforms to be configured Figure 5 19 Always select an appropriate current range for your system While it is possible to set an applied current of up to 100 mA the Potentiostat Galvanostat cannot supply a potential much greater than 10 V Even relatively small applied currents with a highly resistive load may require potentials in excess of this If in doubt start with a small test current and observe the resulting potential Potentiostat Waveform Document1 Stimulator Mode Pulse pe Output Continuous Marker channel Off Zi Number of Pulses A Stat When recording starts Delay 0 0 H ms Manually Set Number of Pulses Stimulate Range PPM Hz Output Range cc E When in Galvanostat mode the Stimulator 7 J controls are used to adjust the applied current Compare with Potentiostat mode where the Stimulator is used to adjust applied potential Figure 5 6 Y Frequency Amplitude DA Baseline 250 00 p Chapter 5 Techniques 79 Figure 5 20 Setting up the Potentiostat as a Galvanostat Macintosh With highly resistive loads using a large range setting with a small close to zero current can produce unexpected large potential signals because of small offsets in the current control circuitry If you require very small currents always us
22. all reasonable efforts to fix them This service may incur a charge depending on the nature of the problems and is subject to the other conditions in this Agreement Hardware Warranty eDAQ Pty Ltd warrants the Potentiostat or Picostat to be free of defects in material and workmanship for one year from the date of purchase eDAQ Pty Ltd will repair or replace defective equipment as appropriate To obtain a warranty repair replacement you must first notify us before return of the instrument and we License amp Warranty will issue you with a RAN return authorization number You must ship the defective product at your expense We will pay return shipping The product should be packed safely preferably in its original packaging and have the RAN on the shipping label Returns sent without a RAN may be refused delivery This warranty does not cover hardware that has e been modified by the user in any way e been subjected to unusual physical electrical or environmental stress This includes damage due to faulty power sockets inadequate earthing or power spikes or surges e been damaged because of incorrect wiring to ancillary equipment or because of substandard connectors or cables or e had the original identification marks removed or altered Software License You have the non exclusive right to use the supplied eDAQ software Chart Scope etc Your employees or students for example are entitled to use it
23. analysis 70 Chart Macintosh 68 Windows computers 66 multiple step 67 70 74 Scope 74 chronocoulometry 75 112 chronopotentiometry 77 compliance 84 Cottrell equation 70 75 111 integrated form 112 current signal calibration Potentiostat 19 current signal zero QuadStat 57 curve fitting 72 cyclic voltammetry 61 63 109 D differential pulse voltammetry 61 dissolved oxygen sensor 86 Dummy cell Potentiostat 18 QuadStat 56 eDAQ Potentiostats 113 E E In connector Picostat 29 Potentiostat 9 QuadStat 45 E Out connector Picostat 29 Potentiostat 9 QuadStat 45 EChem software 1 61 eDAQ Amps 2 Bridge Amp 2 GP Amp 2 pH Amp 2 Picostat 2 Potentiostat 2 QuadStat 2 eDAQ potentiostats 1 electrochemical equations 109 electrode cable Picostat 27 Potentiostat 7 QuadStat 42 electrode connector Picostat 26 pin assignments 26 Potentiostat 6 pin assignments 6 QuadStat 42 electrode leads color coding Picostat 27 Potentiostat 7 QuadStat 42 shielding Picostat 27 Potentiostat 7 QuadStat 42 electrolysis controlled current 83 controlled potential 82 electropolymerisation 83 84 electrosynthesis 83 84 F Faraday cage grounding cable Picostat 30 Potentiostat 10 QuadStat 46 Faraday s constant 111 fast cyclic voltammetry 63 fast linear sweep voltammetry 63 front panel Picostat 26 Potentiostat 6 QuadStat 42 G galvanostat 62 setting current values 77 galvanostat mode 77
24. are close Fitting complete in 1 Channel 1V iteration s Ba Time s F t a sqrt t o b SSE 12 368 _R 0 99935 Select Fit cues e Jp enough then a curve of better fit with new vales for a and b will be obtained Unlock c and iterate again A curve of best fit should be obtained Chapter 5 Techniques 73 and the Curve Fit extension are installed Remember to operate the Potentiostat or Picostat at full bandwidth that is do not use the low pass filters if possible or else your results may be dominated by the low pass filter response Chronoamperometry with Scope For chronoamperometric measurements where you need to overlay the results of successive experiments Scope will generally be the program of choice The total length of the experiment is chosen in the Time Base panel Up to 2560 data points can be collected in a period of up to 128 s long You should normally use the full bandwidth of the Potentiostat or Picostat that is do not use the low pass filters or the response of the Use the Stimulator command to access the Figure 5 13 Sampling Stimulator applied potential waveform controls Stimulator Scope controls for Ta multiple step chronoamperometry L Stimulator Constant Output Use he Output manges 3 Vo aia Pi
25. be attached Table 2 1 For normal three electrode potentiostat page 15 or galvanostat page 16 use the reference electrode must never be connected to either the auxiliary red or working green leads otherwise the current that would be passed through the electrode could effectively destroy it as a reference potential source When two electrode potentiostat or galvanostat operation is required the auxiliary and reference leads red and yellow should be attached to the single counter electrode The green lead is attached to the working electrode When using in ZRA zero resistance ammeter mode connect the working green and auxiliary red leads to the two electrodes or circuit test points across which to measure the current page 16 The reference lead yellow can be connected to a reference electrode or circuit test point to measure the potential difference to the auxiliary and working leads When using High Z high impedance mode connect the working green lead to one electrode and the reference lead yellow lead to a reference electrode to measure the potential difference between the leads page 16 The auxiliary lead red can be connected to a third Chapter 2 The Potentiostat electrode or test point to provide a ZRA current signal at E Out Figure 2 3 The Online Indicator Located at the bottom right of the front panel is the Online indicator Figure 2 1 When lit it indicates that
26. been set up to go from 1 00 to 1 00 V and back again over a period of 40 ms using the Up amp Down waveform option This corresponds to a scan rate of 50 V s Figure 5 3 shows an example of a positive and negative cyclic waveform The base potential has been set to 0 20 V and a potential ramp has been set up to go from 0 20 to 0 80 V back again to 0 40 V and finally return to 0 20 V over a period of 20 ms using the Triangle waveform option This corresponds to a scan rate of 120 V s The Triangle waveform option always starts a scan in the centre of the potential limits while the Up amp Down waveform option starts a scan at one or the other of the potential limits Ideally FCV requires a smooth analog ramp and so it is desirable to make the steps in the applied waveform output as small as possible The e corder output is controlled by a DAC digital to analog convertor is the value of which is updated whenever a new data point acquired Chapter 5 Techniques 63 Use the Stimulator command to access the Stimulator applied potential waveform controls Figure 5 1 Sampling app P Scope Setup menu Stimulator Output Yoltage Use the Output Voltage command to set the baseline potential E Stimulator Constant Output Figure 5 2 Using the Scope Cancel J Stimulator Up and Down command Stimulator Mode Up Down Delay 20 00ms A Duration 40 00ms A amo Il as iA
27. eDAQ web site at www eDAQ com If the experiment requires a differential pulse methodology then the MuliPulse Amperometry techniques of the EChem software can be used for various pulse amperometric experiments See the EChem Software Manual for more details Biosensors Biosensors are often amperometric sensors and so can be used with the Picostat QuadStat or Potentiostat which can then be referred to as biosensor meters The first step is to establish the polarising voltage and current measurement requirements of your sensor Chapter 5 Techniques 85 The QuadStat also has the ability to zero or offset a background current signal which can be of use when trying to amplify small peaks on a large background signal see Zero Offset page 57 Many biosensors provide a linear signal response over a range of concentrations but deviations occur over wider concentration ranges The Chart software Multiple Point Calibration extension can be used to extend the useful range over which a biosensor can be used by compensating for a non linear signal response Microdialysis Sensor The Sycopel Microdialysis Biosensor is available in several configurations for both in vivo or in vitro detection of analytes including glutamate glucose glycerol ascorbate and acetylcholine The Picostat and QuadStat have suitable current ranges for use with this sensor and Chart software would normally be used to record data The QuadStat a
28. in a flow injection analysis experiment or during in vivo neurotransmitter monitoring The QuadStat has six gain ranges from 100 pA V to 200 pA V in 1 2 5 steps The maximum current output signal Out is 10 V at any gain setting Secondary amplification of the current signal is done by the e corder The gain and secondary amplification are set by the single range menu in the software which offers a combined total of eleven current range settings from 2 nA to 1 mA in 1 2 5 steps The coaxial shields of the RE and WE lead wires which carry a high impedance signal are maintained at the same potential as the lead wire to minimise electrical interference and reduce lead capacitance The QuadStat is powered is powered by regulated 17 V 17 V and 8 V DC lines from the e corder see Figure 4 4 on page 45 The use of DC power allows its use inside Faraday cages Multiple electrode potentiostat designs for sensor work have been reported in Development of a computer controlled multichannel potentiostat for applications with flowing solution analysis Tang Fang Michael McGrath Dermot Diamond and Malcolm R Smyth Analytica Chimica Acta 305 347 358 1995 94 eDAQ Potentiostats APPENDIX B Troubleshooting This appendix describes some problems that may arise when using the Potentiostat Picostat or QuadStat There is also help in your e corder Manual and Software Manuals located on the eDAQ S
29. on the back panel of the e corder and the other the other end to the 12C Input connector on the back panel of the QuadStat The QuadStat provides two signals per channel the potential signal E Out indicating the potential difference between the working and reference electrodes and the current signal Out indicating the current flow between the working and auxiliary electrodes Use the BNC cables with bare wires at one end to connect the terminal strip Figure 4 3 as described in Table 4 2 and Figure 4 5 or Figure 4 6 Note there are several possibilities depending on how many of the QuadStat channels you wish to use and whether you require the use of the e corder Output or an external waveform generator For experiments where the working electrode potential is held constant between 2 5 V the E In pin positions are unused Figure 4 5 If the electrode potential required is greater than 2 5 V or is to be pulsed or ramped during the experiment then the E In input must be connected to a suitable external signal such as from the Output of the e corder or a waveform generator Figure 4 6 If an e corder is used then normally connect to Output With these connections when you use the software to set a more positive voltage a more oxidising potential will QuadStat rear panel e corder front panel Table 4 2 QuadStat to e corder Out Ch 1 Ch 2 Ch 33 Ch 4 Input 1 3 5 7 BNC connections See E Out
30. range Table 5 1 80 eDAQ Potentiostats Table 5 1 Galvanostat current range settings of the Potentiostat as a function of e corder output range Galvanostat Current Ranges e corder Output Potentiostat Galvanostat primary gain Range 100 nA V 1 pA V 10 pA V 100 pA V 1 mA V 10 mA V 10V 1 pA 1 mA 10 mA 100 mA 5V 500 nA 500 pA 5 mA 50 mA 2V 200nA 2pA 20pA 200pA 2mA 20 mA 1V 100 nA 1 pA 10pA 100 pA 1 mA 10 mA 500 mV 50 nA 500 nA 5 pA 50 pA 500pA 5 mA 200 mV 20 nA 200 nA 2 pA 20 pA 200 pA 2 mA Usually it is better to use the corresponding setting elsewhere in the table cable will be carrying the potential signal which will now appear on Channel 1 and the E Out cable the current signal which will now appear on Channel 2 When you start to record data you will find that the Units Conversion on Channel 2 has been set to appropriate value so that the signal is automatically displayed with the correct current units The default setting is to have the applied current on the 100 mA range It is likely that there will be a small residual offset at this setting which will cause the Potentiostat Galvanostat to go off scale over 10 V in Standby mode as it is connected to the relatively low resistance 10 Q internal dummy cell Try selecting a more appropriate 1 pA or 10 pA range where the offset will be correspondingly smaller an
31. s O ain E e L voltage 570 a au Ref Am E Out Shield O d t j Error Voltage gt C Reference Reference QHe Hi Z ye voltage Bical low pass Filter o 9 tO Out i PGA Working e j F a 2 E Offset Shield O DAC EG Input gt 12 Control A DAC ha Interface To QuadStat channels 2 3 and 4 Online 2C Output which is applied to the Counter electrode CE in such a way as to minimise the error voltage The QuadStat and the electrochemical cell to which it is connected form a composite feedback control system in which the value of the Counter Electrode CE voltage is controlled in such a way as to make the Reference voltage with respect to the Working electrode voltage equal to the desired Command voltage The current flow I in the Working Electrode WE is the quantity being measured When the QuadStat is in Standby mode the CE and RE are disconnected from the cell and connected to an internal dummy cell This prevents current flowing through the electrochemical cell and allows a simple test of circuit operations A steady state or transient overload condition is indicated when the error voltage exceeds a small non zero value This indicates that the system could not establish or sustain a balanced state The Overload light will be reset when scanning is stopped or when the QuadStat controls are next accessed
32. smaller potential reduces sensitivity but is usually more selective for oxygen Most oxygen sensors exhibit a slow response time and will take at least several seconds to stabilise Thus you would normally employ a 1 10 Hz filter setting on the Potentiostat QuadStat or Picostat in order to minimise any electrical noise The Mains Filter setting can also be employed to further reduce mains hum Sampling rates of about 1 s are usually optimal The QuadStat also has the ability to zero or offset a background current signal which can be of use when trying to amplify small peaks on a large background signal see Zero Offset page 57 If you intend to monitor oxygen concentrations over a wide range then you can calibrate the electrode at several concentrations and use the Chart software Multiple Point Calibration extension to compensate for a non linear electrode response You can download the extension from www edaq com Nitric Oxide NO Sensors Most polarographic nitric oxide sensors can be used with the Picostat or QuadStat which are suitable for detecting the small currents expected from the low concentrations of nitric oxide found in natural biological systems Most commercial nitric oxide sensors comprise a carbon fibre anodic working electrode to which the working electrode lead is attached and a cathodic counter electrode to which the reference and auxiliary electrode leads are attached Usually an oxidising polarisin
33. the e corder and or the QuadStat IMPORTANT The QuadStat is a highly sensitive current measuring device To prevent damage by static discharge always make sure you are earthed before touching the QuadStat Electrode connectors connecting the lead wires or before you connect the lead wire alligator clips to the electrodes You can do this after first connecting the QuadStat and e corder by touching the outer casing of the e corder or QuadStat This will connect you to earth via the electrical grounding of the instrument and any static charge you have collected will be dissipated eDAQ Potentiostats 41 Figure 4 1 The QuadStat front panel Working Electrode connectors BNC Channel 1 Channel 2 Channel 3 Channel 4 QuadStat 164 Auxiliary Electrode Reference Electrode Online Overload connector 4 mm socket connector BNC indicator indicator light light The Front Panel The front panel of the QuadStat is shown in Figure 4 1 Electrode Connectors The front panel of the QuadStat provides connections for the Working WE Auxiliary AE and Reference RE electrodes BNC connectors are used for the WE and RE leads The shields of these connectors are driven to the same potential as the electrode The connector for the AE lead is a socket for a 4 mm pin Electrode Cables The QuadStat is supplied with appropriate electrode cables with each lead terminated by an alligator c
