eDAQ Potentiostats, User Manual

Potentiostat,Picostat &QuadStat
Overload

Overload

Potentiostat

QuadStat
164

Picostat

Channel 1

AE

RE

Channel 3

WE

WE

AE

e-corder®

Channel 2

Channel 4

AE

AE

RE

WE

WE

RE

RE

www.eDAQ.com

This document was, as far as possible, accurate at
the time of printing. Changes may have been madeto the software and hardware it describes sincethen: eDAQ Pty Ltd reserves the right to alterspecifications as required. Late-breaking information
may be supplied separately. Latest information andinformation and software updates can be obtained
from our web site.

Products: Potentiostat (EA161)
Picostat (EA162)
QuadStat (EA164)

Trademarks of eDAQ

eDAQ Pty Ltd
6 Doig Avenue
Denistone East, NSW 2112
Australia

e-corder and PowerChrom are registered trademarksof eDAQ Pty Ltd. Specific model names, such as
e-corder 201, PowerChrom 280, Picostat and
QuadStat are trademarks of eDAQ Pty Ltd. Chartand Scope are trademarks of ADInstruments Pty Ltd
and are used under license by eDAQ. EChem is atrademark of eDAQ Pty Ltd.
Other Trademarks

Document Number: UM-EA161/2/4-0605
Copyright © June 2005

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.

Mac OS, and Macintosh, are registered trademarksof Apple Computer, Inc. Windows 98, Windows
Me, Windows 2000, and Windows XP aretrademarks of Microsoft Corporation.
PostScript, and Acrobat are registered trademarks ofAdobe Systems, Incorporated.
All other trademarks are the properties of theirrespective owners.

ii

eDAQ PotentiostatsOverloadPotentiostat

Contents

1 Overview 1
How to Use this Manual 2eDAQ Amps 2
Checking the unit 3

2 The Potentiostat 5
The Front Panel 6
The Input Connector 6
Electrode Cable 7
The Online Indicator 8
The Overload Indicator 8
The Back Panel 9
E Out, I 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
Input Connector 26
Electrode Cable 27

Potentiostat & Picostat

The Online Indicator 27
The Overload Indicator 28
The Back Panel 29
E Out, I Out and E In Connectors 29
I2C Connectors 29
Grounding Connector 30
Connecting the Picostat 31
First Use 33
Picostat Control Window 36
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, I Out and E In Connectors 45
I2C Connectors 45
Grounding Connector 46
Connecting the QuadStat 47
First Use 50
QuadStat Control Window 51
Maintenance 56iii

5 Techniques 57

D Electrochemical Equations 105

Introduction 58
Linear Scan Techniques 59
Fast Cyclic Voltammetry 59
Chronoamperometry with Chart 61
On Windows computers 62
On Macintosh 64
Analysis of Chronoamperometry 66
Chronoamperometry with Scope 70
Chronocoulometry 71
Chronopotentiometry 73
Chart software on Windows computers 75
Chart software on Macintosh 76
Scope software 78
Controlled Potential Electrolysis 78
Controlled Current Electrolysis 79
Amperometric Sensors 80
Biosensors 81
Microdialysis Sensor 82
Dissolved Oxygen (dO2) Sensors 82
Nitric Oxide (NO) Sensors 83

Linear Sweep and Cyclic
Voltammetry 105
Chronoamperometry 107
Chronocoulometry 108

Index 109

License & Warranty 113

A Technical Aspects 85
Potentiostat 85
Picostat 86
QuadStat 88

B Troubleshooting 91

C Specifications 97
Potentiostat 97
Picostat 100
QuadStat 102

iv

Potentiostat & Picostat

C H A P T E R

1 Overview

O N E

There are three eDAQ potentiostat models:NOTE
This manual is for the
EA161 Potentiostat. If
you have an older model
EA160 Potentiostat thenplease ask us to send
you the appropriate
manual.

• Potentiostat (EA161), Chapter 2. Single channel, three electrodepotentiostat/galvanostat with gain ranges of 20 nA to 100 mA;• Picostat (EA162), Chapter 3. Single channel, three electrode, highsensitivity potentiostat with gain ranges of 10 pA to 100 nA; and• QuadStat (EA164), Chapter 4. Four channel, three electrodepotentiostat 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 (eDAQ Amps) which are designed for use with thee-corder® system.
Some of the uses of the Potentiostat, Picostat, and QuadStat, arementioned in Chapter 5, and also in the EChem Software Manual
which describes the use of the optional EChem software.

eDAQ Potentiostats1How to Use this ManualThis 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 thesepotentiostats 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 andare automatically recognised by Chart, Scope or EChem software
which control their gain range, signal filtering, and other settings.
The eDAQ Amp family also include the:•pH Amp, suitable for connection of pH, ion selective, andpotentiometric (ORP) electrodes•

Bridge Amp, suitable for sensors requiring a DC Wheatstonebridge connection. Also provides DC excitation•

GP Amp, suitable for high output sensors requiring a highimpedance DC Wheatstone bridge. Also provides DC excitation.

See our web site at www.eDAQ.com for more information.

2eDAQ PotentiostatsChecking the unit
Before you begin working with the Potentiostat, Picostat, or QuadStat
please check that:• all items described in the packing list are included; and that• there are no signs of damage that may have occurred duringtransit.
Contact your eDAQ distributor if you encounter a problem.
You should also become familiar with the basic features of youre-corder system, which are discussed in the e-corder Manual which will
be installed as a pdf file on your computer when you install thesoftware.

Chapter 1 — Overview

34eDAQ PotentiostatsC H A P T E R

T W O

2 The Potentiostat

This chapter describes how to connect and use your model EA161
Potentiostat. If you have an older model EA160 Potentiostat please referto 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 disconnect the Potentiostat. Failure to do this may resultin 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 EA 161 Potentiostat now uses the same
electrode cable as the EA162 Picostat.

eDAQ Potentiostats

5The Front Panel
The front panel of the Potentiostat is shown in Figure 2–1.

The Input Connector
The input connector of the Potentiostat provides connection pins for theWorking, 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 input connector are shown in
Figure 2–2. The Auxiliary and Reference electrode leads have coaxial
shields which are maintained at the respective electrode potential.

Figure 2–1
The Potentiostat front
panel.

Overload
indicator light

Input connector,
Lemo socket,
to electrodes

Overload

Potentiostat

Online indicator light

Alignment dot

Figure 2–2
The Potentiostat input
connector as seen whenlooking at the front
panel.

Working Electrode

Working Electrode Shield

Auxiliary ElectrodeNot connected

Reference Electrode
Reference Electrode Shield

6

eDAQ Potentiostats

Table 2–1
Color–coding on theleads of the electrodecable.

Color

Electrode

Yellow

Reference

Green

Working

Red

Auxiliary

Electrode Cable

To ensure good grip, theelectrode cable alligator
clips use a spring madefrom a good quality steel(stainless steel is
unsuitable for springs).
Avoid wetting of thealligator clips, especiallywith electrolyte solutions
which can hasten
corrosion. If the alligator
clips are wetted then
immediately disconnect
from the Potentiostat,rinse the clips with alittle deionized waterfrom a wash bottle, toremove the electrolyte,
and immediately dry by
patting with paper
tissue. The whole cablemust then be allowed to
dry thoroughly (several
hours at least) before
reuse.
Never immerse any partof the electrode cable inwater, or other liquid!

The Potentiostat is supplied with an electrode cable comprising threeleads, with each lead terminated by an alligator clip. The Reference
and Working electrode leads are shielded to protect the signals fromexternal interference. The alligator clips allow connection to a wide
variety of electrodes, and the leads are color–coded to indicate thetype of electrode to which they should be attached (Table 2–1).
For normal three–electrode potentiostat, or galvanostat, use, thereference 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 attachedto the single ‘counter electrode’. The green lead is attached to theworking electrode.
When using in ZRA (zero resistance ammeter) mode, connect theworking (green) and auxiliary (red) leads to the two electrodes (orcircuit test points) across which to measure the current. 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 areference electrode to measure the potential difference between theleads. The auxiliary lead (red) can be connected to a third electrode (ortest point) to provide a ZRA current signal at E Out, Figure 2–3.

Chapter 2 — The Potentiostat

7

The Online Indicator
Located at the bottom right of the front panel is the Online indicator.,
Figure 2–1. When lit, it indicates that 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 isproperly connected. If there is still a problem, please refer toAppendix B, page 91.

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 (orhas 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 tocompensate by increasing the compliance potential (that is, thepotential between the auxiliary and working electrodes). If thecompliance voltage exceeds specification (about 11 V) potential controlof the cell is lost and drifting, or oscillation, of the signal can be seen.
Any data collected during this period is unreliable and should bediscarded.
The Overload indicator will light as soon as there is an overload andwill 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 yourexperimental conditions to avoid fouling of the electrodes. Redesigning
your electrochemical cell may be necessary. Normally cells aredesigned to keep the reference and working electrodes very close
together, however, when a potential overload occurs, you also need toconsider 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
exceeds the full scale limits of the range setting of the current channel,
and is usually caused by a low resistance between the electrodes.

8eDAQ Potentiostats

BNC output
connectors

Figure 2–3
The Potentiostat backpanel.

E Out

BNC input
connector

I Out

E In

4 mm socket,
ground connection

2

I C
Bus

Input

Output

INT

DSD

SDA

DSC

I2C control signals

SCL

Regulated +17 V DC

Regulated +8 V DC

Regulated –17 V DC

Digital Ground

INT
DSD
SDA
DSC
SCL

Figure 2–4
The pin assignments for
the I2C DB-9 connectors.

