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Appendix A — Technical Aspects

81

QuadStat

The QuadStat comprises 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

Within the QuadStat an ‘error voltage’ is generated from the difference
between the voltage on the Reference electrode and ground (0 V). This
error voltage drives a high gain amplifier (VCVS – voltage controlled
voltage source) the output of 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, equal to
the desired Command voltage. The current flow (I) in the Working
Electrode (WE) is the quantity being measured. A DAC provides a
means to offset (zero) this current signal so that small current signal
variations can be more accurately determined.

Overload

Auxiliary

Reference

Working

Online

Dummy

Cell

Hi Z

Ref Amp

Gain

Power Amp

Error Voltage

Subtractor

Overload Detector

Front Panel

Back Panel

E In
(Command
voltage)

E Out
(Working
voltage)

I Out

I

2

C Input

I

2

C Control

Interface

Low–pass
Filter

I to V

+
–

I

2

C Output

Shield

Shield

I Offset

E Offset

+

–

+
+

To QuadStat channels 2, 3, and 4

Σ

+

–

DAC

DAC

PGA

+
–

Σ

Σ

Figure A–3

Block diagram of the
QuadStat, Channel 1.

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87
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Summary of Contents for e-corder

Page 1: ...Potentiostats Potentiostat Dual Picostat QuadStat WE WE WE WE QuadStat RE RE RE RE AE AE AE AE Channel 1 Channel 2 Channel 3 Channel 4 164 Potentiostat Overload Dual PicoStat 362 Status Power Trigger Overload Overload Channel 1 Channel 2 ...

Page 2: ...od 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 Windows XP Vista and Windows 7 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 Prod...

Page 3: ...rode Connectors 22 Electrode Cable 23 The Power Indicator 23 The Status Indicator 24 The Overload Indicator 24 The Back Panel 25 Power Connector On Off 25 E Out I Out and E In Connectors 25 USB socket 26 I2 C Connectors 26 Grounding Connector 26 Connecting the Dual Picostat 27 First Use 30 Dual Picostat Control Window 30 Maintenance 37 4 The QuadStat 39 The Front Panel 40 Electrode Connectors 40 E...

Page 4: ...metry 67 Chart software 69 Controlled Potential Electrolysis 70 Controlled Current Electrolysis 71 Amperometric Sensors 72 Biosensors 73 Microdialysis Sensor 73 Dissolved Oxygen dO2 Sensors 74 Nitric Oxide NO Sensors 75 A Technical Aspects 77 Potentiostat 77 Dual Picostat 79 QuadStat 81 B Troubleshooting 85 C Specifications 91 Potentiostat 91 Dual Picostat 94 QuadStat 96 D Electrochemical Equation...

Page 5: ...QuadStat EA164 Chapter 4 Four channel three electrode potentiostat with gain ranges of 200 pA to 10 mA They are designed for use with an 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 NOTE This manual is for the EA163 Potentiostat EA362 Dual Picostat a...

Page 6: ...ng various voltammetric and amperometric experiments under full software control and are automatically recognised by the Chart Scope or EChem software which control their gain range signal filtering and other settings See our web site at www eDAQ com for more information Checking the unit Before you begin working with your Potentiostat Dual Picostat or QuadStat please check that all items describe...

Page 7: ...support edaq com to obtain the correct document IMPORTANT Always make sure that the e corder is turned off before you connect or disconnect 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 EA161 Potentiostat then you will notice it is very similar to the new EA163 Potentiostat which has higher bandwidth 100 kHz...

Page 8: ... 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 Potentiostat Overload Overload indicator light Electrode connector Lemo socket to electrodes Online indicator light Working Electrode Auxiliary Electrode Reference Electrode Shield Reference Electrode Working Electrode Shiel...

Page 9: ...orking green and auxiliary red leads to the two electrodes or circuit test points across which to measure the current page 14 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 yell...

Page 10: ...istance 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 drif...

Page 11: ...Panel The back panel of the Potentiostat is shown in Figure 2 3 BNC output connectors DB 9 pin I2 C connectors 4 mm socket ground connector BNC input connector Digital Ground Regulated 17 V DC Regulated 8 V DC Regulated 17 V DC Power lines SCL DSC SDA DSD INT I2 C control signals Digital Ground Regulated 17 V DC Regulated 8 V DC Regulated 17 V DC SCL DSC SDA DSD INT I2 C control signals Input Outp...