34. your experiment If during the experiment the current signal exceeds the range then the data will be truncated and therefore lost Low pass Filtering Mains filter The QuadStat has low pass filter settings 10 kHz to 1 Hz for removal of high frequency signals noise The Off setting gives the full bandwidth of the QuadStat which can be up to 16 kHz but which may also be limited by the characteristics of your electrodes and sample solution The 10 Hz filter settings and less are highly effective for the removal of mains hum 50 or 60 Hz interference and as a general rule should be employed whenever possible However low pass filters should be used with care when performing pulse amperometric or voltammetric experiments or for other signals which are likely to exhibit fast rise or fall times For example if you are using the 10 Hz filter then applied potential pulses should be longer be longer than 100 ms and voltammetric experiments should have scan rates scan rates less than about than 100 mV s otherwise excessive smoothing of the signal may occur Chapter 4 The QuadStat 55 When you use the Chart and Scope software there is a Mains Filter checkbox If this is ticked then the e corder will apply a mains filtering algorithm to the incoming signal which removes repetitive signals occurring at 50 or 60 Hz which are typical of mains interference Note that the mains filter is NOT a simple notch filte
35. 1 nA V and 10 nA V The maximum current output signal Out is 10 V at any gain setting Secondary amplification of the current signal is done by the e corder The gain and secondary amplification are set by the single range menu in the software which offers a combined total of eleven current range settings from 10 pA to 100 nA in 1 2 5 steps The coaxial shields of the reference and working electrode lead wires which carry a high impedance signal are maintained at the same potential as the lead wire itself to minimise electrical interference and reduce lead capacitance QuadStat The QuadStat is comprised of four subunits which function in potentiostat mode only that is the QuadStat cannot be used as a galvanostat A block diagram of the QuadStat construction is shown in Figure A 3 Within the QuadStat an error voltage is generated from the difference between the voltage on the Reference electrode and the sum of the excitation command voltage set provided at E In and the voltage provided by the E Offset DAC This error voltage drives a high gain amplifier VCVS voltage controlled voltage source the output of 92 eDAQ Potentiostats Figure A 3 Block diagram of the QuadStat Channel 1 Front Panel Gvel cdD lecior Back Panel Overload o Power Amp Subtractor E In Auxiliary ot
36. 100 mA e Picostat EA162 Chapter 3 Single channel three electrode high sensitivity potentiostat with gain ranges of 10 pA to 100 nA and e QuadStat EA164 Chapter 4 Four channel three electrode potentiostat with gain ranges of 2 nA to 1 mA with current signal offset They are a part of the family of fully software controlled modular preamplifiers DAQ Amps which are designed for use with the e corder system Some of the uses of the Potentiostat Picostat and QuadStat are mentioned in Chapter 5 and also in the EChem Software Manual which describes the use of the optional EChem software eDAQ Potentiostats How to Use this Manual This manual describes how to set up and begin using your Potentiostat Chapter 2 Picostat Chapter 3 or QuadStat Chapter 4 Their use with Chart and Scope software is also described Chapter 5 The appendices provide technical and troubleshooting information See the EChem Software Manual for a description of the use of these potentiostats with the optional EChem software eDAQ Amps The Potentiostat Picostat and QuadStat are part of a family of preamplifiers known as eDAQ Amps The Potentiostat Picostat and QuadStat are designed for performing voltammetric and amperometric experiments As with other eDAQ Amps they are designed to be operated under full software control and are automatically recognised by Chart Scope or EChem software which control their gain ran
37. 4 x 5 9 x 7 9 inches Weight 1 5 kg 3 3 lb Operating conditions 0 35 C O 90 humidity non condensing eDAQ reserves the right to alter these specifications at any time Appendix C Specifications 107 108 eDAQ Potentiostats APPENDIX D Electrochemical Equations Linear Sweep and Cyclic Voltammetry The Randles Sevcik Equation For a substrate with a reversible redox reaction at a planar disk electrode in an unstirred solution the peak current during linear sweep or cyclic voltammetry is given by the Randles Sevcik equation A 269n2AD 2cv 2 for an oxidation anodic scan A 269n 2 AD 2Cv2 for a reduction cathodic scan The potential where this occurs is given by 0 0285 a 0 0285 Eb E a Eb gt Er E where ip Current peak during anodic scan A ip current peak during cathodic scan A E potential at current peak for anodic scan V E potential at current peak for cathodic scan V E1 half potential as determined by cyclic voltammetry V n the number of electrons transferred to or from the substrate molecule A area of the exposed surface of the electrode cm eDAQ Potentiostats 109 D diffusion coefficient of the substrate molecule cm2 s C concentration of the substrate molecule mol L the scan rate V s The factor of 269 is a parameter that derives from using a planar electrode at a temperature of 298 K Th
38. If the reaction causes the formation of a polymer film on the electrode for example pyrrole to polypyrrole or aniline to polyaniline then the technique may be referred to as electropolymerisation To effect the electrolysis of a substrate a potential should be chosen which is at least 50 200 mV more oxidising or reducing than the half wave potential in order to ensure complete reaction It is usually important to separate the auxiliary counter electrode from the main body of the electrochemical cell by means of a salt bridge This is to prevent the reduction products formed in the region of the auxiliary electrode reacting with the products of oxidation at the working electrode or if reducing the substrate to prevent the products of oxidation forming around the auxiliary electrode from reacting with the reduction products at the working electrode The working electrode is usually constructed to have relatively large surface area so that a greater amount of material can be electrolyzed in a small time thus a plate or gauze electrode is usually chosen although reticulated vitreous carbon RVC which has an open pore foam structure is also a popular choice The conversion of large amounts of substrate gt 100 mg in reasonable times requires relatively high currents to be passed through the cell Thus the Potentiostat maximum current 100 mA is usually more suitable than the Picostat lt 100 nA or QuadStat lt 1 mA channel f
39. Potentiostat Picostat amp QuadStat a N a Lenao EX gt Overload O Overload P O P O a N Channel 1 Channel 2 Channel 3 Channel 4 QuadStat 164 O we we we we AE 0 sO AE 0 HOR q O RE RE RE RE O O O O O O y e corder www eDAQ com This document was as far as possible accurate at the time of printing Changes may have been made to the software and hardware it describes since then eDAQ Pty Ltd reserves the right to alter specifications as required Late breaking information may be supplied separately Latest information and information and software updates can be obtained from our web site Trademarks of eDAQ e corder and PowerChrom are registered trademarks of eDAQ Pty Ltd Specific model names such as e corder 201 PowerChrom 280 Picostat and QuadStat are trademarks of eDAQ Pty Ltd Chart and Scope are trademarks of ADInstruments Pty Ltd and are used under license by eDAQ EChem is a trademark of eDAQ Pty Ltd Other Trademarks Mac OS and Macintosh are registered trademarks of Apple Computer Inc Windows 98 Windows Me Windows 2000 and Windows XP are trademarks of Microsoft Corporation PostScript and Acrobat are registered trademarks of Adobe Systems Incorporated All other trademarks are the properties of their respective owners Products Pot
40. Potentiostat 16 Potentiostat electrode connection 7 GP Amp 2 ground loop 10 31 47 grounding connector Picostat 30 Potentiostat 10 QuadStat 46 H high impedance voltmeter Potentiostat 7 16 High Stability Potentiostat 18 High Z mode Potentiostat 16 Potentiostat electrode connection 7 Out connector Picostat 29 Potentiostat 9 QuadStat 45 114 eDAQ Potentiostats 12C connector Picostat 29 Potentiostat 10 QuadStat 46 input amplifier 13 33 50 integrated Cottrell equation 112 iR Compensation 103 Potentiostat 20 L lead wire capacitance 26 42 linear scan techniques 63 linear sweep voltammetry 61 109 M Mains Filter 98 mains hum 98 maintenance Picostat 39 Potentiostat 22 QuadStat 59 microdialysis sensor 86 multiple step chronoamperometry 67 70 74 N nitric oxide sensor 87 noise 10 30 46 98 normal pulse voltammetry 61 O Offset QuadStat 57 Ohm s law 22 35 52 59 Online indicator Picostat 27 Potentiostat 8 QuadStat 43 Overload indicator Picostat 28 Potentiostat 8 QuadStat 43 P pH Amp 2 Picostat 2 polarity Picostat 32 Potentiostat 12 QuadStat 49 polyaniline 83 polypyrrole 83 potential overload 84 Potentiostat 2 electrode connection 7 modes of operation 15 problems 95 pulsed amperometry 61 Q QuadStat 2 QuadStat Applied Potentials window 58 R Randles Sevcik equation 109 Real cell Picostat 38 Potentiostat 18 QuadStat 56 reference ele
41. The RE voltage is measured by a high input impedance amplifier whose output is summed with the WE potential to provides a low impedance output to the e corder unit proportional to the actual potential difference between the RE and WE Appendix A Technical Aspects 93 The WE is held at a virtual potential by a voltage to current convertor The different WE s can be individually adjusted that is the virtual potential can be adjusted over a range of 2 5 V with the internal E Offset DAC In particular note that the E Offset adjustment affects the potential of the WE but that a signal applied at E In affects the potential of the RE and AE However for most applications it is only the potential difference between the RE and the WE that is important When using multiple working electrodes in a single reaction vessel with a common reference and auxiliary a waveform signal applied to E In of the auxiliary reference channel will affect the potential difference to all the working electrodes Thus for example a triangular waveform to the E In will effectively cause all working electrodes to perform cyclic voltammetry For further details see Using a Common Reference and Auxiliary page 50 The current signal each working electrode is measured by a separate current to voltage convertor The signal can be zeroed by means of an offset current this is useful in situations where a large background current is present as might occur
42. adjustment or Option click on Macintosh Each QuadStat channel can have a different amount of offset applied to its current signal The maximum amount of offset available is 400 pA on ranges of 2 pA or more and 400 nA on ranges of 1 pA or less The amount of current offset is reported in the text box 0 00ua If you need to zero the current signals after recording has started then you can use the Zero All Inputs command in the Chart software Setup menu QuadStat Potential Window When using the QuadStat with Chart software on a Windows computer it is possible to alter the working electrode during recording Access the QuadStat Applied Potentials window Figure 4 12 from the Chart Setup menu Working electrode potentials can then be adjusted independently on each connected QuadStat channel This is equivalent to adjusting the potentials using the Applied Potential controls page 57 in the QuadStat Control Window Figure 4 9 on page 53 except that adjustments can be made while recording is in progress Display Settings Channel Settings Ctrl Y Trigger Zero All Inputs QuadStat Potential Stimulator Stimulator Panel Event Manaos Timed AdgOTE CN Cla Dp irr Chit Ley 5 QuadStat on Input 1 QuadStat on Input 3 QuadStat on Input 5 QuadStat on Input 7 58 eDAQ Potentiostats It is also possible to automate the QuadStat Potential controls with the Ma
43. and software without notice No liability can be accepted for consequential damages resulting from use of eDAQ products 118 eDAQ Potentiostat
44. ange 1 m v Drag ticks and Start stop scrolling Select input Select low pass filter Set mains O Standby O Dummy Real K V offset 0 000 u Cancel Click to manually adjust zero offset Controkclick for fine control Computed Input F labels to adjust axis Select cell Select input range Units Conversion Y QuadStat E Input 1 dStat 0 001 mA Range 1ma ia A 7 Select low ae a 3 Low Pass Off pass filter O standby Mi Offset A O Dummy o o00pa f ulozero z O Real ao current E signal M Applied Potential V 0 e pa a ia Y Set the a 2 5 0 25 A Y Applied Potential aid Mains Filter Invert Units f Cancel gt Cox gt Pause Resume Axis expansion Invert signal Set mains filter scrolling contraction Chapter 4 The QuadStat 53 Figure 4 11 Accessing the QuadStat controls with Scope software Click the QuadStat button Select input range QuadStat Pause Resume scrolling Input 1 QuadStat 0 001 m ao E ee Select low its a 0 far oe eS Low Pass i Current signal pass filter o alg Standby i Offset display area SO aooaa Autozero 0 a J E Pi Zero current E e a op mog En o IV Applied Potential 4 a Ci E f 0 000000 y Applied Potential J Mains Filter Set mains I Invert fi
45. at will remain connected to the dummy cell even when the QuadStat Control window is closed and Chart Scope or EChem is recording This is useful for testing the QuadStat Real In Real mode the electrodes will be active and the Applied Potential slider control can be used to adjust the potential When you close the control dialog using EChem software the QuadStat will revert to Standby mode until the Start button is clicked to begin a scan If you are using Chart or Scope software the QuadStat will 56 eDAQ Potentiostats remain in Real mode when the dialog is closed this allows you to start and stop recording data while the electrodes remain active which allows periodic recording of the signal from amperometric biosensors or in vivo electrodes without disturbing the environment around the electrodes Please note that when using multiple working electrodes in the same reaction vessel with a single reference and single auxiliary electrode make sure that all the QuadStat channels are set to the same value Standby Dummy or Real Running an experiment with some channels set on Dummy while others are on Real Standby can cause incorrect current signals V Applied Potential Level 0 000Y Applied Potential J V Set applied potential as baseline The Applied Potential control offsets the voltage up to 2 5 V applied to either the dummy cell or external working electrodes This potential Eo
46. baseine box to remember the value of the applied potential when the Potentiostat control window Figure 2 7 page 14 is closed The potential value is transferred to the Stimulator baseline control Figure 5 5 page 67 Maintenance The Potentiostat will not require maintenance during daily operation However you should periodically check the instrument for optimum results by switching to potentiostat mode with iR Compensation off and applying a known potential E to the Dummy Cell and checking that the resulting current signal value l is in accordance with Ohm s law E R where R is the resistance and is 1 MQ for the dummy cell Thus a signal of 1 pA should be obtained when a potential of 1 V is applied 1 pA with 2 V etcetera Try several different potentials and make sure an appropriate current signal is observed in each case If this test produces the expected results then your Potentiostat is likely to be functioning correctly Next use the Potentiostat in Real Cell mode to check the electrode cables by attaching them to a resistor usually a resistor of 103 108 Q is ideal with the working electrode lead on one side of the resistor and the auxiliary and reference leads connected to 22 eDAQ Potentiostats the other If the current signal does not obey Ohm s law then it is likely that the electrode leads have become damaged However if both the Dummy Cell and Real Cell tests produce the expected results but y
47. cially at the alligator clips where they are subject to mechanical wear Use a multimeter to ensure that the clips are still in good electrical contact with the correct pins in 98 eDAQ Potentiostats the input connector of the electrode cable see Figure 2 2 on page 6 Figure 3 3 on page 29 and Figure 4 2 on page 44 Also check that the shield pins have not shorted to any of the alligator clips e Ensure that the reaction vessel and electrodes are positioned as far as possible from power leads computers monitors and other mains powered equipment Ideally the reaction vessel and even the Potentiostat or Picostat should be enclosed by a Faraday cage A Faraday cage or other electrical shielding is almost always required when measure small currents which is usual with the Picostat e Random spikes occurring during your experiment are more likely to be due to nearby electrical equipment switching on and off Equipment with high current drain such as electric motors in vacuum pumps refrigerators or air conditioner compressors should be particularly suspect Try turning such equipment off during your experiment to identify the source of the problem You may have to change your location try a power socket on another circuit in the same room or even move rooms completely Appendix B Troubleshooting 99 100 eDAQ Potentiostats APPENDIX C Specifications Potentiostat Power Am
48. cluding any signal due to any small offset from the e corder Output at E In Thus it should be considered a relative zero Recalibatrion is required after you e select a different range for the Potentiostat applied potential page 21 e turn iR Compensation on or off page 20 e change from Potentiostat to ZRA operating mode e change from ZRA to Potentiostat operating mode However to get true absolute current measurements in Potentiostat mode independent of small offsets at E In first calibrate in ZRA mode and then switch to Potentiostat mode without recalibrating Note that in all cases the Calibrate button does NOT remove background current signals due to actual electron flow in the real cell iR Compensation Level 0 000 ohms H C Test iR Compensation iR compensation is available only when in Potentiostat mode Positive feedback compensation is used When the iR Compensation panel is on then the degree of iR Compensation can be adjusted using the slider bar First adjust the applied potential to a value where no Faradaic process occurs use the buttons for fine control Now use the slider bar to gradually increase the amount of compensation until the current signal goes into oscillation then decrease the compensation until stability is restored For very fine control of iR Compensation use the Test checkbox This applies a small perturbation 1 Hz 10 mV amplitude square wave to the electrode The