Power lines
Regulated –17 V DC
Digital GroundI2C control signals

Regulated +17 V DC
Regulated +8 V DC

DB-9 pin, I2C connectors

1

5

5

1

6

9

9

6

Input

Output

The Back Panel
The back panel of the Potentiostat is shown in Figure 2–3.

E Out, I Out and E In Connectors
The Potentiostat back panel has three BNC connectors labelled E Out,I 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
Potentiostat use e-corder Output +.
Chapter 2 — The Potentiostat

9

The Potentiostat provides two signals: the potential signal (E Out)
indicating the potential difference between the working and referenceelectrodes; and the current signal (I Out) indicating the current flow
between the working and auxiliary electrodes.
For most situations I Out is connected to e-corder input channel 1, andE Out to e-corder input channel 2. However, when you are using Chart
software and recording data from various sources on more that just twochannels you may want to connect the Potentiostat to other e-corder
input channels.

I2C Connectors▲ WARNING!
The I2C connectors arefor the power andcontrol of eDAQ Amps,
page 2, and should not
be used for connection
to any other device.

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 (forgain range and filter selection) to and from the e-corder. A cable isprovided with the Potentiostat for this purpose. The pin assignments areshown in Figure 2–4.
The Output connector can be used for the attachment of other eDAQ
Amps.
More information about the I2C connector can be found in youre-corder 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 toPotentiostat back panel) and an alligator clip (for attachment toFaraday cage). If your Faraday cage is already earthed by its own
ground connection then you should not use this cable (otherwise asecond pathway to earth would exist which could result in a ‘groundloop’ 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.

10

eDAQ Potentiostats

The construction of the Faraday cage can range from a simple
cardboard box covered with aluminium foil, in which theelectrochemical cell is located, to a more sophisticated copper meshenclosure 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 ofcourse important that the power socket that you are using is wellearthed.

Connecting the Potentiostat
Your Potentiostat will have been supplied with an I2C cable (DB–9 pin
connectors at either end), and three cables with BNC connectors ateither end.
First make sure that the e-corder is turned off. Then connect the I2C
cable to the I2C connector on the back panel of the e-corder, and theother the other end to the I2C 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 morepositive voltage, a more oxidising potential will be applied at theworking electrode.

Table 2–2
Potentiostat to e-corderconnections.

Potentiostat rear panel
I Out

Input 1E Out

Input 2

E In

Output –Potentiostat rear panel
Table 2–3
Potentiostat to e-corderconnections, reverse
polarity.

Chapter 2 — The Potentiostat

e-corder front panel

e-corder front panel

I Out

Input 1E Out

Input 2

E In

Output +11

Figure 2–5
The Potentiostat shown
connected to an
e-corder, front view.

Overload

Potentiostat

Input 1401

Input 2

Input 3

Power
Status

OutputInput 4

Trigger

Figure 2–6
The Potentiostat shown
connected to an
e-corder, back view.

Such an arrangement is shown in Figure 2–5 and Figure 2–6.
To operate the Potentiostat with the reverse polarity make theconnections as shown in Table 2–3.
With these connections, when you use the software to set a morepositive voltage, a more reducing potential will be applied at theworking electrode.
Check that all connectors are firmly attached. Loose connectors cancause erratic behaviour, or may cause the Potentiostat to fail to work.

12

eDAQ Potentiostats

The Potentiostat uses two e-corder input channels during normal
operation. The reminder of this chapter assumes that you haveconnected the current signal to e-corder Input Channel 1 and thepotential 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 I channel), and Channel 2 is automatically set to be thepotential signal (the E channel). Thus when using EChem software you
must always connect the current signal (I Out) to Input Channel 1, andthe potential signal (E Out) to Input Channel 2 of the e-corder.
Channel 2 normally displays the applied potential, and its settings arecontrolled using the standard Input Amplifier dialog box, described in
the Chart Software Manual and Scope Software Manual on the eDAQ
Installer CD.

First Use
After you have installed the software, connected the e-corder andcomputer as described with the booklet supplied with the e-cordersystem, and connected the Potentiostat as described above, you areready to begin.
When the e-corder is turned on, and Chart software started, thePotentiostat 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 notrecognised the Potentiostat. Exit the software, check all yourconnections 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 thatno current will flow through your electrodes. To connect to the

Chapter 2 — The Potentiostat

13

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 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/Rso that an applied potential of 1 V should produce a current of 10 µA,
while other potential settings should produce corresponding currents.

Potentiostat Control Window
With Chart software, the Potentiostat Control window is accessed fromthe Potentiostat command in the Channel Function pop-up menu. Figure
2–7 shows the control window on a Windows computer, and Figure

Figure 2–7
Potentiostat controls with
Chart software(Windows).

Select Potentiostat in
Channel pop-up menu
Pause/resume scrolling

Select input range
Select low-passfilter
Selectoperatingmode

Signal display area

Select cell
mode
Stabilization
on/offMains filter
on/offZero pointcalibrations
Signal invert

Applied potential controls

14

iR Compensation controls

eDAQ Potentiostats

Select Potentiostat in the
Channel pop-up menu

Figure 2–8
Potentiostat controls with
Chart software(Macintosh).

Drag ticks andlabels to adjust axis

Select cellmode

Select input
range

Select lowpass filter

Selectoperatingmode

Signal display area

Set applied
potential
Set iR
compensation
Mains filter
on/off

Pause/Resume
scrolling

Axis expansion/
contraction

Invert current
signal

2–8 on a Macintosh computer. These windows control the various
current ranges and filtering options for the Potentiostat.
With Scope software, the corresponding controls are shown in Figure
2–9.

Modes of Operation
The EA161 Potentiostat can be operated in several different modes byselecting the appropriate radio button:• Potentiostat (Chart, Scope or EChem software), described below.
For three–electrode use connect the working (green), reference andauxiliary (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

Chapter 2 — The Potentiostat

15

operation is required the auxiliary and reference leads (red andyellow) should be attached to the single ‘counter electrode’.
• Galvanostat (Chart and Scope software), page 73 – 78. Connect
the electrodes as described for potentiostat operation, above. Noteespecially that the potential signal is provided at I Out, Figure 2–3.
The current signal is provided at E Out.
• ZRA, zero resistance ammeter, (Chart and Scope software).
Connect the working (green) and auxiliary (red) leads to the twoelectrodes (or circuit test points) across which to measure the current,
the current signal is provided at I Out. The reference lead (yellow)
can be connected to a reference electrode (or circuit test point) tomeasure the potential difference to the auxiliary (and working)leads. The high impedance potential signal (if used) is supplied at
E Out, Figure 2–3; or• 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 reference electrode to measure the potential
difference between the leads. The high impedance potential signal
is delivered at I Out. The auxiliary lead (red) can be connected to athird 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 referenceelectrode, if one is being used.

Signal Display
The current signal is previewed in the scrolling display area. Note thatthe signal is not being recorded to hard disk at this stage, and thatwhen 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.

16eDAQ Potentiostats

You can shift or stretch the vertical Amplitude axis to make the best useof the available display area — similar to the amplitude axis in themain Chart, Scope or EChem window.

Setting the Range
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 therange so that it is larger than the biggest current that you expect toencounter during your experiment. If, during the experiment the current
signal exceeds the range, then the signal will go off scale and be lost.

Filtering
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 theremoval of mains hum (50 or 60 Hz interference) and should be
employed whenever possible. However, it should not be used forpulsed 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 amains 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 puresinusoidal 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.

Chapter 2 — The Potentiostat

17

Inverting the Signal
The Invert checkbox, allows you to reassign the direction (up or down)of an anodic (or cathodic) current. Please note that this affects thedisplay of the signal only — it does not reverse the direction of actual
current flow at the electrodes!

Cell Control
The Potentiostat can be in one of three cell modes, controlled by the
Cell radio buttons:• 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 isclicked. This mode is used if you do not wish to alter the state of theexternal cell until the method is actually performed. The Applied
Potential slider bar control is disabled in this mode.
• Dummy: the Potentiostat is connected to the internal 1 MΩ dummycell. You can then use the Applied Potential slider control to vary thevoltage 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 isuseful 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 beused to set the potential applied to the electrodes while thePotentiostat 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 Realmode 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, amperometricbiosensors without disturbing the environment around the electrodes.

High Stability Operation
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).
Normally when in Potentiostat mode do NOT use High Stability 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 (> 1 V/s), or whenshort term pulses (< 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 operation can be used routinely when performing fixed
potential experiments with amperometric sensors where the responsetime of the sensor is relatively slow (> 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 forany internal offset error on the current signal. This is only required forvery 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 theCalibrate button!
For best results allow about 10 minutes after opening powering up thee-corder before using the Calibrate function. This allows the unit towarm up — ambient temperature variation of more than a few degrees
during an experiment may require periodic recalibration to maintainmaximum accuracy.
When calibrating in ZRA mode you must first remove the Input
Connector (Electrode connector) from the Potentiostat.

Chapter 2 — The Potentiostat

19

When in Potentiostat mode clicking the Calibrate button will zero thecurrent signal, using the Dummy cell, including any signal due to any
small offset from the e-corder Output at E In. Thus it should beconsidered a ‘relative zero’.
Recalibatrion is required after you:• select a different range for the Potentiostat applied potential,
page 21;• turn iR Compensation on or off, page 20.
• change from Potentiostat to ZRA operating mode;• change from ZRA to Potentiostat operating mode. However, to gettrue absolute current measurements in Potentiostat mode
(independent of small offsets at E In) first calibrate in ZRA mode andthen 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 CompensationiR 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 theapplied potential to a value where no Faradaic process occurs, use thebuttons 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. Thisapplies a small perturbation (1 Hz, 10 mV amplitude square wave) tothe electrode. The 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 theselected gain range, page 99.