Page 12: ...nt to connect the Potentiostat to other e corder input channels I2 C Connectors The Potentiostat back panel Figure 2 3 has two DB 9 pin I2 C 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...

Page 13: ...ated copper mesh enclosure or sheet metal 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 turn earthed via the three pin mains power connector It is of course important that the power socket that you are using is w...

Page 14: ... 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 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 Trigger Power Status Output Input 1 Input 3 Input 2 Input 4 401 Overl...

Page 15: ...tware you must always connect the current signal I 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 o...

Page 16: ... Standby mode until recording is started Now select Dummy mode operation You will need to adjust the gain range to 20 μA to accommodate your signal amplitude You can now adjust the applied potential with the slider bar or by entering the exact potential with the A button The resulting current signal should obey Ohm s law I E R so that an applied potential of 1 V should produce a current of 10 μA w...

Page 17: ...cting the appropriate radio button 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 I Out Figure 2 3 The potential signal is provided at E Out When two electrode potentiostat operation is required the auxiliary and reference l...

Page 18: ...vered at I 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 sign...

Page 19: ...le 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 If this is ticked then the e corder will apply a mains filtering algorithm to the incoming signal which removes repetiti...

Page 20: ...trol 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 potential applied to the electrodes while the Potentiostat control window is open When you close the control dialog using EChem or Scope software t...

Page 21: ...quired 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 13 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 ...

Page 22: ...edback 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 u...

Page 23: ... 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 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 Applied Current The...

Page 24: ...gnal of 10 μA EA163 or 1 μA EA161 should be obtained when a potential of 1 V is applied 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 ...

Page 25: ... Chart or Scope software or high impedance voltmeter Chart or Scope software The mode of operation is under software control IMPORTANT Always make sure that the e corder is turned off before you connect or disconnect the Dual Picostat Failure to do this may result in damage to the e corder and or the Dual Picostat IMPORTANT The EA362 Dual Picostat supersedes the EA162 Picostat and it has many new ...

Page 26: ...Dual Picostat electrode connectors 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 Dual PicoStat 362 Status Power Trigger Overload Overload Channel 1 Channel 2 Overload indicators Electrode connectors 6 pin Lemo socket to electrodes Working Electrode Auxiliary Electrode R...

Page 27: ...e 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 Dual Picostat make sure that the red dot on the cable connector is aligned with the top of the Dual Picostat electrode connector Figure 3 2 Insert the cable connector and push gently until it locks int...

Page 28: ...ontrol of the sample 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 remain lit and an alarm beep will sound once an overload has occurred even if the overload condition subsequently goes away it will be reset once the scan has finished If the indicator comes on repeatedly and your...

Page 29: ...ide Faraday cages if required E Out I Out and E In Connectors The Dual Picostat back panel has six BNC connectors labelled E out 1 and 2 I out 1 and 2 and E in and Ext Trigger The E in is connected to the Output of the e corder usually Output is used The Dual Picostat provides up to four analog signals the potential signals E out 1 and 2 and the current signals I out 1 and 2 See the section Connec...

Page 30: ...onnector The Dual 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 Dual 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 sophi...

Page 31: ...arth or via the Dual Picostat ground cable but not by both methods simultaneously Connecting the Dual Picostat The Dual Picostat will have been supplied with an I2C cable DB 9 pin connectors at either end and two cables each with three BNC connectors at either end First make sure that the e corder is turned off Then connect the I2 C cable to the I2 C connector on the back panel of the e corder and...

Page 32: ... and Iout 2 and two potential signals Eout 1 and Eout 2 Connect the Picostat as shown in Table 3 3 when used as a bipotentiostat there are two current signals Iout 1 and Iout 2 and one potential signal Eout 1 Connect the Picostat as shown in Table 3 3 Note that it is also possible when using Chart software to connect the Dual Picostat to other e corder input channels but in these cases the discuss...

Page 33: ... operation Single channel or 4 electrode operation I2 C cable Omit this cable for single channel or 4 electrode operation Figure 3 6 The Dual Picostat shown connected to an e corder back view Figure 3 5 The Dual Picostat shown connected to an e corder front view ...