49. costat or QuadStat When using the Potentiostat as a galvanostat the applied current can be set within ranges up to 100 mA Select the smallest range setting consistent with your desired current to ensure maximum accuracy For example if a current of 750 pA is required then a range setting of 1 mA 1000 pA should be used and then exact current value adjusted accordingly Chapter 5 Techniques 77 Figure 5 17 Setting up the Potentiostat as a Galvanostat Windows Figure 5 18 The Current channel units conversion dialog box The current values used should ensure that the resulting potentials do not exceed 10 V the maximum limit of the Potentiostat highly resistive loads can easily produce large potentials even with small currents Remember that when setting zero or very small currents there is always a small amount of offset error in the system If you are trying to measure the potential of a system under zero current conditions then it would generally be more accurate to use a zero current potentiometer or pH meter than a galvanostat or use the Potentiostat in High Z mode page 16 EE Select Potential signal is displayed Turn Channel OFF Potentiostat in when in Galvanostat mode Computed Input the Channel Select the expected range Units Conversion menu for the potential signal Potentiostat Potentiostat 1 Range Low pass fiov v 10 kHe if 0 003 Y Cell Mode O S
50. cro feature of Chart so that the working electrode potentials can be altered at predetermined times Please consult the Chart Software Manual installed in the e DAQ Documentation folder on your hard disk for more information about the use of Macros Maintenance Your QuadStat will not require maintenance during daily operation However you should periodically check the QuadStat for optimum results by applying a known potential E to the Dummy Cell Open the QuadStat Control window Figure 4 9 or Figure 4 10 and go to Dummy Cell mode The current signal should obeys Ohm s law E R where R is the resistance and is 10 Q for the dummy cell and E is the applied potential Thus a signal of 1 pA should be obtained when a potential of 1 V is applied Try several different potentials and make sure an appropriate current signal is observed Repeat this procedure on the different QuadStat channels If this test produces the expected results then your QuadStat is likely to be functioning correctly Also periodically repeat this procedure with the electrode cables connected and attached to a test resistor as described in the section on First Use page 52 If the current signal does not obey Ohm s law then first recheck your connections of the QuadStat to the e corder page 48 If the problem persists then it is possible that the electrode leads or the QuadStat itself has become damaged If these tests indicate that the QuadStat i
51. ctrode aging and regeneration 98 S sensors amperometric 84 biosensors 85 dissolved oxygen 86 microdialysis 86 nitric oxide 87 signal offset QuadStat 57 signal zero QuadStat 57 Index 115 specifications Picostat 104 Potentiostat 101 QuadStat 106 square wave voltammetry 61 Standby cell Potentiostat 18 QuadStat 56 static discharge 25 39 41 T Timed Events 69 82 two electrode operation Picostat 27 Potentiostat 15 Potentiostat electrode connection 7 QuadStat 42 V voltammetry cyclic 61 109 differential pulse 61 fast cyclic 63 fast linear sweep 63 linear sweep 61 109 normal pulse 61 square wave 61 Z zero offset 57 zero resistance ammeter Potentiostat 16 ZRA mode Potentiostat 16 Potentiostat electrode connection 7 116 eDAQ Potentiostats gt O Overload Potentiostat e Trademarks e corder and PowerChrom are registered trademarks of eDAQ Pty Ltd All eDAQ software hardware and documentation is protected by copyright eDAQ retains the exclusive ownership of the trademarks and registered trademarks represented by its company name logo and product names Responsibilities You and any others using any eDAQ product agree to use it in a sensible manner for purposes for which it is suited and agree to take responsibility for their actions and the results of their actions If problems arise with an eDAQ product eDAQ will make
52. d electropolymerization reactions are often more quickly carried out under constant current conditions than under constant potential conditions but there is a greater risk of side reactions occurring as the potential changes Ideally there should no competing redox reactions at nearby potentials A sudden change in the potential usually indicates when the substrate is fully consumed It is important to limit the current so that the potential stays within the compliance voltage 10 V of the Potentiostat Galvanostat at least until the reaction of interest is complete Electropolymerization reactions can be problematic as a non conducting polymer film adhering to the working electrode will increase its electrical resistance causing the Potentiostat to eventually go out of compliance and experience a potential overload Amperometric Sensors Amperometric sensors require a potentiostat of appropriate gain range Your will also need to determine whether the sensor is of a two or three electrode configuration The Potentiostat up to 100 nA Picostat up to 100 nA and QuadStat up to 1 mA can be used in three electrode mode working reference and auxiliary electrode or in two electrode mode working and counter electrodes by connecting the reference and auxiliary leads of the electrode cable together You will also need to determine the correct polarising voltage to use with your sensor 84 eDAQ Potentiostats The polari
53. d the signal should come on screen and be close to zero volts The e corder Output Voltage can be set as described earlier Figure 5 8 on page 68 At each of these Output Voltage range settings the Potentiostat offers four current range settings when in Galvanostat mode Table 5 1 The most accurate control is achieved by using the largest possible Output Voltage range with the smallest possible Galvanostat range setting Adjust the current within the selected range The resulting potential signal is shown in the display area Chapter 5 Techniques 81 During an experiment control the applied current is by adjustment of the Output Voltage controls Chart Setup menu this controls the e corder output voltage which in turn controls the current applied by the Galvanostat For example if you have selected an e corder Output Voltage range of 500 mV and a current range of 50 pA Table 5 1 you might now wish to do an experiment where the current is held at a constant 35 pA or 35 50 x 100 70 of the range setting You should now set the slider control of the Output Voltage control to a value of 70 of 500 mV that is to 350 mV A positive or negative Output Voltage determines the direction of current flow into or out of the working electrode The Chart software Stimulator command Setup menu can also be used to set up pulses stepped pulses and staircase ramp waveforms which the galvanostat will follow You can also use t
54. e the reference electrode must never be connected to either the auxiliary or working leads otherwise the current that would be passed through the reference electrode could effectively destroy it as a reference potential source If two electrode operation is required the auxiliary and reference electrode leads red and yellow can be attached to the single counter electrode The green electrode lead is attached to the working electrode When attaching the cable to the Picostat make sure that the red dot on the cable connector is aligned with the red dot on the Picostat Electrode Connector Figure 3 2 Insert the cable connector and push gently until it locks into position To remove the cable pull the cable connector gently until it disengages Do NOT twist the connector The Online Indicator Located at the bottom right of the front panel is the Online indicator Figure 3 1 When lit it indicates that the software such as EChem Chart or Scope has located and initialised the Picostat If the light does not go on when the software is run check that the Picostat is properly connected If there is still a problem please refer to Appendix B Troubleshooting page 95 Chapter 3 The Picostat 27 The Overload Indicator Located on the left hand side of the front panel is the Overload indicator Figure 3 1 When lit this indicates that the Picostat has gone out of compliance which usually occurs because of an open circuit
55. e which then applies this potential across the reference and working electrodes The software controls are accessed through the Stimulator command in the Setup menu Figure 5 4 To adjust the command voltage you will first need to select the range by adjusting the Output Range control in the Stimulator controls Figure 5 5 The smaller the selected output range the finer the control that you will have when you adjust the potential with the Baseline control To monitor the current signal at a constant potential 1 set the Stimulator to Pulse mode 2 set the Pulse Amplitude to zero volts 3 set the Baseline control to the desired voltage A adjust the current input range to an appropriate value page 17 and page 36 5 set the speed of recording that is the number of data points to be collected per second to an appropriate value you will usually require at least several hundred data points over the lifetime of your experiment The Chart Software Manual has detailed descriptions on setting the recording speed and finally 6 begin the experiment by clicking the Start button in the main Chart window The Stimulator command can be used to alter the applied potential with a precision better than 1 ms Pulses up to 30 s long may be created by this method For further details on using the Stimulator in Chart refer to the Chart Software Manual An example using the Chart Stimulator is shown in Figure 5 6 Note that the pulse amplitudes ar
56. e a small range setting as well this will ensure a minimum offset error For example to apply a current of only 25 nA use the 100 nA range setting for best results Chart software on Macintosh Galvanostat mode of operation is accessed by choosing the Potentiostat command in the Channel Function pop up menu to open the control window Turn on the Galvanostat and Dummy radio buttons Figure 5 20 When in Galvanostat mode the current and potential signals will be reversed from normal potentiostatic operation That is the Out Select Potentiostat in y 1007s 200m5 Div the Channel menu fy Range 100 n a Select the expected range for the potential signal Select galvanostat gt operation Computed Input 4 Units Conversion A Potentiostat Y Input 1 Potentiostat 1 Nel 0 0065 Y Range 10 V Bl y i i E f a Potential ignal Low Pass 10 kHz 1 isplay area T O Standby O Potentiostat e Galvanostat mode pa Dummy Galvanostat 7 pig oT TT ami a a a Real D ZRA gt o 0 O High Z i f M High Stability 9 Ad ia E Applied Current pA Set J TER p applied 1 1 1 1 Q 8 oe oe oe ee El o f current vw Lui bn Range 1pA u ugh a _ iR Compensation Q _ Test v 0 0 10 C Mains Filter M invert Units Cancel The four Galvanostat current range settings in this menu are dependent on the e corder Output Voltage
57. e added to any value set by the Baseline control eDAQ Potentiostats Figure 5 4 Chart Setup menu Windows Figure 5 5 Chart Stimulator waveform output controls Windows Figure 5 6 Stimulator controls for multiple step chronoamperometry Windows Display Settings Channel Settings Ctrl V Trigger zero Al I Use the Stimulator command to access the Stimulator L applied potential waveform controls Figure 5 5 amp Figure 5 6 Stimulator Stimulator Panel Select stimulator mode Stimulator 1 Document1 Continuous Set Number of Pulses Number 1 H Stimulate Output Range 2Y H Amplitude ooy f Range C PPM Hz Select output range oH f Enter exact values as text Use zero amplitude for constant output Frequency Baseline control can be used for constant output drag slider controls to adjust value Stimulator Marker or y Stimulator 1 Document1 Mode Pulse Se Continuous Set Number of Pulses C He Output Range 1Y y Amplitude 500 00 mv g Range PPM ii ES Frequency Baseline 200 00 mv fs Settings to produce a 500 mV amplitude 1 Hz square wave on a base potential of 200 mV Pulse Duration 500 00 ms E Hoa we ce nee ie A Stimulator Marker for X A LI LI 400 Potential waveform generated by the Stimulator settings above Chapter 5
58. e are sudden potential jumps Chapter 2 The Potentiostat 17 Inverting the Signal 1m The Invert checkbox allows you to reassign the direction up or down of an anodic or cathodic current Please note that this affects the display of the signal only it does not reverse the direction of actual current flow at the electrodes Cell Cell Control 2 O Dummy Real The Potentiostat can be in one of three cell modes controlled by the Cell radio buttons e Standby If Standby mode is selected the electrode lead wires are disconnected and the internal dummy cell is connected The external real cell is not connected until the Potentiostat Control window is closed and the Chart Scope or EChem Start button is clicked This mode is used if you do not wish to alter the state of the external cell until the method is actually performed The Applied Potential slider bar control is disabled in this mode e Dummy the Potentiostat is connected to the internal 1 MQ dummy cell You can then use the Applied Potential slider control to vary the voltage applied to the dummy cell The Potentiostat will remain connected to the dummy cell even when the Potentiostat Control window is closed and Chart Scope or EChem is recording This is useful for testing the Potentiostat Real the external electrodes are connected to the Potentiostat The Applied Potential slider control Figure 2 7 and Figure 2 8 can be used to set the pote
59. ect the Potentiostat Failure to do this may result in damage to the e corder and or the Potentiostat NEW FEATURES If you have used the older EA160 Potentiostat before then you will notice that the EA161 has new front and back panels and incorporates several new features iR compensation ZRA mode High Z mode and also has a High Stability option for stabilization of the Potentiostat in situations where oscillation would otherwise be encountered Signal accuracy and signal to noise ratio have also been improved Note that the EA161 Potentiostat now uses the same electrode cable as the EA162 Picostat eDAQ Potentiostats The Front Panel The front panel of the Potentiostat is shown in Figure 2 1 The Electrode Connector The electrode connector of the Potentiostat provides connection pins for the Working Auxiliary and Reference electrode lead wires The connector also provides connections for the lead shields which protect the signals in the cable wiring from electrical interference noise pickup The pin assignments of the Potentiostat electrode connector are shown in Figure 2 2 The Auxiliary and Reference electrode leads have Figure 2 1 nil The Potentiostat front Ga panel Electrode connector sad lemo socket indicator light O overload to electrodes Potentiostat NS Online indicator light Figure 2 2 Alignment dot The Potentiostat electrode Working Electrode Auxiliary E
60. el S Channel 4 Channel3 Chamnel2 Chamnel O scz z sz z sz z sz z ARO 60 ERE ed LE ZIRE o RUS 111 11 1111 1 111 1 11 13 Input Bus Output 5 10 15 20 DB 9 pin I C connectors 20 pin socket for screw terminal adaptor Figure 4 3 Input and output signals Channel 4 Channel 3 Channel 2 Channel 1 2 e 8 e 8 5 ca65055058055850 58630 O WU O WOW Oe WOW Oe WOW O Ele EE EEE EEEPEEEEEPE p 20 pin terminal adaptor Push firmly into socket 44 eDAQ Potentiostats Figure 4 4 The 12C connectors A WARNING The IC connectors are for the power and control of eDAQ Amps page 2 and should not be used for connection to any other device NOTE 1 The overload light may come on when a QuadStat channel is being used for a second third or forth working electrode and the corresponding reference and auxiliary electrode connectors are not being used see Using a Common Reference and Auxiliary page 50 Under these conditions this does NOT indicate abnormal operation NOTE 2 A potential overload is quite different from a current overload condition A current overload is caused when the current signal exceeds the full scale limits of the sensitivity setting of the current channel This is in turn due to a low resistance between the electrodes In some circumstances a current overload can also cause the QuadStat overl
61. el of computer and what else is happening in the computer operating system For accurate timing it is better to use the Chart Stimulator which is fully under the control of the internal e corder clock Timed Events Display Settings Time Action Channel Settings RY 0 00 Analog Output 1 25000 V 30 00 Analog Output 0 50000 V Trigger Zero All inputs Stimulator Stimulator Panel Output Voltage Configure Digital Output iat Set time to Start End Timed Events star End New Delete Cancel Co Automatic Comments Access Timed Events Changing the potential from the Setup menu after a period of 30 s Chapter 5 Techniques 69 Figure 5 10 Simulator controls for multiple step chronoamperometry Macintosh Using the Stimulator command Setup menu it is possible to send and monitor pulses with a precision better than 1 ms Figure 5 10 Pulses up to about 30 s may be created by this method For further details on using the Stimulator in Chart refer to the Chart Software Manual 0 Stimulator Stimulator Mode Pulse be 3 a Output continuously Marker channel Off O fixed number of pulses Number of pulses 1 Start when recording starts Delay 0 ms O manually Stimulate U Range 2 Hz E Range fiv Frequency Hz Amplitude V cn 5 8 115 i 1 1 i i Sus i i i 1 e 0 1 2 1 0 t Pulse Duration ms Baseline V gt 1000 A