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 thepotentiostat will go into oscillation at some point. To avoid thishappening it is usual to always slightly undercompensate, that is, tofind the point of ideal compensation and then to reduce the setting
slightly. The amount of ‘undercompensation’ is usually determined bytrial and error for a particular experiment.
Before using iR Compensation you should always consider othermethods 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 thebackground electrolyte concentration be increased? Also check toensure that the reference electrode is not clogged or dried out. It isalways best to minimize cell resistance within the reaction chamberrather than trying to overcome the problem later with the potentiostat.

Applied Potential
The Applied Potential controls are enabled when either the Dummy orReal 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 Applied Current controls appear when in Galvanostat mode
(replacing the Applied Potential controls), see Figure 5–17, page 74.
The controls are enabled when either the Dummy or Real cell isselected. Use them to adjust the current applied, Figure 5–19,
page 75.
On Windows computers, thebutton advises on the correct values tobe entered into Units Conversion of the current signal channel, see
Figure 5–18, page 74.

Chapter 2 — The Potentiostat

21

RangeWhen 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 therange over which the applied current can be set, Figure 5–17,
page 74.
On a Macintosh computer use the values in Range control are affectedby the selection in the Stimulator Constant Output dialog box, Figure
5–8, page 64. and Table 5–1, page 77.

Remember Potential
Check thebox to remember the value of theapplied 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 63).

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, I, is in accordance with Ohm’slaw:
I = E/R
where R is the resistance, and is 1 MΩ for the dummy cell. Thus asignal of 1 µA should be obtained when a potential of 1 V is applied,
1 µA 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 tocheck the electrode cables by attaching them to a resistor (usually aresistor of 103–108 Ω 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 likelythat the electrode leads have become damaged.
However, if both the Dummy Cell and Real Cell tests produce theexpected results, but you are still experiencing difficulties with yourexperiments, then check the electrodes (reference electrodes, inparticular, tend to become clogged or dry out with age), and thedesign and condition of the reaction vessel, and any salt bridges thatyou are using.

Chapter 2 — The Potentiostat

23

24

eDAQ PotentiostatsC H A P T E R

3 The Picostat

T H R E E

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 indamage 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 areearthed before touching the Picostat input connector, connecting thelead wires, or before you connect the lead wire alligator clips to theelectrodes. You can do this (after first connecting the Picostat ande-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

The Front Panel
The front panel of the Picostat is shown in Figure 3–1.

Input Connector
The Input connector of the Picostat provides connection pins for theWorking, Auxiliary and Reference electrodes. The connector also
provides connections for shields which protect the signals in the cablewiring from electrical interference (noise pickup).
The pin assignments of the Picostat Input 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.

Figure 3–1
The Picostat front panel.
Overload
indicator light

Input connector,
6 pin Lemo socket,
to electrodes

Overload

Picostat

Online indicator light

Alignment dot

Figure 3–2
The Picostat input
connector as seen whenlooking at the front
panel.

Working Electrode

Working Electrode Shield

Auxiliary ElectrodeNot connected

Reference Electrode
Reference Electrode Shield

26

eDAQ Potentiostats

Table 3–1
Color-coding on theleads of the electrodecable.

Color

Electrode

Yellow

Reference

Green

Working

Red

Auxiliary

Electrode Cable
The Picostat is supplied with a three lead electrode cable, with eachlead terminated by an alligator clip. The Reference and Working
electrode leads are shielded to protect the signals from externalinterference. The alligator clips allow connection to a wide variety ofelectrodes. The leads are color-coded to indicate the type of electrodeto which they should be attached (Table 3–1).
For normal three-electrode use, the reference electrode must never beconnected 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 referenceelectrode leads (red and yellow) can be attached to the single ‘counterelectrode’. 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 Input
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 91.
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 goneout of compliance, which usually occurs because of an open circuit(such as an unconnected or faulty electrode) or the resistance is toohigh 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 thecompliance potential (that is, the potential between the auxiliary andworking electrodes). If the compliance voltage exceeds specification,
about 13 V, potential control of the cell is lost and drifting, oroscillation, of the signal can be seen. Any data collected during thisperiod 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 toconsider 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
channel. This is, in turn, due to a low resistance between the electrodes.

28

eDAQ Potentiostats

Figure 3–3
The Picostat back panel.

BNC output
connectors
E Out

BNC input
connector

I Out

E In

4 mm socket,
ground connection

2

Input

I C
Bus

OutputDB-9 pin, I2C connectors

The Back Panel
The back panel of the Picostat is shown in Figure 3–3.

E Out, I Out and E In Connectors
The Picostat back panel has three BNC connectors labelled E Out,I 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 thePicostat 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 theworking and auxiliary electrodes.
For most situations I Out is connected to e-corder input channel 1, andE Out to e-corder input channel 2. However, when you are using Chart
software and recording data from various sources on more that just twochannels you may want to connect the Picostat to other e-corder input
channels.

I2C Connectors
The Picostat back panel, Figure 3–3, has two DB-9 pin ‘I2C bus’
connectors labelled Input and Output. The Input connector provides

Chapter 3 — The Picostat

29

INT

DSD

SDA

DSC

I2C control signals

SCL

Regulated +17 V DC

Regulated +8 V DC

Digital Ground

Regulated –17 V DC

Power lines
Regulated –17 V DC
Digital Ground

INT
DSD
SDA
DSC
SCL

▲ WARNING!
The I2C connectors arefor the power andcontrol of eDAQ
Amps, page 2, andshould not be used forconnection to any
other device.

Regulated +17 V DC
Regulated +8 V DC

I2C control signals

Figure 3–4
The pin assignments for
the Input I2C DB-9
connectors.

1

5

5

1

6

9

9

6

Input

Outputpower 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 I2C connector can be found in youre-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 theelectrochemical cell is located, to a more sophisticated copper meshenclosure or sheet-metal box.
In all cases, it is essential that the Faraday cage be electricallygrounded to act as an effective shield against electrical interference.
The Picostat is supplied with a green colored ground cable terminatedwith a 4 mm pin (attaches to Picostat back panel) and an alligator clip(for attachment to Faraday cage) for this purpose. The Picostat itself isgrounded via its connection to the e-corder unit which is in turn earthed

30

eDAQ Potentiostatsvia the three pin mains power connector. It is of course important thatthe power socket that you are using is well earthed.
The purpose of this ground cable to the Faraday cage is to provide aneasy means of grounding the cage — please note that it is not forgrounding the Picostat. If your Faraday cage is already earthed by its
own ground connection then you should not use this cable! Use of thecable 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 bothmethods simultaneously.

Connecting the Picostat
Your Picostat will have been supplied with an I2C cable (DB–9 pin
connectors at either end), and three cables with BNC connectors ateither end.
First make sure that the e-corder is turned off. Then connect the I2C
cable to the I2C connector on the back panel of the e-corder, and theother the other end to the I2C Input connector on the back panel of thePicostat. Use the three BNC cables to connect the back panel of thePicostat to the front panel of the e-corder as in Table 3–2.

Table 3–2
Picostat to e-corder BNC
connections.

Table 3–3
Picostat to e-corder BNC
connections, reverse
polarity.

Chapter 3 — The Picostat

Picostat rear panel

e-corder front panel

I Out

Input 1E Out

Input 2

E In

Output –Picostat rear panel

e-corder front panel

I Out

Input 1E Out

Input 2

E In

Output +31

Figure 3–5
The Picostat shown
connected to an
e-corder, front view.

Overload

Picostat

Input 1401

Input 2

Input 3

Power
Status

OutputInput 4

Trigger

Figure 3–6
The Picostat shown
connected to an
e-corder, back view.

With these connections, when you use the software to set a morepositive voltage, a more oxidising potential will be applied at theworking electrode. Such an arrangement is shown in Figure 3–5 andFigure 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 morepositive voltage, a more reducing potential will be applied at theworking electrode.

32

eDAQ PotentiostatsCheck that all connectors are firmly attached. Loose connectors cancause erratic behaviour, or may cause the Picostat to fail to work.
The Picostat uses two e-corder input channels during normal operation.
The remainder of this chapter assumes that you have connected thecurrent signal to e-corder Input Channel 1 and the potential signal toe-corder Input Channel 2. (It is possible when using Chart or Scope
software to connect the Picostat to other e-corder input channels inwhich case the description that follows would change accordingly).
When using EChem software, Channel 1 is always set to be the current
signal (the I channel), and Channel 2 is automatically set to be thepotential signal (the E channel). Thus when using EChem software you
must always connect the current signal (I Out) to Input Channel 1, andthe potential signal (E Out) to Input Channel 2, of the e-corder.
Channel 2 normally displays the applied potential and its settings arecontrolled using the standard Input Amplifier dialog box, described in
the Chart and Scope Software Manuals on the eDAQ Installer CD.

First Use
After you have installed the software, connected the e-corder andcomputer as described in the booklet that is supplied with the e-cordersystem, and connected the Picostat as described above, you are readyto 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-corder (to discharge any static charge that you may haveaccumulated), then attach the 100 MΩ test resistor (supplied with thePicostat) to the electrode leads so that the Working electrode lead isconnected to one end of the resistor, and Reference and Auxiliaryelectrode 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

Chapter 3 — The Picostat

33

Figure 3–7
Accessing the Picostat
controls with Chart
software (Windows).