Page 34: ... light Then attach the 10 Mohm test resistor supplied with the Dual 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 and perform the test described in Maintenance page 37 Dual Picostat Control Window With Chart software the Dual Picostat Control window is accessed from the Dual Picost...

Page 35: ...pop up menu Use the Change button to return to Dual Picostat CH1 controls Select the operating mode This number refers to the Chart software channel to which the Iout signal is connected Use the Change button to go to the Dual Picostat CH2 controls to select the operating mode Figure 3 7 Accessing the Dual Picostat controls with Chart software ...

Page 36: ...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 I E R so that with a 10 Mohm test resistor R in place an applied potential E of 1 V should produce a current I of 100 nA while other potential settin...

Page 37: ... to Standby mode until the Start button is clicked to begin a scan If you are using Chart 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...

Page 38: ... and Iout 2 and two potential signals at Eout 1 and Eout 2 If using just one reference electrode in the sample then connect the CH2 reference lead wire to the CH 2 auxiliary lead wire otherwise the CH2 auxiliary red lead wire is left unconnected Four electrode Typically the working electrode from CH1 is positioned on one side of a membrane or interface while the auxiliary and reference electrodes ...

Page 39: ... that you expect to encounter during your experiment If during the experiment the current signal exceeds the range then the data will be truncated Filtering The Off setting gives the full bandwidth of the Dual Picostat which can be up to 16 kHz but which may also be limited by the characteristics of your electrodes and sample solution The Dual Picostat has an internal 10 Hz low pass filter that ca...

Page 40: ...This control does not affect the actual direction of electron flow at the electrodes Applied Potential The applied potential slider control is only enabled in Real mode It allows you to adjust a constant voltage up to 2 5 V applied to the electrodes To change the value drag the slider bar to an appropriate potential or use the text entry controls to enter an exact value A more positive value will ...

Page 41: ...t signals after recording has started then you can use the Zero All Inputs command in the Chart software Setup menu Figure 3 9 Maintenance The Dual Picostat will not require maintenance during daily operation However you should periodically check it for optimum results First set up the Dual Picostat and e corder as outlined earlier in this Chapter Connect the electrode cables connected and attache...

Page 42: ...ur connections of the Dual Picostat to the e corder page 27 Then check with the second electrode cable If the problem persists then it is possible that the Dual Picostat itself needs repair If one electrode cable works well but the second does not then it is likely you have a faulty cable replacements can be obtained from your eDAQ supplier If these tests indicate that the Dual Picostat is working...

Page 43: ...rometric sensors such as those used for dissolved oxygen electrodes nitric oxide electrodes or enzymatic biosensors It can also be used for experimentation with multiple small scale fuel cells e g microbial fuel cells small solar panels and mini batteries or other small power sources Note that when used with EChem software only a single QuadStat channel can be used With Scope software one or two c...

Page 44: ... The QuadStat is supplied with appropriate electrode cables with each lead terminated by an alligator clip 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...

Page 45: ...t the QuadStat has overloaded which usually occurs because it has gone out of compliance because of an open circuit such as an unconnected AE or faulty electrode or the resistance is too high in the electrochemical cell 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 pote...

Page 46: ... 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 4 mm socket ground connection DB 9 pin I2C connectors 20 pin socket for screw terminal adaptor Figure 4 3 Input and output signals 20 pin terminal adaptor Push firmly into socket Figure...

Page 47: ... QuadStat overload indicators to light The Back Panel The back panel of the QuadStat is shown in Figure 4 2 E Out I 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 I Out E Out E In and COM for each QuadStat channel Channels 1 4 The COM common pins are provided for co...

Page 48: ...inst 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 o...

Page 49: ... 5 4 3 2 1 To e corder 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 To e corder Output or waveform generator Single channel operation Multiple channel operation with the same applied waveform on each channel To e corder Output or waveform generator Figure 4 6 Using the external inputs of the QuadStat Note connec...

Page 50: ... 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...

Page 51: ...mal 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 Trigger Power Status Output Input 1 Input 3 Input 2 Input 8 821 I...