62. electrically grounded to act as an effective shield against electrical interference The Picostat is supplied with a green colored ground cable terminated with a 4 mm pin attaches to Picostat back panel and an alligator clip for attachment to Faraday cage for this purpose The Picostat itself is grounded via its connection to the e corder unit which is in turn earthed 30 eDAQ Potentiostats Table 3 2 Picostat to e corder BNC connections Table 3 3 Picostat to e corder BNC connections reverse polarity via the three pin mains power connector It is of course important that the power socket that you are using is well earthed The purpose of this ground cable to the Faraday cage is to provide an easy means of grounding the cage please note that it is not for grounding the Picostat If your Faraday cage is already earthed by its own ground connection then you should not use this cable Use of the cable in this instance will provide a second pathway to earth which could result in a ground loop which can actually increase signal interference You can try grounding the Faraday cage via its own connection to earth or via the Picostat ground cable but not by both methods simultaneously Connecting the Picostat Your Picostat will have been supplied with an 12C cable DB 9 pin connectors at either end and three cables with BNC connectors at either end First make sure that the e corder is turned off Then connect
63. entiostat EA161 Picostat EA162 QuadStat EA164 Document Number UM EA161 2 4 1105 Copyright November 2005 eDAQ Pty Ltd 6 Doig Avenue Denistone East NSW 2112 Australia http www eDAQ com email info eDAQ com All rights reserved No part of this document may be reproduced by any means without the prior written permission of eDAQ Pty Ltd eDAQ Potentiostats 1 Overview 1 How to Use this Manual 2 eDAQ Amps 2 Checking the unit 3 2 The Potentiostat 5 The Front Panel 6 The Electrode Connector 6 Electrode Cable 7 The Online Indicator 8 The Overload Indicator 8 The Back Panel 9 E Out Out and E In Connectors 9 I2C Connectors 10 Grounding Connector 10 Connecting the Potentiostat 11 First Use 13 Potentiostat Control Window 14 Maintenance 22 3 The Picostat 25 The Front Panel 26 Electrode Connector 26 Electrode Cable 27 The Online Indicator 27 The Overload Indicator 28 The Back Panel 29 Contents E Out Out and E In Connectors 29 I2C Connectors 29 Grounding Connector 30 Connecting the Picostat 31 First Use 33 Picostat Control Window 35 Maintenance 39 4 The QuadStat 41 The Front Panel 42 Electrode Connectors 42 Electrode Cables 42 The Online Indicators 43 The Overload Indicators 43 The Back Panel 45 E Out Out and E In Connectors 45 I2C Connectors 46 Grounding Connector 46 Connecting the QuadStat 48 Using a Common Reference and Auxiliary
64. f the e corder usually Output is used Reverse the polarity of the Potentiostat by using e corder Output Chapter 2 The Potentiostat A WARNING The IC connectors are for the power and control of eDAQ Amps page 2 and should not be used for connection to any other device The Potentiostat provides two signals the current signal Out indicating the current flow between the working and auxiliary electrodes and the potential signal E Out indicating the potential difference between the working and reference electrodes Note that the E Out signal is inverted with respect to the applied potential For most situations Out is connected to e corder input channel 1 and E Out to e corder input channel 2 However when you are using Chart software and recording data from various sources on more that just two channels you may want to connect the Potentiostat to other e corder input channels 12C Connectors The Potentiostat back panel Figure 2 3 has two DB 9 pin I2C bus connectors labelled Input and Output The Input connector provides power to the Potentiostat and carries the various control signals for gain range and filter selection to and from the e corder A cable is provided with the Potentiostat for this purpose The pin assignments are shown in Figure 2 4 The Output connector can be used for the attachment of other eDAQ Amps More information about the 12C connector can be found in your e corder
65. ference and Auxiliary Often the QuadStat will be used with a single reference electrode RE and a single auxiliary electrode AE on QuadStat channel 1 with multiple working electrodes WE on some or all of the other QuadStat channels To monitor the applied potential signal for Channels 2 4 then on each channel with a working electrode connect the unused AE and RE sockets together You can use the extra AE and RE lead wires supplied with the QuadStat connecting the alligator clips to one another for this purpose see Figure 4 8 If the unused AE and RE sockets on Channels 2 4 on the front panel of QuadStat remain unconnected as shown in Figure 4 7 then e the applied potentials can be still adjusted as described below LJ g Channel Channel 2 Channel 3 Channel 4 QuadStat 164 T Cr OF Pa Channel 2 Qo da working lead to be connected to q NN BN second WE i gt 5 Channel 2 auxiliary and reference leads connected together Channel 1 auxiliary reference and working leads to be connected to AE RE and first WE 50 eDAQ Potentiostats e the current signals from the various working electrodes will still be correctly monitored however e the corresponding potential signals at E Out are not accurately monitored and the overload light may come on but this does NOT indicate a fault condition Only the overload light of Channel 1 where the reference and auxiliary electrodes a
66. g voltage Chapter 5 Techniques 87 applied potential of up to 1 0 V is required at the working electrode to effect the reaction NO 2H 0 gt NO 4H 3e The exact potential can be varied to suit the type of electrode many electrodes have special catalytic surface coatings the sample being measured and to minimise side reactions At potentials smaller than 0 7 V the current signal is usually dependent on the polarising voltage but between 0 7 and 1 0 V the current signal tends to plateau as the reaction is limited by the rate at which nitric oxide can diffuse to the anode surface At potentials greater than 1 0 V the hydrolysis of water gradually becomes the dominant source of the current signal Most nitric oxide sensors exhibit a slow response time and will take at least several seconds to stabilise Thus you would normally employ a 1 10 Hz filter setting in order to minimize any electrical noise The Mains Filter setting can also be employed to further reduce mains hum Sampling rates of about 1 s are usually optimal It is recommended in most cases to calibrate the electrode at several nitric oxide concentrations covering your range of interest Use the Chart software Multiple Point Calibration extension which can be downloaded from the eDAQ web site at www edaq com The QuadStat also has the ability to zero or offset a background current signal which can be of use when trying to amplify small peak
67. ge signal filtering and other settings The eDAQ Amp family also include the e pH Amp suitable for connection of pH ion selective and potentiometric ORP electrodes e Bridge Amp suitable for sensors requiring a DC Wheatstone bridge connection Also provides DC excitation e GP Amp suitable for high output sensors requiring a high impedance DC Wheatstone bridge Also provides DC excitation See our web site at www eDAQ com for more information eDAQ Potentiostats Checking the unit Before you begin working with the Potentiostat Picostat or QuadStat please check that e all items described in the packing list are included and that e there are no signs of damage that may have occurred during transit Contact your eDAQ distributor if you encounter a problem You should also become familiar with the basic features of your e corder system which are discussed in the e corder Manual which will be installed as a pdf file on your computer when you install the software Chapter 1 Overview eDAQ Potentiostats C HAPTER TWO The Potentiostat This chapter describes how to connect and use your model EA161 Potentiostat If you have an older model EA160 Potentiostat please refer to the documentation that came with your unit or contact eDAQ at support edaq com to obtain the correct document IMPORTANT Always make sure that the e corder is turned off before you connect or disconn
68. gure 3 4 The pin assignments for the Input IC DB 9 connectors 4 WARNING The I2C connectors are for the power and control of eDAQ Amps page 2 and should not be used for connection to any other device 12 control signals Power lines 12 control signals Q Q 508 Sos HO ae oe l og a 1 Po 2820 O BEBE 222 FF 2x2 U O lt XU_222 2223 o0Oxo0 E DD DD nD DD D Da as ZB89083022 2h Age snaBazZz SA O O O O O O O o O Y nput Output power to the Picostat and carries the various control signals for gain range and filter selection to and from the e corder A cable is provided with the Picostat for this purpose The pin assignments are shown in Figure 3 4 The Output connector can be used for the attachment of other eDAQ Amps More information about the 12C connector can be found in your e corder Manual Grounding Connector The Picostat back panel Figure 3 3 has a 4 mm grounding socket This enables connection of a Faraday cage with the green grounding cable included with the Picostat the use of which can greatly diminish electrical noise The construction of the Faraday cage can range from a simple cardboard box covered with aluminium foil in which the electrochemical cell is located to a more sophisticated copper mesh enclosure or sheet metal box In all cases it is essential that the Faraday cage be
69. h Level A SON Serie ce al baseline potential 0 50000 Y Ex Stimulator Sc IN Delay 10 0 s A Duration 30 0 s Pulses A2 Adjust the pulse pS a 100 120 waveform Ka Page 1 o gt spare d Range aja 0 70000 Y A 0 00000 Y a emplean y ps frequency 74 eDAQ Potentiostats current signal may be dominated by the low pass filter time response characteristics The base potential is adjusted with the Output Voltage command Setup menu shown in Figure 5 13 A potential that will cause the reaction to proceed and the period for which it will be applied is set using the Stimulator command In the example shown in Figure 5 13 after a period of 10 s at the base potential of 0 5 V two 30 s pulses of 0 70 V are to be applied each followed by a 30 s return to the base potential The experiment is usually first done on a blank solution containing only electrolyte followed by a sample solution containing the substrate The data is collected on separate pages in Scope and the blank data subtracted with the Set Background command You can then copy and paste the scan to a spreadsheet so that the differences can be plotted against 1 yt in a Cottrell graph For further details refer to the Scope Software Manual Chronocoulometry Chart and Scope software have the ability to integrate an incoming signal both online that is in real time as you are collecting data or offline that is after the experiment is completed Since t
70. hannel This is in turn due to a low resistance between the electrodes eDAQ Potentiostats Figure 3 3 The Picostat back panel BNC output BNC input connectors connector E Out 1 Out 4 mm socket E O P ground connection a J0 eJo 5 o Input us Output a N a AY DB 9 pin 12C connectors The Back Panel The back panel of the Picostat is shown in Figure 3 3 E Out Out and E In Connectors The Picostat back panel has three BNC connectors labelled E Out Out and E In The E In is connected to the Output of the e corder usually Output is used If you need to reverse the polarity of the Picostat use e corder Output The Picostat provides two signals the potential signal E Out indicating the potential difference between the working and reference electrodes and the current signal I Out indicating the current flow between the working and auxiliary electrodes For most situations Out is connected to e corder input channel 1 and E Out to e corder input channel 2 However when you are using Chart software and recording data from various sources on more that just two channels you may want to connect the Picostat to other e corder input channels 12C Connectors The Picostat back panel Figure 3 3 has two DB 9 pin IC bus connectors labelled Input and Output The Input connector provides Chapter 3 The Picostat 29 Fi
71. he Timed Events feature Setup menu to adjust the current at predetermined time intervals after the start of recording Consult the Chart Software Manual for more details of the Output Voltage Stimulator and Timed Events features Scope software Operation of the Potentiostat as a Galvanostat with Scope software is similar to using Chart software Macintosh version see page 80 However a wider variety of applied waveforms can be generated with the Scope Stimulator command Controlled Potential Electrolysis This technique is essentially the same as Chronoamperometry with Chart page 65 and is also known as amperometry A constant potential is applied at the working electrode which is sufficient to oxidize or reduce the substrate As the electrolysis continues the substrate is eventually completely consumed and the current will decrease to a residual value Both the potential and the current flow can be monitored with Chart software in the same way as for chronoamperometry The integrated current that is the total charge transferred can also be determined by integrating the current signal see Chronocoulometry page 75 and this can be used to determine the extent of reaction 82 eDAQ Potentiostats If the solution is being stirred during the procedure then eventually all the substrate can be oxidized or reduced to a new material and the technique may be referred to as electrosynthesis rather than chronoamperometry
72. he current signal is drifting significantly or is greater than 5 pA then contact your eDAQ representative it is possible that stray static discharge may have damaged the Picostat s electrometer chip Also periodically repeat this procedure with the electrode cable connected and attached to the 100 MA test resistor as described in the section on First Use page 33 If the current signal does not obey Ohm s law then first recheck your connections of the Picostat to the e corder page 31 If the problem persists then it is possible that the electrode leads or the Picostat itself has become damaged If these tests indicate that the Picostat is working correctly but you are still experiencing difficulties with your experiments then you should now check the electrodes you are using the connections to them and the design and condition of the reaction vessel and any salt bridges that you are using Chapter 3 The Picostat 39 40 eDAQ Potentiostats CHAPTER FOUR The QuadStat This chapter describes how to connect and use your QuadStat EA164 Note that when used with EChem software only a single QuadStat channel can be used With Scope software one or two channels can be used With Chart software one to four QuadStat channels can be used IMPORTANT Always make sure that the e corder is turned off before you connect or disconnect the QuadStat Failure to do this may result in damage to
73. he reference and working electrode lead wires which carry a high impedance signal are maintained at the same potential as the lead wire itself to minimise electrical interference and reduce lead capacitance The Potentiostat is powered by regulated 17 V 17 V and 8 V DC lines from the e corder see Figure 2 3 on page 9 The use of DC power allows its use inside Faraday cages 90 eDAQ Potentiostats Figure A 2 Block diagram of the Picostat Picostat The Picostat is designed to function in potentiostatic mode only that is it cannot be used as a galvanostat A block diagram of its construction is shown in Figure A 2 The Picostat is powered by regulated 17 V 17 V and 8 V DC lines from the e corder see Figure 3 3 on page 29 The use of DC power allows its use inside Faraday cages An error voltage is generated from the difference between the voltage on the Reference electrode and the excitation command voltage set by the e corder unit This difference or error voltage drives a high gain power amplifier VCVS voltage controlled voltage source the output of which is applied to the Auxiliary electrode in such a way as to minimise the error voltage The Picostat and the electrochemical cell to which it is connected forms a composite feedback control system in which the value of the Auxiliary potential is controlled in such a way as to make the Reference voltage equal to the desired Command voltage The current fl
74. he total charge transferred the total number of coulombs or electrons transferred is equal to the integrated current the settings used for chronoamperometry page 65 can also be used for chronocoulometry With Chart software it also necessary to set up an unused channel usually Channel 3 to be the integral of the current signal channel usually Channel 1 With an online function you need to actually be recording data to obtain the integral To configure Channel 3 you need to choose the Computed Input command from the Channel Function pop up menu which opens the Computed Input dialog box Figure 5 14 on a Windows computer and Figure 5 15 on a Macintosh For more information refer to the Computed Input section in the Chart Software Manual Post acquisition integration of a signal is also possible with the Chart Integral channel calculation which is accessed via the Integral Chapter 5 Techniques 75 Figure 5 14 Online integration of the current signal using Chart Computed Input integration Windows Figure 5 15 Online integration of the current signal using Chart Computed Input integration Macintosh Figure 5 16 Integration of the current signal using Scope Computed Functions Computed Input for Display Channel 1 Raw Data Input 1 qe Function Int Integral E 15 17 n 4 241 33 n s nid sl la EJ 100 m 2 gt Channel 1 v 3 El 0 3 a Turn Channel OFF