Current signal Drag ticks and labels
display area to adjust axis scaling

Start/stop scrolling
Select input
range
Select lowpass filter
Set mainsfilterInvert signal
Select Realor Standby
mode

Select Picostat fromthe Channel 1
Function pop-up
menu

Select range for Remember applied
applied potential potential

Figure 3–8
Accessing the Picostat
controls with Chart
software (Macintosh).

Slider bar for setting Enter applied
applied potential
potential as text

Select Picostat from the Channel 1
Function pop-up menu

Drag ticks andlabels to adjust axis

Select input
range
Select lowpass filter
Select Realor Standby
mode

Current signal
display area

Enter
AppliedPotential
Slider bar
for setting
appliedpotential

Pause/Resume
scrolling

34

Axis expansion/
contraction

Invert signal

Set mains filter

eDAQ Potentiostatsmenu says ‘Input Amplifier’ instead of ‘Picostat’ then the software has
not recognised the Picostat. Exit the software, check all yourconnections 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 thatno 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 yoursignal amplitude, and to select the 10 Hz low-pass filter (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 byentering the exact potential with text entry. The resulting current signal
should obey Ohm’s law:
I = E/R

Figure 3–9
Accessing the Picostat
controls with Scope
software.

Use the Picostat button
Pause/Resume
scrolling

Select input
range

Select lowpass filter
Signal display area

Set
AppliedPotential
Set mainsfilterDrag ticks andlabels to adjust axis

Chapter 3 — The Picostat

Axis expansion/
contraction

Select cell
mode

Invert signal

35

so that with the 100 MΩ test resistor, R, in place, an applied potential,
E, of 1 V should produce a current, I, of 10 nA, while other potential
settings should produce corresponding currents.

Picostat Control Window
With Chart software, the Picostat Control window is accessed from thePicostat 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. Notethat the signal is not being recorded to hard disk at this stage, and thatwhen the window is closed the signal trace is lost.
You can stop/start the signal scrolling by clicking the Pause/Resume
button.
You can shift or stretch the vertical Amplitude axis to make the best useof the available display area. All changes to axis scaling are reflectedin the Chart and Scope main window, and vice versa.

Setting the Range
The Range pop-up menu lets you select the input current range orsensitivity. The Picostat has ranges of 10 pA to 100 nA (if you require asystem 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 thedata will be truncated and therefore lost.

36

eDAQ Potentiostats

Filtering
The Picostat has an internal 10 Hz low-pass filter for removal of highfrequency signals (‘noise’). The Off setting gives the full bandwidth of
the Picostat which can be up to 16 kHz (but which may also be limitedby 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, should be employedwhenever 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 thesignal 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. Notethat 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, themains filter does take a few seconds to ‘learn’ the pattern of theinterference so that you will need to record for longer than this for it totake full effect. The mains filter can be employed even for experiments
in which there are sudden potential jumps.

Inverting the Signal
The Invert checkbox allows you to invert the incoming current signal. It
provides a simple way to redefine the directions (up or down) of ananodic (or cathodic) current signal. This control does not affect thedirection of current flow at the electrodes.

Cell Control
The Picostat can be in one of two operating modes, controlled by the
Cell radio buttons:• Standby: If Standby mode is selected the auxiliary and referenceelectrodes are isolated by an internal relay which effectively meansthat 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 andthe Chart, Scope or EChem Start button is clicked to begin a scan.
The Applied Potential control is disabled in this mode.
• 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 fromamperometric biosensors or in vivo electrodes without disturbing theenvironment around the electrodes.

Applied Potential
The applied potential slider control is only enabled in Real mode. It
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 controls 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
When using Chart software on a Windows computer you have theoption 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 theapplied potential.
On a Macintosh computer use the range control in the Stimulator
Constant Output dialog box, Figure 5–8.

Remember Potential
When using Chart software on a Windows computer you can select thecheckbox labelled ‘Set applied potential as baseline…’ This causes thepotential set with the slider bar or text entry to be transferred to the
Stimulator baseline control when the window is closed.

38

eDAQ Potentiostats

MaintenanceYour 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 acouple of seconds the resulting current signal should have stabilised
and be close to zero. If the current signal is drifting significantly, or isgreater than ±5 pA, then contact your eDAQ representative — it ispossible that stray static discharge may have damaged the Picostat’s
electrometer chip.
Also periodically repeat this procedure with the electrode cableconnected, and attached to the 100 MΩ 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 thee-corder, page 31. If the problem persists then it is possible that theelectrode leads or the Picostat itself has become damaged.
If these tests indicate that the Picostat is working correctly, but you arestill experiencing difficulties with your experiments, then you should
now check the electrodes you are using, the connections to them, andthe design and condition of the reaction vessel, and any salt bridges
that you are using.

Chapter 3 — The Picostat

39

40

eDAQ PotentiostatsC H A P T E R

F O U R

4 The QuadStat

This chapter describes how to connect and use your QuadStat (EA164).
Note that when used with EChem software only a single QuadStatchannel can be used. With Scope software one or two channels can beused. 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 indamage to 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 youare earthed before touching the QuadStat input connector, connecting
the lead wires, or before you connect the lead wire alligator clips to theelectrodes. You can do this (after first connecting the QuadStat ande-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 Potentiostats41

Working Electrode connectors, BNC

Figure 4–1
The QuadStat front panel

QuadStat

Channel 1

164

Channel 2
WE

WE

AE

AE

RE

Auxiliary Electrodeconnector, 4 mm socket

Channel 3

Channel 4

AE

AE

RE

Reference Electrodeconnector, BNC

WE

WE

RE

RE

Onlineindicator
light

Overload
indicator
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 eachlead terminated by an alligator clip which allows connection to a wide
variety of electrodes.The leads are color-coded to indicate the type ofelectrode 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 tominimize lead capacitance.
If two-electrode operation is required the auxiliary and referenceelectrode leads (red and yellow) can be attached to the single ‘counterelectrode’.

42eDAQ Potentiostats

Table 4–1
Color-coding on theleads of the electrodecables.

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 (suchas EChem, Chart or Scope) has located and initialised that QuadStatchannel. 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, pleaserefer to Appendix B Troubleshooting, page 91.

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 ofcompliance because of an open circuit (such as an unconnected or
faulty electrode), or the resistance is too high in the electrochemical cell.
High resistances can be often be encountered when electrodes arefouled by the products of electrolysis reactions. The QuadStat tries tocompensate by increasing the compliance potential (that is, thepotential between the auxiliary and working electrodes). If thecompliance voltage exceeds specification, about 11 V, potential controlof the cell is lost and drifting, or oscillation, of the signal can be seen.
Any data collected during this period is unreliable and should bediscarded.
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

experimental conditions to avoid fouling of the electrodes. Redesigning
your electrochemical cell may be necessary. Normally electrochemicalcells are designed to keep the reference and working electrodes very
close together, however, when a potential overload occurs, you alsoneed to consider the distance between the auxiliary and working
electrodes.

Figure 4–2
The QuadStat backpanel.

4 mm socket,
ground connection

Made in Australia by eDAQ Pty Ltd.
No user serviceable parts inside.
Refer servicing to qualified service personnel.

I Out

COM

E Out

COM

E In

Channel 1
I Out

COM

E Out

COM

E In

Channel 2
I Out

COM

E Out

COM

E In

Channel 3
I Out

COM

E Out

COM

E In

Channel 42Output1

5

DB-9 pin, I2C connectors

20

I Out

COM

E Out

COM

Channel 1
E In

E Out

COM

E In

Channel 2
I Out

COM

E Out

COM

E In

15

20-pin socket for screw
terminal adaptor, Figure 4–3.
Input and output signals
Channel 3

I Out

COM

E Out

COM

E In

Channel 4

10

I Out

I C
Bus

COM

Input

Figure 4–3
The 20-pin screw
terminal adaptor.

20-pin terminal adaptor.
Push firmly into socket

44

eDAQ Potentiostats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
channel. This is, in turn, due to a low resistance between the electrodes.
In some circumstances a current overload can also cause the 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 QuadStatchannel (Channels 1 – 4).

I2C Connectors

INT

DSD

SDA

DSC

SCL

Regulated +8 V DC

I2C control signals

1

5

5

1

6

9

9

6

Input

Chapter 4 — The QuadStat

Regulated –17 V DC

INT
DSD
SDA
DSC
SCL

Figure 4–4
The I2C connectors.

Power lines
Digital GroundI2C control signals

Regulated +17 V DC

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
Regulated –17 V DC
Digital Ground

The I2C connectors arefor the power andcontrol of eDAQ
Amps, page 2, andshould not be used forconnection to any
other device.

Regulated +17 V DC
Regulated +8 V DC

▲ WARNING!

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 I Out, E Out, or E In
signal.

Output45

range and filter selection) to and from the e-corder connection. A cableis provided with the QuadStat for this purpose. The pin assignments areshown in Figure 4–4.
The Output connector can be used for the attachment of another
QuadStat, or other eDAQ Amp.
More information about the I2C connector can be found in youre-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 theelectrochemical cell is located, to a more sophisticated copper meshenclosure 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 isalso important that the power socket that you are using is well earthed.
You can try grounding the Faraday cage via its own connection toearth, or via the QuadStat ground cable — but not by both methods
simultaneously. The purpose of this ground cable to the Faraday cage isto provide an easy means of grounding the cage — please note that it
is not for grounding the QuadStat itself. If your Faraday cage is alreadyearthed by its own ground connection then you should not use the
QuadStat ground cable! Use of the QuadStat cable in this instance will
provide a second pathway to earth which could result in a ‘groundloop’ which can actually increase signal interference!
The grounding connector is equivalent to the COM pins of the 20 pin
terminal socket, Figure 4–2.