Page 52: ...ied potential signals E Out of a QuadStat with Chart and Scope software first configure the settings of the standard Channel 2 Channel 4 Channel 3 Channel 1 164 QuadStat RE RE RE AE AE AE AE Channel 2 Channel 4 Channel 3 Channel 1 164 QuadStat RE RE RE AE AE AE AE Channel 1 auxiliary reference and working leads to be connected to AE1 RE1 and WE1 Channel 2 auxiliary and reference leads connected to...

Page 53: ...overload lights on these channels will come on but this does NOT indicate a fault condition Only the overload light of Channel 1 where the reference and auxiliary electrodes are connected is now 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 this waveform can be effect...

Page 54: ...ow an overload light but in this case there is no fault condition 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 Qua...

Page 55: ...el or OK the QuadStat will revert to Standby mode until recording is started For now select the Dummy cell mode which connects an internal 100 kohm resistor between the electrodes You will need to adjust the gain range to 50 μA 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 ba...

Page 56: ... labels to adjust axis scaling Select QuadStat from the Channel Function pop up menu Click the QuadStat button Current signal display area Figure 4 9 Accessing the QuadStat controls with Chart software Figure 4 10 Accessing the QuadStat controls with Scope software ...

Page 57: ...t 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 Filtering 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 charact...

Page 58: ...thodic current signal This control does not affect the direction of current flow at the electrodes Cell Control The QuadStat can be in one of three operating modes controlled by the Cell radio buttons 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 cu...

Page 59: ...lied Potential The Applied Potential control offsets the voltage up to 2 5 V applied to either the dummy cell or external working electrodes This potential Eoff is remembered by the QuadStat and will be applied when you start a scan if the checkbox is ticked Note that each QuadStat channel may have a different value for Eoff This potential value will be summed with any external input waveform Ein ...

Page 60: ...d Control page 96 The amount of current offset is reported in the text box 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 Figure 4 11 QuadStat Potential Window When using the QuadStat with Chart software it is possible to alter the applied potentials during recording Access the QuadStat Applied Poten...

Page 61: ...he dummy cell and E is the applied potential Thus a signal of 10 μA 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 pr...

Page 62: ...58 eDAQ Potentiostats ...

Page 63: ... 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...

Page 64: ... experiments Linear Scan techniques page 61 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 Chronoamperometry page 62 page 64 Amperometry Constant Potential Electrolysis page 70 monitor the current signal at fixed potentials C...

Page 65: ...er time response characteristics 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 el...

Page 66: ...rnal QuadStat Applied Potential page 55 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 cable which the...

Page 67: ...or mode Potential waveform generated by the Stimulator settings above Settings to produce a 500 mV amplitude 1 Hz square wave on a base potential of 200 mV Use the Stimulator command to access the Stimulator applied potential waveform controls Figure 5 2 Figure 5 3 Figure 5 2 Chart Stimulator waveform output controls Figure 5 3 Stimulator controls for multiple step chronoamperometry Figure 5 1 Cha...

Page 68: ...wards 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 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 cho...

Page 69: ...try 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 the total charge transferred the total number of coulombs or electrons transferred is equal to the integrated current the settings used for chronoamperometry page 62 can also be used for chronocoulometry...

Page 70: ...gral 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 5 For more information refer to the Computed Input section in the Chart Software Manual Select Integrate in the Function menu Figure 5 6 Integration of the current signal using Scope Computed Functions Figure 5 5 Online integration of th...

Page 71: ... 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 whic...

Page 72: ...ero 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 14 Select the expected range for the potential signal Potential signal is displayed when in Galvanostat mode Select galvanostat operation Select Potentiostat in the Channel menu Set applied current Use these values to set Uni...

Page 73: ...re 5 8 When the Chart Stimulator command Setup menu is selected it accesses the Stimulator dialog box which when using galvanostat mode allows a baseline and various current waveforms to be configured Figure 5 9 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 greate...

Page 74: ... Chronocoulometry page 65 and this can be used to determine the extent of reaction 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 If the reaction causes the formation of a polymer film on the electrode for example pyrrole to po...

Page 75: ...hniques are essentially the same as Chronopotentiometry page 67 and require the use of a galvanostat The Potentiostat when 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 ...

Page 76: ... 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 The polarising 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 potent...

Page 77: ...eferred to as biosensor meters The first step is to establish the polarising voltage and current measurement requirements of your sensor 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 55 Many biosensors provide a linear signal response over a range of concentrat...