75. iR Compensation is adjusted until an appropriate amount of ringing is seen on the potential signal The maximum amount of iR compensation available depends on the selected gain range page 103 20 eDAQ Potentiostats Note that iR Compensation is set at the particular applied potential you have chosen If you then proceed to do an experiment involving a potential sweep the amount of compensation required for complete compensation will vary during the sweep and it is possible that the potentiostat will go into oscillation at some point To avoid this happening it is usual to always slightly undercompensate that is to find the point of ideal compensation and then to reduce the setting slightly The amount of undercompensation is usually determined by trial and error for a particular experiment Before using iR Compensation you should always consider other methods of reducing the uncompensated resistance For example could the reference electrode be more closely positioned to the working electrode perhaps by redesigning your reaction chamber or could the background electrolyte concentration be increased Also check to ensure that the reference electrode is not clogged or dried out It is always best to minimize cell resistance within the reaction chamber rather than trying to overcome the problem later with the potentiostat Applied potential Range 2y Level 0 0000 Y a Ds Set er ae as baseline Applied Potential
76. icostat to fail to work 32 eDAQ Potentiostats The Picostat uses two e corder input channels during normal operation The remainder of this chapter assumes that you have connected the current signal to e corder Input Channel 1 and the potential signal to e corder Input Channel 2 It is possible when using Chart or Scope software to connect the Picostat to other e corder input channels in which case the description that follows would change accordingly When using EChem software Channel 1 is always set to be the current signal the channel and Channel 2 is automatically set to be the potential signal the E channel Thus when using EChem software you must always connect the current signal Out to Input Channel 1 and the potential signal E Out to Input Channel 2 of the e corder Channel 2 normally displays the applied potential and its settings are controlled using the standard Input Amplifier dialog box described in the Chart and Scope Software Manuals which are installed as pdf files in the eDAQ Documentation folder on your computer hard disk First Use After you have installed the software connected the e corder and computer as described in the booklet that is supplied with the e corder system and connected the Picostat as described above you are ready to begin When the e corder is turned on and Chart software started the Picostat Online indicator green should light Touch the body of the Picostat or e co
77. ied potential with the slider bar or by entering the exact potential with the A button The resulting current signal should obey Ohm s law E R so that an applied potential of 1 V should produce a current of 10 pA while other potential settings should produce corresponding currents Potentiostat Control Window With Chart software the Potentiostat Control window is accessed from the Potentiostat command in the Channel Function pop up menu Figure 2 7 shows the control window on a Windows computer and Figure EEF Select Potentiostat in Turn Channel Off Channel popup menu Potentiostat Computed Input Units Conversion Pause resume scrolling Select input range Select low pass Windows A Potentiostat filter KA Potentiostat 1 Range Low pass j 1oomA 10k 0 02 m HABANA 5 Select Cell Mode i O Standby Potentiostat operating iS a amp has YF O Dummy O Galvanostat mode Real Oza Signal display area Ohigh z Select cell Mains filter C High Stability mode Invert Stabilization on ofl Mains filter Applied potential V iR Compensation on off Range 2y v t Level 0 000 oh Level 0 0000 Y a pad om Zero point calibrations Set applied potential as baseline Signal invert Applied potential controls iR Compensation controls 14 eDAQ Potentiostats Modes of Operation 2 8 on a Macintosh computer These windows control the variou
78. ignal connections from the terminal adaptor Black colored wires are connected to COM pins Figure 4 6 Using the external inputs of the QuadStat Note connection fo E In is only required for potentials of more than 2 5 V or for pulsed or ramped waveforms provide a second pathway to earth which could result in a ground loop which can actually increase signal interference The grounding connector is equivalent to the COM pins of the 20 pin terminal socket Figure 4 2 Channel 4 Channel 3 Channel 2 Channel 1 METRE EAE wOwO uw uw0 uwOwO uw w0 Pee To ecorder Input 8 7 6 5 4 3 2 1 For single channel operation use only Channel 1 For bipotentiostat operation use only Channel 1 and Channel 2 Channel 1 Single channel operation To e corder Input To e corder Output or waveform generator Channel 4 Channel 3 Channel 2 Channel 1 385 5 lt 5385 Out To e corder Input 8 7 6 5 To e corder Output or Multiple channel operation with the same waveform generator applied waveform on each channel Chapter 4 The QuadStat 47 Connecting the QuadStat Your QuadStat will have been supplied with an 2C cable DB 9 pin connectors at either end and nine cables with BNC connectors at one end and bare wires at the other First make sure that the e corder is turned off Then connect the 12C cable to the 12 connector
79. is remembered by the QuadStat and will be applied when you start a scan on Windows computers the set applied potential as baseine checkbox must also be ticked for this to happen Note that each QuadStat channel may have a different value for Eo This potential value will be summed with any external input waveform E n from the E In connection on the terminal strip connector on the QuadStat back panel The total potential Eyoja Eog Ein must be less than 10 V If you wish to use the QuadStat exclusively with an external voltage input for example with EChem software then make sure the Mapplied Potential checkbox is NOT ticked This will ensure that all Esg values are zero Offset Zero Offset El The current Offset control can be used to zero a background current signal so that small peaks or transient signals can be more accurately determined in the presence of a large baseline current signal First tick the Mors checkbox Then while the baseline current is being monitored click the L222 button It may take a few seconds to zero the signal Normally this will suffice to accurately zero the signal and you can then choose a more sensitive current range setting to observe Chapter 4 The QuadStat 57 Figure 4 12 The QuadStat Applied Potential controls with Chart software your signals Use the 4 buttons to manually adjust the amount of offset if required use Ctrl click for fine
80. lectrode connector as seen when looking at the front panel Working Electrode Shield Not connected Reference Electrode Reference Electrode Shield 6 eDAQ Potentiostats Table 2 1 Color coding on the leads of the electrode cable To ensure good grip the electrode cable alligator clips use a spring made from a good quality steel stainless steel is unsuitable for springs Avoid wetting of the alligator clips especially with electrolyte solutions which can hasten corrosion If the alligator clips are wetted then immediately disconnect from the Potentiostat rinse the clips with a little deionized water from a wash bottle to remove the electrolyte and immediately dry by patting with paper tissue The whole cable must then be allowed to dry thoroughly several hours at least before reuse Never immerse any part of the electrode cable in water or other liquid Color Electrode Yellow Reference Green Working Red Auxiliary coaxial shields which are maintained at the respective electrode potential Electrode Cable The Potentiostat is supplied with an electrode cable comprising three leads with each lead terminated by an alligator clip The Reference and Working electrode leads are shielded to protect the signals from external interference The alligator clips allow connection to a wide variety of electrodes and the leads are color coded to indicate the type of electrode to which they should
81. lip which allows connection to a wide variety of electrodes The leads are color coded to indicate the type of electrode to which they should be attached Table 4 1 The RE and WE leads are shielded to protect the signals from external interference The shields are driven to the same potential as the electrode to minimize lead capacitance If two electrode operation is required the auxiliary and reference electrode leads red and yellow can be attached to the single counter electrode A2 eDAQ Potentiostats Table 4 1 Color coding on the leads of the electrode cables Color Electrode Yellow Reference Green Working Red Auxiliary The Online Indicators Along the lower edge of the QuadStat front panel are a series Online indicators Figure 4 1 When lit they indicate that the software such as EChem Chart or Scope has located and initialised that QuadStat channel If the light does not go on when the software is run check that the QuadStat is properly connected If there is still a problem please refer to Appendix B Troubleshooting page 95 The Overload Indicators Also along the lower edge of the front panel are the Overload indicators Figure 4 1 When lit these indicates that the QuadStat has overloaded which usually occurs because it has gone out of compliance because of an open circuit such as an unconnected or faulty electrode or the resistance is too high in the electrochemical ce
82. ll High resistances can be often be encountered when electrodes are fouled by the products of electrolysis reactions The QuadStat tries to compensate by increasing the compliance potential that is the potential between the auxiliary and working electrodes If the compliance voltage exceeds specification about 11 V potential control of the cell is lost and drifting or oscillation of the signal can be seen Any data collected during this period is unreliable and should be discarded The QuadStat Overload indicators will remain lit once an overload has occurred they will be reset once the scan has finished If an overload indicator comes on repeatedly and your connections are good then try bringing your electrodes closer together and or increasing electrolyte concentration and or modifying your Chapter 4 The QuadStat 43 Figure 4 2 The QuadStat back panel Figure 4 3 The 20 pin screw terminal adaptor experimental conditions to avoid fouling of the electrodes Redesigning your electrochemical cell may be necessary Normally electrochemical cells are designed to keep the reference and working electrodes very close together however when a potential overload occurs you also need to consider the distance between the auxiliary and working electrodes 4 mm socket ground connection Made in Australia by eDAQ Pty Ltd C No user serviceable parts inside Refer servicing to qualified service personn
83. lot the current signal usually on Channel 1 versus Channel 3 and a near straight line should be obtained with a slope of a Figure 5 11 With the Curve Fit extension installed you can use the Curve Fitting command Windows menu to fit your current signal data with an Chapter 5 Techniques 71 idealised curve The Curve Fit analysis extension and accompanying documentation can be downloaded free from the eDAQ web site www eDAQ com The extension file should be put into the Chart Extensions folder inside the Chart folder on your hard disk It is unlikely that the current signal will decay to exactly zero due to convection currents in the vessel causing non ideal diffusion so a small non zero constant b is added Also the equation is very sensitive to the exact instant when fis zero which is a problem if you have selected data very close to zero time in the Curve Fitting window it is usually best to use the t O at start of block option as shown in Figure 5 12 In this case to get a well behaved equation when the data selected start at very close to zero time initially add a small time correction c This allows for the errors in the estimation of time zero and the fact that the Potentiostat has a finite bandwidth and so the current signal will take a small amount of time to register a true value after a sudden change in potential Thus a better form of the equation to be fitted is j 4b Jt e This
84. ls to enter a numerical value When using Chart software on a Windows computer the default potential will be the same as the Baseline value in the Stimulator control Excitation Range Excitation Range p When using Chart software on a Windows computer you have the option of limiting the range over which the applied potential can be set Smaller ranges offer finer control with the slider bar or text entry of the applied potential On a Macintosh computer use the range control in the Stimulator Constant Output dialog box Figure 5 8 Remem ber Potentia M Set applied potential as baseline when dialog is closed When using Chart software on a Windows computer you can select the checkbox labelled Set applied potential as baseline This causes the potential set with the slider bar or text entry to be transferred to the Stimulator baseline control when the window is closed 38 eDAQ Potentiostats Maintenance Your Picostat will not require maintenance during daily operation However you should periodically check the Picostat for optimum results First set up the Picostat and e corder as outlined earlier in this Chapter Disconnect the electrode cable from the Picostat Open the Picostat Control window Figure 3 7 or Figure 3 8 Adjust the current range to 10 pA the Low Pass filter to 10 Hz and select Real mode After a couple of seconds the resulting current signal should have stabilised and be close to zero If t
85. lso has the ability to zero or offset a background current signal which can be of use when trying to amplify small peaks on a large background signal see Zero Offset page 57 The Chart software Multiple Point Calibration extension can be used to extend the useful range of metabolite concentrations over which this sensor can be used by compensating for non linear signal response Dissolved Oxygen dO Sensors Usually a polarographic Clark oxygen sensor electrode and meter are purchased from the same manufacturer to ensure matching sensitivity However depending on the current requirements of your oxygen sensor the Potentiostat QuadStat or Picostat may be a suitable alternative to a standard meter as they have adjustable sensitivity and can be matched to a wide range of current signal requirements In addition you can use them to alter the polarising voltage to fine tune your sensor Most polarographic oxygen electrodes comprise a gold or platinum cathodic working electrode to which the working electrode lead is attached and a silver anodic counter electrode to which the reference and auxiliary electrode leads are attached Usually a reducing 86 eDAQ Potentiostats polarising voltage applied potential of between 0 7 to 0 8 V is required at the working electrode to effect the reaction O 4H 4e gt 2H O The exact potential can be varied to suit the sample being measured and to minimise side reactions A
86. lter Cancel Drag ticks and Axis expansion Select cell Invert signal labels to adjust axis contraction mode should produce corresponding currents If this is so then your QuadStat is working correctly and you can proceed to your experiment QuadStat Control Window With Chart software the QuadStat Control window is accessed from the QuadStat command in the Channel Function pop up menu Figure 4 9 shows the control window on a Windows computer and Figure 4 10 on a Macintosh computer These windows control the various current ranges and filtering options for the QuadStat With Scope software the corresponding controls are shown in Figure 4 11 54 eDAQ Potentiostats Signal Display The current signal is previewed scrolling across the display area Note that the signal is not being recorded to hard disk at this stage and that when the window is closed the signal trace is lost You can stop start the signal scrolling by clicking the Pause Resume button f4 You can shift or stretch the vertical Amplitude axis to make the best use of the available display area All changes to axis scaling are reflected in the Chart and Scope main window and vice versa Range Setting the Range a The Range pop up menu lets you select the input current range or sensitivity The QuadStat has ranges of 2 nA to 1 mA You should set the range so that it is larger than the biggest current that you expect to encounter during
87. must be entered as a New Equation in the Curve Fit extension the very first time you use it Figure 5 12 Because of the discontinuity that occurs when the denominator is zero first try fixing c to a small positive value and iterating for better values of a and b Some trial and error will be involved while you make guesses that are suitable for the initial values to iterate After the better estimates for a and b have been determined and iterated c can be unlocked so that it refines during the next iteration Figure 5 12 Your data selection should not include points very close to zero time the Potentiostat will require some time to settle nor points taken at very long times when convection aided diffusion will produce non ideal behaviour The exact time period that is suitable will depend on the size of the electrode and some trial and error to determine the time interval to give best results will probably be required After the file is saved the Curve Fit Cottrell equation will be available whenever you open Chart data file on the same computer or even when you transfer the data file to another computer on which Chart software 72 eDAQ Potentiostats Figure 5 12 Fitting a Cottrell equation to data with the Curve Fit extension At the time of writing the Curve Fit extension is only available for Chart for Macintosh Edit Function Name Cottrell F tj ae b 00 aloja Variable 8 sec