46

eDAQ PotentiostatsConnecting the QuadStat
Your QuadStat will have been supplied with an I2C cable (DB–9 pin
connectors at either end), and nine cables with BNC connectors at one
end and bare wires at the other.

Channel 4

Channel 3

Channel 2

Channel 1

E In
COM
E Out
COM
I Out
E In
COM
E Out
COM
I Out
E In
COM
E Out
COM
I Out
E In
COM
E Out
COM
I Out

Figure 4–5
Signal connections fromthe terminal adaptor.
Black colored wires areconnected to COM pins.

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.

Channel 1
I Out
E In
COM
E Out
COM
I Out

Figure 4–6
Using the external inputsof the QuadStat. Noteconnection to E In is only
required for potentials of
more than ±2.5 V, or forpulsed or ramped
waveforms.

Single channel operation
To e-corder Input:

2

1

To e-corder Output or
waveform generator

Channel 3

Channel 2

Channel 1

E In
COM
E Out
COM
I Out
E In
COM
E Out
COM
I Out
E In
COM
E Out
COM
I Out
E In
COM
E Out
COM
I Out

Channel 4

To e-corder Input:

8

7

6

Multiple channel operation with the same
applied waveform on each channel

Chapter 4 — The QuadStat

5

4

3

2

1

To e-corder Output or
waveform generator

47

Table 4–2
QuadStat to e-corder
BNC connections. See
Figure 4–7 for actual
appearance.

QuadStat rear panel

e-corder front panel

I Out (Ch 1, Ch 2, Ch 3, Ch 4)

Input 1, 3, 5, 7

E Out (Ch 1, Ch 2, Ch 3, Ch 4)*

Input 2, 4, 6, 8

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 reverse the polarity of the QuadStat.

First make sure that the e-corder is turned off. Then connect the I2C
cable to the I2C connector on the back panel of the e-corder, and theother the other end to the I2C 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 andreference electrodes; and the current signal (I Out) indicating thecurrent 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 theelectrode potential required is greater than ±2.5 V, or is to be pulsedor 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, ora waveform generator, Figure 4–6. If an e-corder is used, then normallyconnect to Output –. With these connections, when you use thesoftware to set a more positive voltage, a more oxidising potential will
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 amore positive voltage, a more reducing potential will be applied at theworking electrode.

48

eDAQ Potentiostats

Figure 4–7
The QuadStat shown
connected to an
e-corder, front view,using the connections
described in Table 4–2.

QuadStat

Channel 1

Channel 2

Channel 3

Channel 4

164
AE

AE

AE

AE

RE

Input 1

RE

Input 2RE

Input 3

Input 4

Input 5

Input 6

Input 7

Input 8821
Power

Trigger

OutputStatusAuxiliary and reference
Use one, two, three, or
electrode leads fromfour working electrodes.
Channel 1. Use these when
the working electrodes are to
be used in the same reaction
vessel and a single auxiliary
and reference electrode are
required.

Note that the cable from thee-corder Output is not required forconstant potential experiments
between ±2.5 V

By linking the E In positions with short wires you can control thepotentials of all electrode potentials simultaneously, Figure 4–6.
Check that all connectors are firmly attached. Loose connectors cancause 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 inwhich case the description that follows would change accordingly).
When using EChem software, e-corder Input 1 is always set to be thecurrent signal (the I channel), and e-corder Input 2 is automatically set
to be the potential signal (the E channel). Thus when using EChemsoftware connect the QuadStat Channel 1 current signal (I Out) toe-corder Input1, and the QuadStat Channel 1 potential signal (E Out) toe-corder Input 2. Other QuadStat channels remain unconnected.

Chapter 4 — The QuadStat49

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.

First Use
After you have installed the software, connected the e-corder andcomputer, and connected the QuadStat as described above, you areready 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 4–8, Figure 4–9, or Figure 4–10.
The QuadStat control window allows you to preview the current signal
without actually recording the signal to the computer hard disk. (If themenu says ‘Input Amplifier’ instead of ‘QuadStat’ then the software has
not recognised the QuadStat. Exit the software, check all yourconnections 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 thatno current will flow through your electrodes. To connect to the QuadStat
electrode lead wires you must select Real mode. When you click
Cancel or OK the QuadStat will revert to Standby mode until recording
is started. For now, select the Dummy cell mode which connects aninternal 1 MΩ resistor between the electrodes.
You will need to adjust the gain range to 5 µA to accommodate yoursignal amplitude. If the signal is noisy select the 10 Hz low-pass filter(and/or Mains Filter).

50

eDAQ Potentiostats

You can now adjust the applied potential with the slider bar, or byentering the exact potential with text entry. The resulting current signal
should obey Ohm’s law:
I = E/Rso that with a 1 MΩ test resistance, R, an applied potential, E, of 1 V
should produce a current, I, of 1µA, while other potential settings
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 fromthe QuadStat command in the Channel Function pop-up menu. Figure
4–8 shows the control window on a Windows computer, and Figure
4–9 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
4–10.

Signal Display
The current signal is previewed scrolling across the display area. Notethat the signal is not being recorded to hard disk at this stage, and thatwhen the window is closed the signal trace is lost.
You can stop/start the signal scrolling by clicking the Pause/Resume
button.
You can shift or stretch the vertical Amplitude axis to make the best useof the available display area. All changes to axis scaling are reflectedin the Chart and Scope main window, and vice versa.

Setting the Range
The Range pop-up menu lets you select the input current range orsensitivity. 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 toencounter during your experiment. If, during the experiment the current

Chapter 4 — The QuadStat

51

Figure 4–8
Accessing the QuadStat
controls with Chart
software (Windows).

Drag ticks and labels
to adjust axis scaling

Start/stop scrolling
Select input
range
Select lowpass filter

Select QuadStat
from the Channel 1
Function pop-up
menu

Set mainsfilterSignal display
area

Invert signal
Select cell
Autozero

Applied potential
value

Figure 4–9
Accessing the QuadStat
controls with Chart
software (Macintosh).

Remember applied
potential

Slider bar for setting
applied potential

Click to manually adjust
zero offset. Control-click
for fine control

Select QuadStat from the Channel 1
Function pop-up menu

Drag ticks andlabels to adjust axis

Select input
range
Select lowpass filter
Select Realor Standby
mode

Current signal
display area

Enter
AppliedPotential
Slider bar
for setting
appliedpotential

Pause/Resume
scrolling

52

Axis expansion/
contraction

Invert signal

Set mains filter

eDAQ Potentiostats

Figure 4–10
Accessing the QuadStat
controls with Scope
software.

Use the QuadStat button
Pause/Resume
scrolling

Select input
range

Select lowpass filter
Signal display area

Set
AppliedPotential
Set mainsfilterDrag ticks andlabels to adjust axis

Axis expansion/
contraction

Select cell
mode

Invert signal

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 removalof high frequency signals (‘noise’). The Off setting gives the fullbandwidth 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, shouldbe employed whenever possible. However, low pass filters should be
used with care when performing pulse amperometric or voltammetricexperiments, 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, andChapter 4 — The QuadStat

53

voltammetric experiments should have scan rates scan rates less thanabout than 100 mV/s — otherwise excessive smoothing of the signal
may occur.
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. Notethat the mains filter is NOT a simple notch filter, and it 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 patternof the interference so that you will need to record for longer than thisfor it to take full effect. The mains filter can be even be employed forexperiments in which there are sudden potential jumps.

Inverting the Signal
The Invert checkbox allows you to invert the incoming current signal. It
provides a simple way to redefine the directions (up or down) of ananodic (or cathodic) current signal. This control does not affect thedirection 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 referenceelectrodes are isolated by an internal relay which effectively meansthat 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 andthe Chart, Scope or EChem Start button is clicked to begin a scan.
The Applied Potential control is disabled in this mode.
• Dummy: When Dummy mode is selected the QuadStat channel isconnected to the internal 1 MΩ dummy cell. You can then use theApplied Potential slider control to vary the voltage applied to thedummy cell. The QuadStat will remain connected to the dummy celleven when the QuadStat Control window is closed and Chart,
Scope or EChem is recording. This is useful for testing the QuadStat.

54

eDAQ Potentiostats• 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 willremain in Real mode when the dialog is closed — this allows you tostart and stop recording data while the electrodes remain active,
which allows periodic recording of the signal from amperometricbiosensors or in vivo electrodes without disturbing the environment
around the electrodes.

Applied Potential
The applied potential slider control adjusts the voltage (up to ±2.5 V)
applied to either the dummy cell or external electrodes. This potential,
EQ, is remembered by the QuadStat and will be applied when you starta scan if the “Set applied potential ...” checkbox is ticked. Note thateach QuadStat channel may have a different value for EQ.
This potential value will be summed with any external input waveform,
Ew, from the E In connection on the terminal strip connector on the
QuadStat back panel. The total potential, EQ + Ew, 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 thecheckbox is NOT ticked.

Zero Offset
The Offset control can be used to ‘zero’ a background signal so that
small peaks or transient signals can be more accurately determined in
the presence of a large baseline current signal. Each QuadStat channel
can have a different amount of offset applied. The maximum amount ofoffset available is ±400 µA on ranges of 2 µA or more, and ±400 nA
on ranges of 1 µA or less.
First tick thecheckbox. Then, while the baseline current is being
monitored click the
button. It may take a few seconds to zero
the signal. Normally this will suffice to accurately zero the signal, andChapter 4 — The QuadStat

55

you can then choose a more sensitive current range setting to observe
your signals. Use the buttons to manually adjust the amount of offset
if required (use Ctrl-click for fine adjustment, or xxx-click on Macintosh)
The amount of offset is reported in the text box,
also be directly entered in this box.