Page 78: ...vity 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...

Page 79: ... counter electrode to which the reference and auxiliary electrode leads are attached Usually an oxidising polarising voltage applied potential of up to 1 0 V is required at the working electrode to effect the reaction 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 po...

Page 80: ...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 and isoPod have 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 55 ...

Page 81: ...signed 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 I2 C bus which also supplies DC power Potentiostat The Potentiostat is designed to function as a potentiostat Chart Scope or EChem sof...

Page 82: ...trode 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 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 ...

Page 83: ...nd 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 Dual Picostat and the electrochemical cell to which it is connected forms a composite feedback control system in which the va...

Page 84: ...dance 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 Dual Picostat has three gain ranges of 100 pA V 1 nA V and 10 nA V The maximum current output signal I Out is 10 V at any gain setting Se...

Page 85: ...rm 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 equal to the desired Command voltage The current flow I in the Working Electrode WE is the quantity being measured A DAC provides a means to offset zero this current signal so that small current signal varia...

Page 86: ...internal E Offset DAC In particular note that this E Offset adjustment is added to any signal applied at E In so that the final potential at the WE is the sum of these two values 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 pres...

Page 87: ... 44 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 ...

Page 88: ...84 eDAQ Potentiostats ...

Page 89: ...our eDAQ representative The On line indicator fails to light when the software is opened Check that the e corder is connected to the mains power and that it is turned on Check that Potentiostat Dual Picostat or QuadStat is properly connected to the e corder and that the cables are not loose Especially check that the E in I Out and E Out cables are correctly connected see page 9 page 28 and page 46...

Page 90: ...erload indicator is on a potential overload has occurred Check that the electrode cables are firmly attached to the electrodes Check that the surfaces of the electrodes have not become fouled The Dual 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 Dual Picostat or QuadStat controls or sta...

Page 91: ...e 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 hyd...

Page 92: ...Hg2Cl2 electrodes should usually be replaced Reference electrodes using a gelled electrolyte will deteriorate if the gel dries out The results are contaminated by noise 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 i...

Page 93: ...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 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 ref...

Page 94: ...90 eDAQ Potentiostats ...

Page 95: ...ce voltage 10 V Output current 100 mA maximum Current limit 200 mA Slew rate 3 V μs Electrometer Input resistance 1013 ohm Input bias current 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 μV C Gain accuracy 0 1 ...

Page 96: ...t ranges 10 mA or larger Drift with temperature 0 3 mV C Control Loop Voltage offset error 1 mV Voltage gain error 0 1 Bandwidth unity loop gain 100 kHz EA163 16 kHz EA161 90 lag 160 Hz high stability mode 90 lag Ramp follower error 1 mV 100 V s 1 mV 1 V s high stability mode Current Range Setting Potentiostat gain μA V 100 50 20 mA 10 000 10 5 2 mA 1 000 1 mA 500 200 μA 100 100 50 20 μA 10 10 5 2...

Page 97: ...hysical Configuration Dimensions h w d 50 76 260 mm 1 96 3 0 10 2 inches Weight 0 8 kg 1 8 lb Operating conditions 0 35 C 0 90 humidity non condensing eDAQ reserves the right to alter these specifications at any time Current Range Setting Compensation Range 100 50 20 mA 0 10 ohm 10 5 2 mA 0 100 ohm 1 mA 500 200 μA 0 1 kohm 100 50 20 μA 0 10 kohm 10 5 2 μA 0 100 kohm 1 μA 500 200 nA 0 1 Mohm 100 50...

Page 98: ... nA 0 5 FS on ranges of 2 nA 10 μA Filter setting 10 Hz low pass 3rd order Bessel e corder filter settings 2 kHz to 1 Hz in 10 5 2 steps Drift with temperature 20 μV C Control Port I2 C input and output Male and female DB 9 pin connectors Control of the Dual Picostat Current Range Setting Gain nA V Current Offset Bandwidth Hz 10 5 2 μA 10 000 100 μA 5000 1 μA 500 200 nA 1 000 10 μA 5000 100 50 20 ...

Page 99: ...nts 12 V DC 2 A 8 V DC 20 mA Physical Configuration Dimensions h w d 50 76 260 mm 1 96 3 0 10 2 inches Weight 0 8 kg 1 8 lb Operating conditions 0 35 C 0 90 humidity non condensing eDAQ reserves the right to alter these specifications at any time ...