88. necessary Normally cells are designed to keep the reference and working electrodes very close together however when a potential overload occurs you also need to consider the distance between the auxiliary and working electrodes Note that a potential overload is quite different from a current overload condition A current overload is caused when the current signal eDAQ Potentiostats Figure 2 3 The Potentiostat back panel Figure 2 4 The pin assignments for the C DB 9 connectors BNC output BNC input connectors connector E Out 1 Out Eln 4 mm socket ground connection DB 9 pin 12C connectors 12 control signals Power lines 12 control signals Q Q Q 508 AVS o gt gt 2 So 58 PAGD 7 3 a7 BB BO OBB SB 2005 3303 OXUO2223 2 22 2hOxa E DDD OD nD D DM N N mn 02 ZERA LLLA agezgeZaBaz lolo oloj oS 50lolololo 6 0 0 O 09 90 O O O nput Output A exceeds the full scale limits of the range setting of the current channel and is usually caused by a low resistance between the electrodes The Back Panel The back panel of the Potentiostat is shown in Figure 2 3 E Out Out and E In Connectors The Potentiostat back panel has three BNC connectors labelled E Out Out and E In The E In is connected to the Output o
89. nt If during the experiment the current signal exceeds the range then the signal will go off scale and be lost Low pass Filtering ome Y The Potentiostat incorporates four low pass filters at 10 kHz 1 kHz 100 Hz and 10 Hz for removal of high frequency signals noise In addition the e corder provides filter settings at 1 2 5 20 50 200 500 and 2000 Hz Chart software on Windows computers As a general rule the 10 Hz filter setting is highly effective for the removal of mains hum 50 or 60 Hz interference and should be employed whenever possible However it should not be used for pulsed amperometric or voltammetric experiments where the pulses are shorter than 100 ms or for experiments where rapid scan rates greater than about 100 mV s are used With Chart and Scope software there is an additional Mains Filter checkbox Fimainsfiter If this is ticked then the e corder will apply a mains filtering algorithm to the incoming signal which removes repetitive signals occurring at 50 or 60 Hz which are typical of mains interference Note that the mains filter is not a notch filter and that it can remove a 50 or 60 Hz interference even if it is not a pure sinusoidal function However the mains filter does take a few seconds to learn the pattern of the interference so that you will need to record for longer than this for it to take full effect The mains filter can be employed even for experiments in which ther
90. ntial applied to the electrodes while the Potentiostat control window is open When you close the control dialog using EChem or Scope software the Potentiostat will revert to Standby mode until the Start button is clicked to begin a scan If you are using Chart software the Potentiostat will remain in Real mode when the dialog is closed so that when you start and stop recording data the electrodes will remain active This allows periodic recording of the signal from for example amperometric biosensors without disturbing the environment around the electrodes High Stability Operation Drs If the High Stability box is ticked then extra capacitance is introduced into the Potentiostat control loop This stabilizes the Potentiostat in 18 eDAQ Potentiostats situations where oscillation is encountered for example where large surface area electrodes are being used in highly resistive solutions Do NOT use High Stability when in Potentiostat mode unless you first encounter stability problems High Stability decreases the bandwidth of the of the Potentiostat control loop Thus High Stability mode should never be used when fast sweep rates gt 1 V s or when short term pulses lt 0 1 s are employed as it will produce a noticeable phase lag between the desired and actual applied potential Also High Stability operation should not be used to try to correct for oscillations introduced by excessive iR compensation High Stability
91. oad indicators to light The Back Panel The back panel of the QuadStat is shown in Figure 4 2 E Out Out and E In Connectors The QuadStat is supplied with a 20 pin screw terminal adaptor Figure 4 3 which plugs into the 20 pin socket on the back panel The pin positions are labelled Out E Out E In and COM for each QuadStat channel Channels 1 4 The COM common pins are provided for connection to signal ground black wires of the supplied coaxial cables Figure 4 5 You can use any COM pin for the ground connection of any Out E Out or E In signal 12 control signals Power lines I2C control signals Q Q AUVs AVS gt 20 gt gt A gt EAR g TN N o E woe 12 ZT B33 30 OBBB 222 5 Z U U axvunalae ee SOPA D005 D DODO N 192 102 N ZABASELLA eL 598Z Em O O O O O O O O os SEY Input Output Chapter 4 The QuadStat 45 12C Connectors The QuadStat back panel Figure 4 2 has two DB 9 pin I2C bus connectors labelled Input and Output The Input connector provides power to the QuadStat and carries the various control signals for gain range and filter selection to and from the e corder connection A cable is provided with the QuadStat for this purpose The pin assignments are shown in Figure 4 4 The Output connector can be used for the attachment of ano
92. oftware Installer CD In many cases a problem can be fixed by turning the e corder and computer off checking connections and starting again Also try performing the maintenance checks on page 22 page 39 and page 59 If you cannot correct the problem then please contact your eDAQ representative The On line indicator fails to light when the software is opened e Check that the e corder is connected to the mains power and that it is turned on e Check that Potentiostat Picostat or QuadStat is properly connected to the e corder and that the cables are not loose Especially check that the E in Out and E Out cables are correctly connected see page 11 page 31 and page 48 e If possible change cables and try again If a second cable works and you find that the first cable is faulty you should contact eDAQ for a replacement e If you are using EChem software check that the E In cable is connected to the e corder output and the I Out and E Our cables are connected to e corder Input 1 and 2 see page 11 page 31 and page 47 eDAQ Potentiostats 95 e Try using the Potentiostat Picostat or Quadstat with another e corder if available If the Online indicator fails to light on the second e corder the Potentiostat Picostat or Quadstat may be faulty contact eDAQ If it works correctly on a second e corder then the first e corder may be faulty contact eDAQ The Potentiostat
93. ol Port I2C input and output Power requirements Physical Configuratio Male and female DB 9 pin connectors Provides control and power to the Potentiostat 17 VDC 8 VDC 25 mA typical 2W n Dimensions h xw xd 50x 76 x 260 mm 1 96 x 3 0 x 10 2 inches Weight 0 8 kg 1 8 lb Operating conditions 0 35 C O 90 humidity non condensing eDAQ reserves the right to alter these specifications at any time Appendix C Specifications 103 Picostat Electrometer amp Power Amp Compliance voltage Maximum control voltage Output current Input impedance Input bias current gt 13V 10 V 100 nA maximum 1013 Q 1 pF lt 250 fA O 25 C 60 fA typical Current Measurement and Control Current ranges Gain DC current error Filter setting e corder filter settings Bandwidth unfiltered Drift with temperature Control Port I2C input and output Power requirements 100 50 20 10 5 2 1 nA 500 50 20 10 pA 10 1 0 1 nA V lt 1 FS on ranges of 10 pA 1 nA lt 0 5 FS on ranges of 2 100 nA 10 Hz low pass 3rd order Bessel 10 kHz to 1 Hz in 10 5 2 steps gt 10 kHz on ranges of 20 100 nA 1 kHz on ranges of 10 pA 10 nA lt 20 pV C Male and female DB 9 pin connectors Provides control and power to the Picostat 17 VDC 20 mA 8 V DC 20 mA 1 W quiescent 104 eDAQ Potentiostats Physical Configura
94. operation can be used routinely when performing fixed potential experiments with amperometric sensors where the response time of the sensor is relatively slow gt 0 01 s It is likely you will need to use High Stability mode when in Galvanostat mode especially with highly resistive loads Note that High Stability operation is not required for either ZRA or High Z operational modes because the Potentiostat control loop is disabled Current Signal Zero Point Calibration The Calibrate button is available in Potentiostat and ZRA operating modes page 15 When the Calibrate button is clicked it corrects for any internal offset error on the current signal This is only required for very accurate determination of signal values Current accuracy will be improved from about 1 of full scale of range to better than 0 2 If you do not need this accuracy then you do not need to use the Calibrate button For best results allow about 10 minutes after opening powering up the e corder before using the Calibrate function This allows the unit to warm up ambient temperature variation of more than a few degrees during an experiment may require periodic recalibration to maintain maximum accuracy When calibrating in ZRA mode you must first remove the Electrode connector from the Potentiostat Chapter 2 The Potentiostat 19 When in Potentiostat mode clicking the Calibrate button will zero the current signal using the Dummy cell in
95. or electrosynthesis The production of organic compounds in highly resistive non aqueous solvents often requires the addition of large amounts of electrolyte to sustain the current flow and which can lead to difficulties in later separation of the product For studies using water or other protic solvent the addition of a small quantity of acid or base can greatly increase the conductivity of the solution without having to add large amounts of electrolyte Controlled Current Electrolysis These techniques are essentially the same as Chronopotentiometry page 77 and require the use of a galvanostat The Potentiostat when Chapter 5 Techniques 83 operated in Galvanostat mode is suitable for experiments where currents less than 100 mA and potentials less than 10 V are anticipated Please note that the Picostat or QuadStat cannot be operated as a galvanostat A constant current is applied between the working and auxiliary electrodes and the potential at the working electrode is monitored as the substrate is oxidized or reduced As the electrolysis continues the substrate is eventually completely consumed and the potential will alter as the galvanostat tries to maintain a constant current Both the potential and the current flow can be monitored with Chart software The integrated current that is the total charge transferred can also be determined which can be used to determine the extent of reaction Electrosynthesis an
96. otential A ppl ied Potential IV Mains Filter Set mains Fo Invert filter Cancel Drag ticks and Axis expansion Select cell Invert signal labels to adjust axis contraction mode You can stop start the signal scrolling by clicking the Pause Resume button f4 You can shift or stretch the vertical Amplitude axis to make the best use of the available display area All changes to axis scaling are reflected in the Chart and Scope main window and vice versa Setting the Range es The Range pop up menu lets you select the input current range or sensitivity The Picostat has ranges of 10 pA to 100 nA if you require a system to monitor larger currents the Potentiostat has ranges of 20 nA to 100 mA You should set the range so that it is larger than the biggest current that you expect to encounter during your experiment If during the experiment the current signal exceeds the range then the data will be truncated and therefore lost 36 eDAQ Potentiostats Low Pass Filtering M Mains Filter The Picostat has an internal 10 Hz low pass filter for removal of high frequency signals noise The Off setting gives the full bandwidth of the Picostat which can be up to 16 kHz but which may also be limited by the characteristics of your electrodes and sample solution The 10 Hz filter setting is highly effective for the removal of mains hum 50 or 60 Hz interference and as a general rule sho
97. ou are still experiencing difficulties with your experiments then check the electrodes reference electrodes in particular tend to become clogged or dry out with age and the design and condition of the reaction vessel and any salt bridges that you are using Chapter 2 The Potentiostat 23 24 eDAQ Potentiostats A TAR jee The Picostat This chapter describes how to connect and use your Picostat EA162 IMPORTANT Always make sure that the e corder is turned off before you connect or disconnect the Picostat Failure to do this may result in damage to the e corder and or the Picostat IMPORTANT The Picostat is a highly sensitive current measuring device To prevent damage by static discharge always make sure you are earthed before touching the Picostat electrode connector connecting the lead wires or before you connect the lead wire alligator clips to the electrodes You can do this after first connecting the Picostat and e corder by touching the outer casing of the e corder or Picostat This will connect you to earth via the electrical grounding of the instrument and any static charge you have collected will be dissipated eDAQ Potentiostats 25 Figure 3 1 The Picostat front panel Figure 3 2 The Picostat Electrode connector as seen when looking at the front panel The Front Panel The front panel of the Picostat is shown in Figure 3 1 Electrode Connector
98. our computer hard disk First Use After you have installed the software connected the e corder and computer as described with the booklet supplied with the e corder system and connected the Potentiostat as described above you are ready to begin When the e corder is turned on and Chart software started the Potentiostat Online indicator green should light From the Channel 1 Function pop up menu select the Potentiostat command which opens the Potentiostat Control window Figure 2 7 Windows or Figure 2 8 Macintosh This window allows you to preview the current signal without actually recording the signal to your computer s hard disk If the menu says Input Amplifier instead of Potentiostat then the software has not recognised the Potentiostat Exit the software check all your connections and try again By default the control window opens with the Potentiostat in Standby mode that is with the reference and working electrodes isolated so that Chapter 2 The Potentiostat 13 Figure 2 7 Potentiostat controls with Chart software no current will flow through your electrodes To connect to the Potentiostat lead wires you must select Real mode When you click Cancel or OK the Potentiostat will revert to Standby mode until recording is started Now select Dummy mode operation You will need to adjust the gain range to 20 pA to accommodate your signal amplitude You can now adjust the appl
99. ow in the Working electrode is the quantity being measured Overload Front Panel Detector Back Panel Overload Operate Power Amp Subtractor E In d Comman ji Auxiliary O F Gain O voltage 5 Error lt Voltage fa 3 Ref Amp E Out a i Reference Reference O o Hi O voltage Shield OH Operate Low pass Filter O Out Virtual Ground O V Working OH to V 2C Input Shield O 2C Control Interface 7 Online C Output Appendix A Technical Aspects 9 When the Picostat is in Standby mode the Working and Reference electrodes are disconnected by an internal relay This prevents unwanted current flowing through your electrochemical cell An overload condition is indicated when the error voltage exceeds a small non zero value This indicates that the system could not establish or sustain a balanced state The Overload light will be reset when scanning is stopped or when the Picostat controls are next accessed The reference voltage is measured by a high input impedance amplifier which provides a low impedance output to the e corder unit The voltage at the working electrode is effectively held at a virtual ground potential zero volts by a voltage to current convertor the output of which reads directly in current units and is also applied to the e corder unit The Picostat has three gain ranges of 100 pA V
100. p Compliance voltage gt 10 V Output current 100 mA maximum Current limit 200 mA Slew rate 3 V ps Electrometer Input resistance 1013 Q Input bias current lt 1 pA 25 C Input voltage 10 V maximum Output voltage 10 V maximum Output offset voltage 0 8 V maximum Output offset drift 0 8 pV C Gain accuracy 0 1 eDAQ Potentiostats 101 Current Measurement and Control Potentiostat gain pA V Current Range Setting 100 50 20 mA 10 5 2 mA 1 000 1 mA 500 200 pA 100 100 50 20 pA 10 10 5 2 pA 1 1 pA 500 200 nA 0 1 100 50 20 nA 0 01 Maximum current signal Low pass filters e corder filter settings Gain accuracy Drift with temperature Control Loop Voltage offset error Voltage gain error Bandwidth unity loop gain Ramp follower error 10 Y 10 000 1000 100 10 Hz 3rd order Bessel 10 kHz to 1 Hz in 10 5 2 steps 0 2 at ranges 1 mA or smaller 1 at ranges 10 mA or larger 0 3 mV C mV 0 1 16 kHz O 90 lag 160 Hz high stability mode 90 lag 1 mV 100 V s 1 mV 1 V s high stability mode 102 eDAQ Potentiostats iR Compensation Current Range Setting Compensation Range 100 50 20 mA 0 100 10 5 2 mA 0 1000 1 mA 500 200 pA 0 1kO 100 50 20 pA 0 10kO 10 5 2 pA 0 100 ko 1 pA 500 200 nA 0 1MO 100 50 20 nA 0 10 MO Contr
101. p Functions lt lt f Coefficients 3 1 Define the Cottrell O Curve Fitting i Cottrell curve fitting of chronoamperometric data 3 67386 28994 4 0 38392 Coefficients Error ma 6 000 sb 0 500 fac 0 010 Channel 1V relationship as a new equation First lock in a value for c then try guesses for a and b until an approximate fit is obtained ia gt Seleot Fit El Tie Cottrell F Q za sqrt t o Guess __Fit_ o Curve Fitting SE SSE 6244 232_RE 0 66937 _ Z Cottrell curve fitting of chronoamperometric data t 3 3445 Real 4 0964 Fit 3 79451 4 0 30188 ICoefficients HError Wa 4 000 0 010 Set Scale ib 1 610 0 005 Auto Scale jac 0 010 1 Fitting complete in 2 Usually use t O _FullRange iterations qe t 0 at start of selection at start of block v tzoat start of block Channel 1 3 Channal gt 3 E 2 5 ia gt k Select Fit men Cottrell F a sqrt t e b y 3 SSE 1518 678 _R 0 91959 Guess ht Curve Fitting B Cottrell curve fitting of chroncamperometric data t 7 693s Real 3 08089 Fit 3 01339 4 0 06749 Coefficients Error ia 7 998 ib 0 301 mc 0 999 0 005 0 002 0 002 lterate by clicking the Fit button refining a and b only If the initial guesses