. Values can

MaintenanceYour 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 4–8 or Figure 4–9. and go to
Dummy Cell mode. The current signal, I, should obeys Ohm’s law:
I = E/R
where R is the resistance, and is 106 Ω for the dummy cell, and E is theapplied potential. Thus a signal of 1 µA should be obtained when apotential of 1 V is applied. Try several different potentials and makesure an appropriate current signal is observed. Repeat this procedureon 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 50. If the current signal does not obey Ohm’s law,then first recheck your connections of the QuadStat to the e-corder,
page 47. If the problem persists then it is possible that the electrodeleads or the QuadStat itself has become damaged.
If these tests indicate that the QuadStat is working correctly, but you arestill experiencing difficulties with your experiments, then you should
now check the electrodes you are using, the connections to them, andthe design and condition of the reaction vessel, and any salt bridges
that you are using.

56

eDAQ PotentiostatsC H A P T E R

5 Techniques

F I V EThe 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 on the computer hard disk, with the software, or can befound on the eDAQ Installer CD).
Also discussed is the use of the Potentiostat when configured as agalvanostat.
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 theoptional EChem software — see the EChem Software Manual, or
contact eDAQ for more details.

eDAQ Potentiostats

57

Introduction
The Potentiostat, Picostat, and Quadstat apply a potential difference
across a pair of working and reference electrodes whilst monitoring thecurrent flow between the working and auxiliary electrodes.
NOTE
The QuadStat also hasinternal potential
adjustment of ±2 V.
When the e-corder
output is connected toa QuadStat channel‘E in’, this value issummed with the value
set by the Chart or
Scope Stimulator
controls, to a maximumof ±10 V.

This potential difference is determined by a ‘command voltage’ which issent 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 thatcan be produced, you should consult the Chart Software Manual andScope 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 59 — 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 thePicostat and QuadStat are sufficient for scan rates up to about
10 V/s• Chronoamperometry page 61 & page 70, Amperometry,
Constant Potential Electrolysis, page 78, — monitor the current
signal at fixed potentials• Chronocoulometry page 71 — monitor and integrate the current
signal at a fixed potentials• Chronopotentiometry page 73, Constant Current Electrolysis
page 79 — monitor the potential signal when the Potentiostat isused as a galvanostat to maintain a constant current at the working
electrode. Note that the Picostat and QuadStat cannot be used asgalvanostats• Monitoring of amperometric sensors page 80, including dissolved
oxygen and nitric oxide electrodes.
• zero resistance ammeter, or high impedance voltmeter, with the
Potentiostat, page 15.

58

eDAQ PotentiostatsLinear Scan Techniques
Linear sweep or cyclic voltammetry are usually best performed with
EChem software. However, Scope also incorporates Stimulator… andOutput Voltage… commands which can be used to control the analog
output of the e-corder to create a waveform suitable for thesetechniques (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 & 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 apotential ramp has been set up to go from –1.00 to +1.00 V and backagain over a period of 40 ms using the Up & 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 thepotential limits, while the Up & Down waveform option starts a scan atone, 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

59

Figure 5–1
Scope Setup menu.

Use the Stimulator… command to access the
Stimulator (applied potential waveform) controls

Use the Output Voltage… command
to set the baseline potential

Figure 5–2
Using the Scope
Stimulator Up and Down
command.

Figure 5–3
Using the Scope
Stimulator Triangle
command.

60

eDAQ PotentiostatsThus, by setting the data acquisition rate to be as fast as possible for aparticular 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 arelooking 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 (thatis, a solution containing only the background electrolyte);
2. next a scan is performed of the solution in which the substrate ispresent; and finally
3. the Scope ‘page’ that contains the background scan is selectedusing the Display > Set Background command which will subtract
this scan from all other pages in the file. Use the Display > Don't
Subtract Background command to cancel subtraction, and Clear
Background to cancel the subtraction and clear the backgroundsweep.
The background scan must be run under the same conditions (sweep
width and stimulator settings) 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 ismaintained for a defined period while the current is monitored. If thecurrent signal is integrated with respect to time then the total chargetransferred at the electrode can be calculated (Chronocoulometry,page 71).
Single, double and even multi-step chronoamperometry, can be
performed with Chart or Scope software, in a time frame from amillisecond to hours, or even days, if need be. For experiments
involving sudden changes in potential you should use the full bandwidthof 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

61

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 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 then applies this potential across the reference andworking 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;
4. 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 becollected per second) to an appropriate value — you will usuallyrequire at least several hundred data points over the lifetime of yourexperiment. 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 witha precision better than 1 ms. Pulses up to 30 s long may be created bythis method. For further details on using the Stimulator in Chart refer tothe Chart Software Manual. An example using the Chart Stimulator isshown in Figure 5–6. Note that the pulse amplitudes are added to any
value set by the Baseline control.

62

eDAQ Potentiostats

Figure 5–4
Chart Setup menu(Windows).

Use the Stimulator command to access the Stimulator(applied potential waveform) controls, Figure 5–5 &Figure 5–6

Select stimulator mode

Figure 5–5
Chart Stimulator(waveform output)
controls (Windows).
Select output range
Enter exact values as text.
Use zero amplitude forconstant output
Baseline control canbe used for constant
output — drag slider
controls to adjust
value

Figure 5–6
Stimulator controls for
multiple step
chronoamperometry(Windows).

Settings to produce a 500
mV amplitude 1 Hz squarewave, on a base potentialof –200 mV

Potential waveform generated by
the Stimulator settings above

Chapter 5 — Techniques

63

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 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 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.

Figure 5–7
Chart Setup menu
(Macintosh).

Use the Stimulator command to access the
Stimulator (applied potential waveform) controls

Use the Output Voltage… command to
set the baseline potential, Figure 5–8

Figure 5–8
Chart Stimulator
Constant Output voltage
controls (Macintosh).
Select output
range

64

eDAQ Potentiostats

To adjust the potential you will first need to select the range bychoosing the Output Voltage command in the Setup menu to activate
the Stimulator Constant Output dialog box, Figure 5–8. The smaller theselected 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 anoxidation/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 thecurrent 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 model of computer andwhat else is happening in the computer operating system. For accurate
timing it is better to use the Chart Stimulator which is fully under thecontrol of the internal e-corder clock.

Figure 5–9
Adjusting potential with
the Chart Timed Events
feature. (Macintosh only)

Access Timed Eventsfrom the Setup menu

Chapter 5 — Techniques

Changing the potential
after a period of 30 s

65Figure 5–10
Simulator controls for
multiple step
chronoamperometry(Macintosh).

Using the Stimulator command (Setup menu) it is possible to send andmonitor 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.

Stimulator settings to
produce a 500 mV high,
0.5 Hz square wave

Potential waveform generated bythese 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)
nFAC Di = -----------------------1000 πt
It is usually easier to first simplify the Cottrell equation thus:ai = ----twhere a is treated as an empirical constant to be determined.

66

eDAQ Potentiostats

Figure 5–11
Typicalchronoamperometricdata, analyzed using theArithmetic channel
calculation and the X–Y
window.

Typical experiment with1/√t data calculated on
Channel 3 using theArithmetic channel

Region of ideal linear
response
Cottrell graph of current versus
1/√t prepared in the XY
Window. Deviations fromlinearity typically occur at verysmall 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 plot the current signal (usually on
Channel 1) versus Channel 3, and a near straight line should beobtained with a slope of a, Figure 5–11.
With the Curve Fit extension installed, you can use the Curve Fittingcommand (Windows menu) to fit your current signal data with an
Chapter 5 — Techniques

67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 toconvection currents in the vessel causing non-ideal diffusion) so a small
non-zero constant, b, is added. Also the equation is very sensitive to theexact instant when t is 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=0 at start of block’ option as shown in Figure 5–12).
In this case, to get a well behaved equation when the data selectedstart 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 willtake a small amount of time to register a true value after a suddenchange in potential).
Thus a better form of the equation to be fitted is:ai = -------------- + b
t+cThis must be entered as a New Equation in the Curve Fit extension thevery 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 valuesof a and b. Some trial and error will be involved while you makeguesses 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 atvery long times when convection aided diffusion will produce non-ideal
behaviour. The exact time period that is suitable will depend on thesize of the electrode, and some trial and error to determine the timeinterval 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
68

eDAQ Potentiostats

Figure 5–12
Fitting a Cottrell equation
to data with the Curve Fit
extension.

At the time of writing theCurve Fit extension is
only available for Chartfor Macintosh.

Define the Cottrell
relationship as a newequationFirst lock in a value for c, thentry guesses for a and b until anapproximate fit is obtained

Usually use ‘t=0
at start of block’

Iterate by clicking the Fit button, refining a
and b only. If the initial guesses are closeenough, then a curve of better fit with newvales for a and b will be obtained.

Unlock c, and iterate again. A curveof best fit should be obtained.