Page 100: ...V on 10 mA range 7 5 V on 5 mA range 10 V on other ranges Maximum control voltage 2 5 V using internal control 10 V using external input Output current 1 mA maximum Input impedance 1013 ohm 1 pF Input bias current 1 pA 25 C Current Range Setting Gain nA V Current Offset Bandwidth kHz 10 5 2 1 mA 500 200 μA 1 000 000 10 mA 10 100 50 20 μA 100 000 1 mA 10 10 5 2 μA 10 000 100 μA 10 1 μA 500 200 nA 1...

Page 101: ...ovides control and power Power requirements 17 V DC 20 mA 8 V DC 20 mA 0 6 W quiescent Physical Configuration Dimensions h w d 60 150 200 mm 2 4 5 9 7 9 inches Weight 1 5 kg 3 3 lb Operating conditions 0 35 C 0 90 humidity non condensing eDAQ reserves the right to alter these specifications at any time ...

Page 102: ...98 eDAQ Potentiostats ...

Page 103: ...al where this occurs is given by where current peak during anodic scan A current peak during cathodic scan A potential at current peak for anodic scan V potential at current peak for cathodic scan V 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 cm2 for an oxidation anodic s...

Page 104: ...ollowing functions Ep independence of the scan rate υ In addition cyclic voltammograms will exhibit mV at 298 K 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 resis...

Page 105: ...trate molecule F Faraday s constant 96485 C mol A area of the exposed surface of the electrode cm2 D diffusion coefficient of the substrate molecule cm2 s C concentration of the substrate molecule mol L t time s The factor of 1000 is to bring both cm and dm 1 dm3 1000 cm3 1 L in the equation to common units Thus a plot of i versus 1 Ðt should produce a straight line In aqueous solution the coeffic...

Page 106: ...ns transferred to or from the substrate molecule A area of the exposed surface of the electrode cm2 D diffusion coefficient of the substrate molecule cm2 s C concentration of the substrate molecule mol L t time s k a constant Thus a plot of Q versus t1 2 should produce a straight line with an intercept of k which in turn can be defined as k nFAΓ Qdl where Γ surface concentration of adsorbed substr...

Page 107: ...tion 65 101 integrated form 102 current signal calibration Potentiostat 17 current signal zero Dual Picostat 36 QuadStat 55 cyclic voltammetry 59 61 99 D differential pulse voltammetry 59 dissolved oxygen sensor 74 Dual Picostat 2 Modes of operation 34 Power Connector 25 Dummy cell Potentiostat 16 QuadStat 54 E E In connector Dual Picostat 25 Potentiostat 8 QuadStat 43 E Out connector Dual Picosta...

Page 108: ...or Dual Picostat 26 Potentiostat 8 QuadStat 44 H high impedance voltmeter Dual Picostat 33 Potentiostat 5 14 High Stability Potentiostat 16 High Z mode Potentiostat 14 Potentiostat electrode connection 5 I I Out connector Dual Picostat 25 Potentiostat 8 QuadStat 43 I2 C connector Dual Picostat 26 Potentiostat 8 QuadStat 43 input amplifier 11 30 49 integrated Cottrell equation 102 iR Compensation 9...

Page 109: ...entials window 56 R Randles Sevcik equation 99 Real cell Picostat 33 Potentiostat 16 QuadStat 54 reference electrode aging and regeneration 88 S sensors amperometric 72 biosensors 73 dissolved oxygen 74 microdialysis 73 nitric oxide 75 signal offset Dual Picostat 36 QuadStat 55 signal zero Dual Picostat 36 QuadStat 55 specifications Potentiostat 91 QuadStat 96 square wave voltammetry 59 Standby ce...

Page 110: ...106 eDAQ Potentiostats Z zero offset 36 55 zero resistance ammeter Dual Picostat 33 Potentiostat 14 ZRA mode Potentiostat 14 Potentiostat electrode connection 5 ...

Page 111: ... notify us before return of the instrument and we 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 been m...

Page 112: ...or Picostat the type of computer and operating system being used for example Windows XP Vista Windows 7 or 8 the software version you are using for example Chart v5 5 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 Wal...

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