102. provided they adhere to this agreement Each separate purchase of the eDAQ software licenses it to be used on two computers at any given time on one computer for data acquisition with a e corder hardware unit and on a second computer for the analysis of existing data files Although multiple eDAQ Potentiostats 117 copies of a program may exist on several computers more than two copies must not be used simultaneously Departmental company licences are available if you wish fo run more than two copies simultaneously Technical Support Please register your unit to receive technical support Technical assistance is available via email Please describe the problem with as much detail as possible Include a small example data file if appropriate Please also state e the model and serial number of your e corder unit and Potentiostat or Picostat e the type of computer and operating system being used for example Windows XP or Macintosh OS 10 2 e the software version you are using for example Chart v5 1 2 We endeavor to answer all your questions but in some cases for example where the problem relates to the other equipment that you are using a nominal fee may be charged Jurisdiction eDAQ Pty Ltd is bound by the laws of New South Wales in Australia and any proceedings shall be heard by the Supreme Court of New South Wales in Australia Disclaimer eDAQ reserves the right to alter specifications of hardware
103. r and it can remove 50 or 60 Hz interference even if it is not a pure sinusoidal waveform However the mains filter does take a few seconds to learn the pattern of the interference so that you will need to record for longer than this for it to take full effect The mains filter can even be employed for experiments in which there are sudden potential jumps Inverting the Signal Om The Invert checkbox allows you to invert the incoming current signal It provides a simple way to redefine the directions up or down of an anodic or cathodic current signal This control does not affect the direction of current flow at the electrodes O Standby Cell Control coun Real The QuadStat can be in one of three operating modes controlled by the Cell radio buttons e Standby If Standby mode is selected the auxiliary and reference electrodes are isolated by an internal relay which effectively means that all the electrodes are at a floating potential and that no current will be passed through your experimental solution The electrodes will not be connected until the QuadStat control dialog is closed and the Chart Scope or EChem Start button is clicked to begin a scan The Applied Potential control is disabled in this mode e Dummy When Dummy mode is selected the QuadStat channel is connected to the internal 1 MQ dummy cell You can then use the Applied Potential slider control to vary the voltage applied to the dummy cell The QuadSt
104. rder to discharge any static charge that you may have accumulated then attach the 100 MA test resistor supplied with the Picostat to the electrode leads so that the Working electrode lead is connected to one end of the resistor and Reference and Auxiliary electrode leads to the other From the Channel 1 Function pop up menu select the Picostat command which accesses the Picostat control window Figure 3 7 Figure 3 8 or Figure 3 9 The Picostat control window allows you to preview the current signal without actually recording the signal to the computer hard disk If the menu says Input Amplifier instead of Picostat then the software has Chapter 3 The Picostat 33 Figure 3 7 Accessing the Picostat controls with Chart software Windows Figure 3 8 Accessing the Picostat controls with Chart software Macintosh display area Turn Channel Off Pico u Computed Input Units Conversion Picostat v No Calculation Current signal Drag ticks and labels to adjust axis scaling Start stop scrolling Select input range Select low pass filter Arithmetic S Cycle Variables Det mains Differential filter Digital Filtering Invert signal Integral Shift Select Real gothig or Standby Select Picostat from mode the Channel bate runction pop up menu Excitation Range Applied
105. re connected is able to correctly indicate an overload When you use a common reference and auxiliary electrode with multiple working electrodes AND use an external waveform at E In on Channel 1 then this waveform will be effectively applied to all working working electrodes whether or not the separate E In connectors are linked together as shown Figure 4 6 Thus it is recommended to use the connections shown in Figure 4 6 so that the signals seen at E Out on each channel will be correct For example if a triangular waveform is applied at QuadStat Channel 1 then all the QuadStat channels will perform cyclic voltammetry The triangular potential waveform can be offset at each separate working electrode by using the Applied Potential control page 57 Finally when you use a common reference and auxiliary electrode with multiple working electrodes make sure that all the QuadStat channels are set to the same cell mode Standby Dummy or Real page 56 Recording signals with some channels set on Dummy while others are on Real Standby can cause incorrect current signals Using Multiple References and Auxiliaries The QuadStat can also be used to conduct experiments in different reaction vessels In this case you should use a set of three electrodes working reference auxiliary in each reaction vessel Each QuadStat channel behaves as a separate potentiostat Independent signals can be applied at each QuadStat channel E in connector if desi
106. red so that different experiments can be run in each reaction vessel Please note that the use of multiple reference and auxiliary electrodes in the same reaction vessel will almost certainly lead to unpredictable effects and is not recommended Chapter 4 The QuadStat 5 First Use After you have installed the software connected the e corder and computer and connected the QuadStat as described above you are ready to begin When the e corder is turned on and Chart software started the QuadStat Online indicators green Figure 4 1 on page 42 should light for every channel connected From the Chart software Channel 1 pop up menu select the QuadStat command also on Chart software Channels 3 5 7 if all four working electrodes are being used which accesses the QuadStat control window Figure 4 9 Figure 4 10 or Figure 4 11 The QuadStat control window allows you to preview the current signal without actually recording the signal to the computer hard disk If the menu says Input Amplifier instead of QuadStat then the software has not recognised the QuadStat Exit the software check all your connections and try again By default the control window opens with the QuadStat in Standby mode that is with the reference and working electrodes isolated so that no current will flow through your electrodes To connect to the QuadStat electrode lead wires you must select Real mode When you click Cancel or
107. rence electrode to measure the potential difference between the leads The high impedance potential signal is delivered at Out The auxiliary lead red can be connected to a third electrode or test point to provide a ZRA current signal at E Out Figure 2 3 Please make sure the electrode lead wires are connected appropriately to your experiment before operating in any of these modes In particular incorrect placement of leads may damage the reference electrode if one is being used Signal Display The current signal is previewed in the scrolling display area Note that the signal is not being recorded to hard disk at this stage and that when the window is closed the signal trace will be lost By using the Dummy or Real modes you can investigate the effect of the Applied Potential page 21 on the current signal You can stop start the signal scrolling by clicking the Pause Resume button uJ eDAQ Potentiostats You can shift or stretch the vertical Amplitude axis to make the best use of the available display area similar to the amplitude axis in the main Chart Scope or EChem window Range Setting the Range lom Use the Range pop up menu to select the input current range channel sensitivity The Potentiostat has ranges of 100 mA to 2 nA while resolution within each range is 16 bits or 0 0015 You should set the range so that it is larger than the biggest current that you expect to encounter during your experime
108. s current ranges and filtering options for the Potentiostat Mode Potentiostat O Galvanostat ORA OHighz The EA161 Potentiostat can be operated in several different modes by selecting the appropriate radio button e Potentiostat Chart Scope or EChem software described below For three electrode use connect the working green reference and auxiliary red leads appropriate electrodes or circuit test points The current signal is provided at Out Figure 2 3 The potential signal is provided at E Out When two electrode potentiostat Select Potentiostat in the Figure 2 8 Channel pop up menu Potenti ls with 2 otentiostat controls wit Tun ChanneROr Chart software Potentiostat Macintosh Computed Input Drag ticks and Select cell Select input Select low Units Conversion labels to adjust axis mode range pass filter t Na Calrulatinn Potentiostat O Input 1 Poj ntiostat 0 029 mA Range 100 mA 3 m i z a04 Low Pass 10 kHz E Select oe O Standby 9 Potentiostat operating C2 a TS UT A Dummy O Galvanostat _ d FETE i LS mode o Signal display are Real ZEN J E O Hi E A O High Stability High Z ive Applied Potential V am arene L 9 Set applied A 80 cit pe potential u a a M iR Compensation Q Test Set iR z compen 0 O y A Y sation 0 10 Mains filter Mains Filter M invert on off Units Cancel Cox gt
109. s on a large background signal see Zero Offset page 57 88 eDAQ Potentiostats APPENDIX A Technical Aspects This appendix describes various technical aspects of potentiostat construction however you do not need to understand this material to use the Potentiostat Picostat or QuadStat Please note that this information is not intended as a service manual and that user modification of the equipment voids your rights under warranty The Potentiostat Picostat QuadStat and other eDAQ Amps have been designed to be used with an e corder system All internal functions gain ranges filters real standby dummy cell selection of the Potentiostat Picostat or QuadStat are controlled from the e corder by sending information on a special communications connection called the 112C bus which also supplies DC power Potentiostat The Potentiostat is designed to function as a e potentiostat Chart Scope or EChem software e galvanostat Chart or Scope software e ZRA zero resistance ammeter Chart or Scope software or e high impedance voltmeter Chart or Scope software The mode of operation is under software control A block diagram of the Potentiostat circuitry is shown in Figure A 1 eDAQ Potentiostats 89 Figure A 1 Block diagram of the Potentiostat
110. s page 83 monitor the potential signal when the Potentiostat is used as a galvanostat to maintain a constant current at the working electrode Note that the Picostat and QuadStat cannot be used as galvanostats e Monitoring of amperometric sensors page 84 including dissolved oxygen and nitric oxide electrodes e zero resistance ammeter or high impedance voltmeter with the Potentiostat page 15 62 eDAQ Potentiostats Linear Scan Techniques Linear sweep or cyclic voltammetry are usually best performed with EChem software However Scope also incorporates Stimulator and Output Voltage commands which can be used to control the analog output of the e corder to create a waveform suitable for these techniques albeit less conveniently than with the EChem software With Scope software up to 2560 points can be collected on one channel at a rate of up to up to 100 kHz on both channels Fast Cyclic Voltammetry Scope software has a number of features that can perform Fast Cyclic Voltammetry FCV These are accessed via the Stimulator and Output Voltage commands in the Setup menu Figure 5 1 The base potential is set by using the Stimulator Constant Output dialog box while the waveform is generated using the Stimulator Up amp Down Figure 5 2 or Triangle Figure 5 3 waveforms See the Scope Software Manual for further details In Figure 5 2 the base potential has been set to 1 00 V and a potential ramp has
111. s working correctly but you are still experiencing difficulties with your experiments then you should now check the electrodes you are using the connections to them and the design and condition of the reaction vessel and any salt bridges that you are using Chapter 4 The QuadStat 59 60 eDAQ Potentiostats Ga ALP ive Rk FIVE Techniques The Chart and Scope software supplied with your e corder can be used to perform many different electrochemical techniques This chapter provides an overview of these techniques but you will need to also refer to the Chart Software Manual and Scope Software Manual which are installed as pdf files in the eDAQ Documentation folder on your computer hard disk Also discussed is the use of the Potentiostat when configured as a galvanostat Additional experiments such as current sampled staircase linear sweep differential pulse normal pulse square wave and staircase cyclic voltammetry and pulse amperometry can be performed with the optional EChem software see the EChem Software Manual or contact eDAQ for more details eDAQ Potentiostats 6l NOTE The QuadStat also has internal potential adjustment of 2 V When the e corder output is connected to a QuadStat channel E in this value is summed with the value set by the Chart or Scope Stimulator controls to a maximum of 10 V Introduction The Potentiostat Picostat and
112. sing voltage is the potential at which the Potentiostat Picostat or QuadStat applies at the working electrode Note that the QuadStat can be employed with up to four sensors each at a different potential all using the same reference and auxiliary electrode The QuadStat also has the ability to zero or offset a background current signal which can be of use when trying to amplify small peaks on a large background signal see Zero Offset page 57 Normally Chart software rather than Scope is the better choice of recording software for these types of sensor The Units Conversion feature of Chart can be used to perform two point calibration of the signal in the units of your choice which is satisfactory for most uses see the Chart Software Manual for more information If multiple point or non linear calibration is required then the Chart Multiple Point Calibration extension can be used with up to twelve calibration points If you are performing a flow injection analysis or similar experiment then the Chart Flow Analysis extension available on Windows computers only can be used to determine peak areas prepare a calibration graph and apply the calibration results to determine the amount of material in the unknown sample peaks PowerChrom software can also be used with the QuadStat and e corder hardware as a electrochemical detector for HPLC experiments You can download the extensions and accompanying documentation from the
113. t occurred 96 eDAQ Potentiostats The results show peaks or steps at the inverse polarity expect to see i e a peak may be occurring at 0 5 V when it should be at 0 5 V e Check that you are connected to the correct Output or of the e corder See Connecting the Potentiostat page 11 or Connecting the Picostat page 31 or Connecting the QuadStat page 48 e If you are using Chart or Scope software check that the Invert box is checked or not as appropriate for the potential recording channel The results show peaks or steps at different potentials than you expect e See previous section e Make sure the reference electrode is connected to the correct yellow lead wire page 7 page 27or page 43 Connection of the reference electrode to either the working or auxiliary leads can also cause rapid electrode deterioration requiring electrode replacement e Check the condition of the reference electrode All reference electrodes age For example and Ag AgCl electrode will age with exposure to light Eventually the white light grey coating of AgCl on the central silver wire will be replaced by a brown black coating of silver oxide As this process takes place the apparent positions of your voltammetric peaks will appear to shift to different potentials Most Ag AgCl electrodes can be quickly regenerated by placing the silver wire in 1 M hydrochloric acid solution for a minute or two any silver oxide is quickly recon
114. t signal The real time methods will give good results only if the appropriate sensitivity range has been pre selected and it is not always possible to determine this beforehand A good strategy is often to use the real time integral function to get an idea of what is happening during an experiment and the use post acquisition integration to prepare data for a final report With Scope software the current signal can be integrated by using the Computed Functions command Figure 5 16 The Integrate item is chosen from the Function menu This is actually a post acquisition function you can always cancel it afterwards to look at the underlying current data Refer to the Scope Software Manual for more information Chronopotentiometry Chronopotentiometry requires that a constant current be maintained between the working and auxiliary counter electrodes The potential at the working electrode is monitored For many systems the potential will remain approximately constant until the electroactive species is consumed after which there will be a sudden change in the potential For this type of experiment it will be necessary to run the Potentiostat in Galvanostat mode with Chart or Scope software For correct operation make sure that the CH 1 1 cable of the Potentiostat is connected to Input 1 of the e corder and the CH2 E cable of the Potentiostat is connected to Input 2 Note that galvanostat mode is not available with the Pi