Chapter 5 — Techniques

69and the Curve Fit extension are installed.
Remember to operate the Potentiostat or Picostat at full bandwidth (thatis 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 programof 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
Stimulator (applied potential waveform) controls

Figure 5–13
Scope controls for
multiple step
chronoamperometry.
Use the Output
Voltage…
command to set thebaseline potential

Adjust the pulse
waveform
duration,
amplitude andfrequency

70

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 forwhich it will be applied) is set using the Stimulator command. In theexample shown in Figure 5–13, after a period of 10 s at the basepotential of +0.5 V, two 30 s pulses of –0.70 V are to be applied eachfollowed 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’ datasubtracted with the Set Background command. You can then copy andpaste the scan to a spreadsheet so that the differences can be plottedagainst 1/√t 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 the total chargetransferred (the total number of coulombs, or electrons, transferred) is
equal to the integrated current, the settings used forchronoamperometry, page 61, 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 toobtain the integral. To configure Channel 3 you need to choose theComputed 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

71

Figure 5–14
Online integration of thecurrent signal using
Chart Computed Input
integration (Windows).

Figure 5–15
Online integration of thecurrent signal using
Chart Computed Input
integration (Macintosh).

Figure 5–16
Integration of the current
signal using Scope
Computed Functions.

Select Integrate in the Function menu

72

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 torecalculate the integral from the original current 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 thisbeforehand. A good strategy is often to use the real time integral
function to get an idea of what is happening during an experiment andthe use post-acquisition integration to prepare data for a final report.
With Scope software the current signal can be integrated by using theComputed Functions… command, Figure 5–16. The Integrate item ischosen from the Function menu. This is actually a post-acquisition
function — you can always cancel it afterwards to look at theunderlying 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 willremain approximately constant until the electroactive species isconsumed, 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 (I)’ cable of the Potentiostat is connected to
Input 1 of the e-corder, and the ‘CH2 (E)’ cable of the Potentiostat isconnected to Input 2.
Note that galvanostat mode is not available with the Picostat or
QuadStat.
When using the Potentiostat as a galvanostat, the applied current canbe 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 µA is required then a range setting of
1 mA (1000 µA) should be used, and then exact current value adjusted
accordingly.

Chapter 5 — Techniques

73

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 isalways a small amount of offset (error) in the system. If you are trying tomeasure 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.

Figure 5–17
Setting up the
Potentiostat as a
Galvanostat (Windows).

SelectPotentiostat in
the Channel
menu

Potential signal is displayedwhen in Galvanostat mode
Select the expected range
for the potential signal

Selectgalvanostat
operation

Access Current channel units
conversion dialog, Figure 5–18

Figure 5–18
The Current channel units
conversion dialog box.

74

Set applied current

Use these values to set
Units Conversion for
the Current channeleDAQ Potentiostats

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 bereversed 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 Conversionof Channel 2 so as to ensure that the current signal is recorded in thecorrect current units, Figure 5–18.
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 5–19.
Always select an appropriate current range for your system. While it ispossible 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.

Figure 5–19
The Chart Stimulator
dialog box when the
Potentiostat is in
Galvanostat mode

When in Galvanostat
mode the Stimulator
controls are used toadjust the appliedcurrent.Compare withPotentiostat mode where
the Stimulator is used toadjust applied potential,
Figure 5–6.

Chapter 5 — Techniques

75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 requirevery small currents always use 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 bereversed from normal (potentiostatic) operation. That is, the ‘I Out’Figure 5–20
Setting up the
Potentiostat as a
Galvanostat (Macintosh).

Select Potentiostat in
the Channel menu
Select the expected range
for the potential signal

Select galvanostat
operation

Potential signal isdisplayed when in
Galvanostat modeSetappliedcurrent

The four Galvanostat current range settings inthis menu, are dependent on the e-corder
Output Voltage range, Table 5–1

76

eDAQ Potentiostats

Table 5–1
Galvanostat current
range settings of the
Potentiostat as a functionof e-corder output range.

Galvanostat Current Ranges
e-corder Output
Range

Potentiostat/Galvanostat primary gain
100 nA/V

1 µA/V

10 µA/V

100 µA/V

1 mA/V

10 mA/V

10 V

1 µA

10 µA

100 µA

1 mA

10 mA

100 mA

5V

500 nA

5 µA

50 µA

500 µA

5 mA

50 mA

2V

200 nA

2 µA

20 µA

200 µA

2 mA

20 mA

1V

100 nA

1 µA *

10 µA *

100 µA *1 mA *

10 mA *

500 mV

50 nA

500 nA *5 µA *

50 µA *

500 µA *5 mA *

200 mV

20 nA

200 nA *2 µA *

20 µA *

200 µA *2 mA ** Usually it is better to use corresponding settings 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 105 Ωinternal dummy cell). Try selecting a more appropriate 1 µA or 10 µA
range, where the offset will be correspondingly smaller, and 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 64. 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 thelargest 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 — Techniques77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 µA, Table 5–1,
you might now wish to do an experiment where the current is held at aconstant 35 µA (or 35/50 × 100 = 70% of the range setting). You
should now set the slider control of the Output Voltage control to avalue 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 the 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 issimilar to using Chart software (Macintosh version), see page 76.
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 61, and is also known as amperometry. A constantpotential is applied at the working electrode which is sufficient tooxidize or reduce the substrate. As the electrolysis continues thesubstrate 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 forchronoamperometry. The integrated current (that is, the total chargetransferred) can also be determined by integrating the current signal(see Chronocoulometry, page 71) and this can be used to determine
the extent of reaction.

78

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 thetechnique may be referred to as electrosynthesis rather thanchronoamperometry.
If the reaction causes the formation of a polymer film on the electrode(for example pyrrole to polypyrrole, or aniline to polyaniline) then thetechnique 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 thehalf-wave potential in order to ensure complete reaction. It is usuallyimportant to separate the auxiliary (counter) electrode from the main
body of the electrochemical cell by means of a salt bridge. This is toprevent the reduction products formed in the region of the auxiliaryelectrode reacting with the products of oxidation at the working
electrode (or, if reducing the substrate, to prevent the products ofoxidation forming around the auxiliary electrode from reacting with the
reduction products at the working electrode). The working electrode isusually constructed to have relatively large surface area so that agreater amount of material can be electrolyzed in a small time — thus aplate 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 (> 100 mg) in reasonable
times requires relatively high currents to be passed through the cell.
Thus the Potentiostat (maximum current 100 mA) is usually moresuitable than the Picostat (< 100 nA) or QuadStat (< 1 mA/channel) for
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 todifficulties in later separation of the product). For studies using water, orother 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 73, and require the use of a galvanostat. The Potentiostat, when

Chapter 5 — Techniques

79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 theworking and auxiliary electrodes and the potential at the working
electrode is monitored as the substrate is oxidized or reduced. As theelectrolysis continues the substrate is eventually completely consumed
and the potential will alter as the galvanostat tries to maintain aconstant current. Both the potential and the current flow can bemonitored with Chart software. The integrated current (that is, the total
charge transferred) can also be determined which can be used todetermine the extent of reaction.
Electrosynthesis and electropolymerization reactions are often more
quickly carried out under constant current conditions than underconstant 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 thecompliance voltage (10 V) of the Potentiostat/Galvanostat, at least until
the reaction of interest is complete. Electropolymerization reactions canbe problematic as a non-conducting polymer film adhering to theworking 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 threeelectrode configuration. The Potentiostat (up to 100 nA), Picostat (up to
100 nA), and QuadStat (up to 1 mA) can be used in three electrodemode (working, reference and auxiliary electrode), or in two electrodemode (working and counter electrodes) by connecting the reference
and auxiliary leads of the electrode cable together. You will also needto determine the correct ‘polarising voltage’ to use with your sensor.

80

eDAQ Potentiostats

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, eachat a different potential, all using the same reference and auxiliaryelectrode. 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.
Normally Chart software (rather than Scope) is the better choice ofrecording software for these types of sensor. The Units Conversion
feature of Chart can be used to perform two point calibration of thesignal 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 Injection Analysis extension (available on Windows
computers only) can be used to determine peak areas, prepare acalibration graph, and apply the calibration results to determine theamount of material in the unknown sample peaks. PowerChrom
software can also be used with the QuadStat and e-corder hardware asa electrochemical detector for HPLC experiments.
You can download the extensions and accompanying documentationfrom the 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 usedfor various pulse amperometric experiments. See the EChem Software
Manual for more details.

Biosensors
Biosensors are often amperometric sensors and so can be used with thePicostat, 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

81

The QuadStat also has the ability to zero (or offset) a backgroundcurrent 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 ofconcentrations. The Chart software Multiple Point Calibration extension
can be used to extend the useful range over which a biosensor can beused 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, andChart software would normally be used to record data.

Dissolved Oxygen (dO2) Sensors
Usually a polarographic (Clark) oxygen sensor electrode and meter arepurchased 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 andcan 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
polarising voltage (applied potential) of between –0.7 to –0.8 V isrequired at the working electrode to effect the reaction:+–

O 2 + 4H + 4e → 2H 2 O
The exact potential can be varied to suit the sample being measured
and to minimise side reactions. A smaller potential reduces sensitivity
but is usually more selective for oxygen.

82

eDAQ Potentiostats

Most oxygen sensors exhibit a slow response time and will take at least
several seconds to stabilise. Thus you would normally employ a1 – 10 Hz filter setting on the Potentiostat or Picostat in order tominimise 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 backgroundcurrent signal which can be of use when trying to amplify small peaks
on a large background signal, see Zero Offset, page 55.
If you intend to monitor oxygen concentrations over a wide range then
you can calibrate the electrode at several concentrations and use theChart software Multiple Point Calibration extension to compensate for anon-–linear electrode response. You can download the extension fromwww.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 auxiliaryelectrode 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:–+

NO + 2H 2 O → NO3 + 4H + 3e–

The exact potential can be varied to suit the type of electrode (manyelectrodes 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 usuallydependent on the polarising voltage, but between +0.7 and +1.0 V thecurrent signal tends to plateau as the reaction is limited by the rate at
which nitric oxide can diffuse to the anode surface. At potentials

Chapter 5 — Techniques83greater than +1.0 V the hydrolysis of water gradually becomes thedominant source of the current signal.
Most nitric oxide sensors exhibit a slow response time and will take atleast several seconds to stabilise. Thus you would normally employ a1 – 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 theChart 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 backgroundcurrent signal which can be of use when trying to amplify small peaks
on a large background signal, see Zero Offset, page 55.