115. tandby O Potentiostat Select Dummy Galvanostat ga lva nostat OReal ORA operation Ohighz pera Mains filter Invert Y High Stability IR Compensation Applied current Range 1 yA Level 0 0000 A a 9 Set applied current as baseline Access Current channel units conversion dialog Figure 5 18 Set applied current Current i channel units conversion Set units conversion on the Current i channel to Use these va lues to set Units Conversion for the Current channel 0Y 0n4 1 100n4 78 eDAQ Potentiostats Figure 5 19 The Chart Stimulator dialog box when the Potentiostat is in Galvanostat mode Chart software on Windows computers To switch to the Galvanostat mode of operation choose the Potentiostat command in the Channel Function pop up menu to open the control window and turn on the Galvanostat and Dummy radio buttons Figure 5 17 When in Galvanostat mode the current and potential signals will be reversed from normal potentiostatic operation That is the I Out cable will be carrying the potential signal which will now appear on Channel 1 and the E Out cable the current signal which will now appear on Channel 2 You will need to configure the Units Conversion of Channel 2 so as to ensure that the current signal is recorded in the correct current units Figure 5 18 When the Chart Stimulator command Setup menu is selected it
116. the I2C cable to the 12C connector on the back panel of the e corder and the other the other end to the 12C Input connector on the back panel of the Picostat Use the three BNC cables to connect the back panel of the Picostat to the front panel of the e corder as in Table 3 2 Picostat rear panel e corder front panel Out Input 1 E Out Input 2 E In Output Picostat rear panel e corder front panel Out Input 1 E Out Input 2 E In Output Chapter 3 The Picostat 31 Figure 3 5 The Picostat shown connected to an e corder front view Figure 3 6 The Picostat shown connected to an e corder back view Overload Picostat e corder 401 en Power Status river AS AAA With these connections when you use the software to set a more positive voltage a more oxidising potential will be applied at the working electrode Such an arrangement is shown in Figure 3 5 and Figure 3 6 To operate the Picostat with the reverse polarity make the connections shown in Table 3 3 With these connections when you use the software to set a more positive voltage a more reducing potential will be applied at the working electrode Check that all connectors are firmly attached Loose connectors can cause erratic behaviour or may cause the P
117. the software such as EChem Chart or Scope has located and initialised the Potentiostat If the light does not go on when the software is run check that the Potentiostat is properly connected If there is still a problem please refer to Appendix B page 95 The Overload Indicator Located on the left hand side of the front panel is the Overload indicator Figure 2 1 When lit this indicates that the Potentiostat is or has gone out of compliance which usually occurs because of an open circuit or excessive resistance in the electrochemical cell Higher resistances can be often be encountered when electrodes are fouled by the products of electrolysis reactions The Potentiostat tries to compensate by increasing the compliance potential that is the potential between the auxiliary and working electrodes If the compliance voltage exceeds specification about 11 V potential control of the cell is lost and drifting or oscillation of the signal can be seen Any data collected during this period is unreliable and should be discarded The Overload indicator will light as soon as there is an overload and will stay on until the recording has stopped If the indicator light comes on repeatedly and your connections are good then try bringing your electrodes closer together and or increasing electrolyte concentration and or modifying your experimental conditions to avoid fouling of the electrodes Redesigning your electrochemical cell may be
118. ther QuadStat or other eDAQ Amp More information about the 12C connector can be found in your e corder Manual Grounding Connector The QuadStat back panel Figure 4 2 has a 4 mm grounding socket This enables connection of a Faraday cage with the green grounding cable included with the QuadStat the use of which can greatly diminish electrical noise The construction of the Faraday cage can range from a simple cardboard box covered with aluminium foil in which the electrochemical cell is located to a more sophisticated copper mesh enclosure or sheet metal box In all cases it is essential that the Faraday cage be electrically grounded to act as an effective shield against electrical interference The QuadStat itself is grounded via its connection to the e corder unit which is in turn earthed via the three pin mains power connector It is also important that the power socket that you are using is well earthed You can try grounding the Faraday cage via its own connection to earth or via the QuadStat ground cable but not by both methods simultaneously The purpose of this ground cable to the Faraday cage is to provide an easy means of grounding the cage please note that it is not for grounding the QuadStat itself If your Faraday cage is already earthed by its own ground connection then you should not use the QuadStat ground cable Use of the QuadStat cable in this instance will 46 eDAQ Potentiostats Figure 4 5 S
119. tion Dimensions h xw x d 50 x 76 x 260 mm 1 96 x 3 0 x 10 2 inches Weight 0 8 kg 1 8 Ib Operating conditions 0 35 C O 90 humidity non condensing eDAQ reserves the right to alter these specifications at any time Appendix C Specifications 105 QuadStat Electrometer amp Power Amp Compliance voltage Maximum control voltage Output current Input impedance Input bias current gt 11V 2 5 V using internal control 10 V using external input mA maximum 10130 1 pF lt pA 25 C Current Measurement and Control Current ranges I V Gain I V Multiplier DC current error Current signal offset Bandwidth unfiltered Low pass filter e corder filter settings Drift with temperature Control Port 12C input and output Power requirements mA 500 200 100 50 20 10 5 2 1 pA 500 200 200 50 20 10 5 2 nA 100 10 1 nA V xl x1000 lt 1 FS on ranges of 2 pA 1 mA lt 0 5 FS on ranges of 2 nA 1 pA 400 pA on ranges 2 pA 1 mA 400 nA on ranges 2 nA 1 pA gt 10 kHz on ranges of 2 pA 1 mA 1 kHz on ranges of 2 nA 1 pA 10 Hz 3rd order Bessel 10 kHz to 1 Hz in 10 5 2 steps lt 10 pV C Male and female DB 9 pin connectors Provides control and power 17 VDC 20 mA 8 V DC 20 mA 0 6 W quiescent 106 eDAQ Potentiostats Physical Configuration Dimensions h xw xd 60 x 150 x 200 mm 2
120. tors can cause erratic behaviour or may cause the QuadStat to fail to work Each QuadStat channel uses two e corder input channels during normal operation for recording of the current and potential signals The remainder of this chapter assumes that you have connected the current signal of QuadStat channel 1 to e corder Input 1 and the potential signal to e corder Input 2 and other channels as shown in Table 4 2 and Figure 4 5 It is also possible when using Chart or Scope software to connect the QuadStat to other e corder input channels in which case the description that follows would change accordingly Chapter 4 The QuadStat 49 Figure 4 8 Correct use of two channels with a common auxiliary and reference electrode The auxiliary and reference leads of channel 2 are joined together When using EChem software e corder Input 1 is always set to be the current signal the channel and e corder Input 2 is automatically set to be the potential signal the E channel Thus when using EChem software connect the QuadStat Channel 1 current signal I Out to e corder Input and the QuadStat Channel 1 potential signal E Out to e corder Input 2 Other QuadStat channels remain unconnected To record the applied potential signals E Out of a QuadStat with Chart and Scope software first configure the settings of the standard Input Amplifier dialog box described in the Chart and Scope Software Manuals Using a Common Re
121. turn earthed via the three pin mains power connector It is of course important that the power socket that you are using is well earthed Connecting the Potentiostat Your Potentiostat will have been supplied with an 12C cable DB 9 pin connectors at either end and three cables with BNC connectors at either end First make sure that the e corder is turned off Then connect the 12C cable to the 12C connector on the back panel of the e corder and the other the other end to the 12C Input connector on the back panel of the Potentiostat Use the three BNC cables to connect the back panel of the Potentiostat to the front panel of the e corder as shown in Table 2 2 With these connections when you use the software to set a more positive voltage a more oxidising potential will be applied at the working electrode Potentiostat rear panel e corder front panel Out Input 1 E Out Input 2 E In Output Potentiostat rear panel e corder front panel Out Input 1 E Out Input 2 E In Output Chapter 2 The Potentiostat 11 Figure 2 5 The Potentiostat shown connected to an e corder front view as described in Table 2 2 Figure 2 6 The Potentiostat shown connected to an e corder back view Power Status s0 Such an arrangement is shown in
122. ually has a value of between 10 and 107 cm2 s Appendix D Electrochemical Equations 111 Chronocoulometry The Integrated Cottrell Equation The current response equation at a planar electrode for a chronocoulometric experiment is the time integrated form of the Cottrell equation t 1 2 7 12 2nFAD Ct 0 1000x where Q the number coulombs transferred n the number of electrons transferred to or from the substrate molecule A area of the exposed surface of the electrode cm D diffusion coefficient of the substrate molecule cm2 s C concentration of the substrate molecule mol L f time s k a constant Thus a plot of Q versus 1 2 should produce a straight line with an intercept of k which in turn can be defined as k nFAI Qu where T surface concentration of adsorbed substrate mol cm Quy double layer charging 112 eDAQ Potentiostats Lenao O Overload Index Picostat A amperometric sensors 84 amperometry 61 82 Applied Current Potentiostat Galvanostat 21 Applied Potential Potentiostat 21 autozero QuadStat 57 B back panel Picostat 29 Potentiostat 9 QuadStat 45 baseline zero QuadStat 57 biosensors 85 Bridge Amp 2 C calibration multiple point 85 non linear 85 potentiostat current signal 19 two point linear 85 ZRA current signal 19 checking procedure 3 chronoamperometry 65 111
123. uld be employed whenever possible However it should not be used for either pulse amperometric or voltammetric experiments where the pulses are shorter than 100 ms or for voltammetric experiments where fast scan rates greater than 100 mV s are used or for other signals which are likely to exhibit fast rise or fall times otherwise excessive smoothing of the signal may occur In addition with Chart and Scope software there is a Mains Filter checkbox If this is ticked then the e corder will apply a mains filtering algorithm to the incoming signal which removes repetitive signals occurring at 50 or 60 Hz which are typical of mains interference Note that the mains filter is not a notch filter and can remove 50 or 60 Hz interference even if it is not a pure sinusoidal function However the mains filter does take a few seconds to learn the pattern of the interference so that you will need to record for longer than this for it to take full effect The mains filter can be employed even for experiments in which there are sudden potential jumps Inverting the Signal m The Invert checkbox allows you to invert the incoming current signal It provides a simple way to redefine the directions up or down of an anodic or cathodic current signal This control does not affect the direction of current flow at the electrodes Cell Control 2 Real The Picostat can be in one of two operating modes controlled by the Cell radio b
124. us a truly reversible reaction can be identified by examining the adherence of the system to the following functions lo Y Ep independence of the scan rate v In addition cyclic voltammograms will exhibit IE Eo z mV at 298 K ba le When working in highly resistive solutions which is often the case when using organic solvents for cyclic voltammetry the reference electrode should be kept as close as possible to the working electrode to minimise iR drop Nonetheless there may still be an appreciable uncompensated resistance which will cause E Ep to become larger than predicted the peaks to be broader and the peak currents to be smaller 110 eDAQ Potentiostats Chronoamperometry The Cottrell Equation When chronoamperometry is performed on an unstirred solution at a planar electrode the faradaic current response is described by the Cottrell equation _nFAD 2C 10001 242 where n the number of electrons transferred to or from the substrate molecule F Faraday s constant 96485 C mol A area of the exposed surface of the electrode cm D diffusion coefficient of the substrate molecule cm2 s C concentration of the substrate molecule mol L f time s The factor of 1000 is to bring both cm and dm 1 dm 1000 cm 1 L in the equation to common units Thus a plot of i versus 1 y t should produce a straight line In aqueous solution the coefficient of diffusion us
125. uttons e Standby If Standby mode is selected the auxiliary and reference electrodes are isolated by an internal relay which effectively means that all the electrodes are at a floating potential and that no current Chapter 3 The Picostat 37 will be passed through your experimental solution The electrodes will not be connected until the Picostat control dialog is closed and the Chart Scope or EChem Start button is clicked to begin a scan The Applied Potential control is disabled in this mode e Real In Real mode the electrodes will be active and the Applied Potential slider control can be used to adjust the potential When you close the control dialog using EChem or Scope software the Picostat will revert to Standby mode until the Start button is clicked to begin a scan If you are using Chart or Scope software the Picostat will remain in Real mode when the dialog is closed this allows you to start and stop recording data while the electrodes remain active which allows periodic recording of the signal from amperometric biosensors or in vivo electrodes without disturbing the environment around the electrodes Applied Potential 0 0000 Y Applied Potential SUY The applied potential slider control is only enabled in Real mode lt allows you to adjust the voltage applied to the electrodes To change the value simply drag the control left or right to set an appropriate potential or use the text entry contro
126. verted to AgCl although you may wish to remove the old coating completely and re chloridize the silver wire to ensure a good coating of fresh AgCl In either case replace the newly coated wire back into the electrode casing with freshly prepared KCI solution Aged calomel Hg Hg Cl electrodes should usually be replaced Reference electrodes using a gelled electrolyte will deteriorate if the gel dries out The results show peaks in the negative current direction when you want them in positive direction e Check that the Invert box is checked or not as appropriate for the current recording channel See Inverting the Signal on page 18 page 37 or page 56 Appendix B Troubleshooting 97 The results show peaks or steps at different potentials than you expect e See previous section e Make sure the reference electrode is connected to the correct yellow lead wire e Check the condition of the reference electrode All reference electrodes age For example and Ag AgCl electrode will age with exposure to light Eventually the white light grey coating of AgCl on the central silver wire will be replaced by a brown black coating of silver oxide As this process takes place the apparent positions of your voltammetric peaks will appear to shift to different potentials Most Ag AgCl electrodes can be quickly regenerated by placing the silver wire in 1 M hydrochloric acid solution for a minute or two any silver oxide is quickl
127. y reconverted to AgCl although you may wish to remove the old coating completely and re chloridize the silver wire to ensure a good coating of fresh AgCl Replace the newly coated wire back into the electrode housing and refill with freshly prepared KCI solution Aged calomel Hg Hg2Cl electrodes should usually be replaced Reference electrodes using a gelled electrolyte will deteriorate if the gel dries out The results are contaminated by noise e Most often the noise encountered in electrochemical experiments is a manifestation of mains hum 50 or 60 Hz interference from power lines and mains powered equipment Note that depending on the sampling rate aliasing can make such interference appear as a low frequency oscillation superimposed on your data Ensure common grounding by attaching the e corder and computer to the same power board which is then attached to a three pin grounded power socket If consistent with the bandwidth required by your experiment use the 10 Hz or lower filter of to record your results see page 17 page 37 and page 55 Get an electrical technician to check that the grounding of the power socket itself is in good condition Try the Mains Filter setting Chart and Scope software which is very effective at removing main induced artifacts e Check electrode connections Poor electrical contact to the electrodes will act as a source of noise Particularly check the electrode cables cables age espe

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