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A Technical Aspects

This appendix describes various technical aspects of potentiostat
construction — you do not need to understand this material to use thePotentiostat, Picostat or QuadStat. Please note that this information is
not intended as a service manual and that user modification of theequipment 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 bysending information on a special communications connection called the‘I2C bus’ which also supplies DC power.

Potentiostat
The Potentiostat is designed to function as either a potentiostat (Chart,
Scope or EChem software) or galvanostat, ZRA (zero resistanceammeter), or high impedance voltmeter (Chart and Scope software
only). The mode of operation is under software control. A block
diagram of the Potentiostat circuitry is shown in Figure A–1.
The Potentiostat is fitted with an internal 1 MΩ dummy cell for use inpotentiostat or galvanostat mode. The dummy cell is physicallyconnected 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 I to V convertor and PGA. The maximum
current output signal (I Out) is 10 V at any gain setting. SecondaryeDAQ Potentiostats85

1 Hz Square
Wave

Front Panel
Overload
detector

Overload

Auxiliary

Error
Voltagex10
Power Amp

GroundRef Amp+

100 kΩ

+100 kΩ

E In(Commandvoltage)∑

E Out(Reference
voltage)iR Comp

Hi Z

×Shield1 MΩ
I to V

Working
Shield––Reference

Dummy
Cell

OnlinePGA
x1
x10

Back Panel

10 MΩ

DAC

Low Pass
FilterFigure A–1
Block diagram of the
Potentiostat.

I2C Control
InterfaceI Out
I2C Input
I2C Output

amplification of the current signal is done by the e-corder. The gain andsecondary amplification are set by the single ‘range’ menu in thesoftware which offers a combined total of 21 current range settingsfrom ±20 nA to ±100 mA in 1:2:5 steps, page 98.
The Potentiostat uses a differential input amplifier to compare thedifference in potential between the reference electrode and theexcitation potential set using the analog output of the e-corder. The
output of this amplifier provides an error signal the feed back circuittries to zero.
The reference and working electrode lead wires are actively shielded(that is, the shield is driven at the same potential as the lead wire itself)
to minimise electrical interference.
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.

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 isshown in Figure A–2.

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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 tominimise 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 flow in the
Working electrode is the quantity being measured.
When the Picostat is in Standby mode the Working and Referenceelectrodes 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 asmall 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.

Figure A–2
Block diagram of thePicostat.

Overload
Detector

Front Panel

Back Panel

Overload
OperatePower Amp

Auxiliary
Disconnect

Gain
Error
Voltage
Ref Amp+–

E In(Commandvoltage)

E Out(Reference
voltage)

Hi Z

Reference
ShieldSubtractor

OperateLow–pass Filter

I Out

Virtual Ground (0 V)
Working
ShieldOnlineAppendix A — Technical Aspects

I to VI2C Control
Interface

I2C Input
I2C Output

87

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, theoutput of which reads directly in current units and is also applied to thee-corder unit. The 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. 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 samepotential as the lead wire itself to minimise electrical interference, andreduce lead capacitance.

QuadStat
The QuadStat is comprised of four subunits which function in
potentiostat mode only — that is the QuadStat cannot be used as agalvanostat. A block diagram of the QuadStat construction is shown in
Figure A–3.
Front Panel

Back Panel

Overload Detector

Overload

Auxiliary
Dummy
Cell

Figure A–3
Block diagram of the
QuadStat, Channel 1.

ShieldPower Amp

Subtractor

Gain

+
–

Ref AmpError Voltage

Hi Z

Reference
I to V–

Shield

+

I Out

PGA

–

E Offset
DAC∑

OnlineE Out(Reference
voltage)+ ∑–Low–pass Filter+
Working

E In(Commandvoltage)

I OffsetDAC

I2C Input
I2C Control
InterfaceI2C Output

To QuadStat channels 2, 3, and 4

88

eDAQ PotentiostatsWithin the QuadStat an ‘error voltage’ is generated from the difference
between the voltage on the Reference electrode and the sum of theexcitation (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
which is applied to the Counter electrode (CE) in such a way as tominimise 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 theCounter Electrode (CE) voltage is controlled in such a way as to makethe 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 andallows a simple test of circuit operations.
A steady state, or transient, overload condition is indicated when theerror voltage exceeds a small non-zero value. This indicates that thesystem 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.
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.
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. The current
measured by the voltage-to-current convertor can be zeroed by meansof an offset current — this is useful in situations where a large‘background current’ is present, as might occur in a flow injection
analysis experiment, or during in vivo neurotransmitter monitoring. The
QuadStat has six gain ranges from 100 µA/V to 200 pA/V in 1:2:5
steps. The maximum current output signal (I Out) is 10 V at any gain
setting. Secondary amplification of the current signal is done by thee-corder. The gain and secondary amplification are set by the single

Appendix A — Technical Aspects

89‘range’ menu in the software which offers a combined total of elevencurrent 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 highimpedance signal) are maintained at the same potential as the leadwire itself to minimise electrical interference, and reduce leadcapacitance.
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 useof DC power allows its use inside Faraday cages.
Multiple electrode potentiostat designs for sensor work have beenreported 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.

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B Troubleshooting

B

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 Software InstallerCD.
In many cases, a problem can be fixed by turning the e-corder andcomputer off, checking connections, and starting again. Also try
performing the maintenance checks on page 22, page 39, andpage 56. If you cannot correct the problem, then please contact youreDAQ 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, 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 arecorrectly connected, see page 11, page 31, and page 48.
• 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.
• If you are using EChem software, check that the ‘E In’ cable isconnected to the e-corder output and the ‘I Out’ and ‘E Out’ cables
are connected to e-corder Input 1 and 2, see page 11, page 31,
and page 47.

eDAQ Potentiostats91• Try using the Potentiostat, Picostat, or Quadstat with anothere-corder (if available). If the Online indicator fails to light on thesecond e-corder, the Potentiostat, Picostat, or Quadstat, may be
faulty — contact eDAQ. If it works correctly on a second e-corderthen the first e-corder may be faulty — contact eDAQ.
The ‘Potentiostat’, ‘Picostat’, or ‘QuadStat’ controls cannot be accessedin Chart, Scope or EChem software (that is only the standard ‘Input
Amplifier’ dialog box of the e-corder can be accessed)• Check that the Online indicator is illuminated after the software
has been opened. If not, then proceed as in the previous problem.
• Check that you have connected the ‘E In’, ‘I Out’ and ‘E Out’cables correctly to the appropriate e-corder connectors.
The Overload indicator is on (a potential overload has occurred).
• Check that the electrode cables are firmly attached to theelectrodes.
• Check that the surfaces of the electrodes have not become fouled.
• The Picostat or QuadStat Overload indicators may come on when
the software is started — this is normal. The Overload indicator lightshould go out when you open the Picostat controls, or start
recording.
• See page 8, page 28 or page page 43 for more details.
The current signal goes off scale.
• Increase the full scale current range setting.
• Make sure each electrode is connected to the correct lead wire,
page 7, page 27, or page 43.
• Make sure the electrodes (and the alligator clips connecting themto the lead wires) are not touching each other.
• Decrease the surface area of your working electrode.
• Decrease the concentration of the background electrolyte.
• Decrease the concentration of the substrate.
• Check that a potential overload (see previous section) has notoccurred.
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eDAQ Potentiostats

The results show peaks or steps at the inverse polarity I expect to see(i.e. a peak may be occurring at 0.5 V when it should be at –0.5 V).
• Check that you are connected to the correct Output (+ or –) of thee-corder. See Connecting the Potentiostat, page 11, or Connecting
the Picostat, page 31, or Connecting the QuadStat, page 47.
• 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.
• See previous section.
• Make sure the reference electrode is connected to the correct(yellow) lead wire, page 7, page 27or page 43. Connection of thereference electrode to either the working or auxiliary leads can also
cause rapid electrode deterioration requiring electrode replacement.
• Check the condition of the reference electrode. All referenceelectrodes 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 ofsilver oxide. As this process takes place the apparent positions ofyour 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 reconverted to AgCl), although you may
wish to remove the old coating completely and re–chloridize thesilver wire to ensure a good coating of fresh AgCl. In either casereplace the newly coated wire back into the electrode casing withfreshly prepared KCl solution. Aged calomel (Hg/Hg2Cl2)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 wantthem in positive direction.
• Check that the Invert box is checked or not, as appropriate, forthe current recording channel. See Inverting the Signal on page 18,
page 37, or page 54.

Appendix B — Troubleshooting

93

The results show peaks (or steps) at different potentials than you expect.
• See previous section.
• Make sure the reference electrode is connected to the correct(yellow) lead wire!
• Check the condition of the reference electrode. All referenceelectrodes 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 ofsilver oxide. As this process takes place the apparent positions ofyour 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 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 withfreshly prepared KCl solution. Aged calomel (Hg/Hg2Cl2)electrodes should usually be replaced. Reference electrodes using agelled 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) frompower lines and mains–powered equipment. Note that, dependingon the sampling rate, aliasing can make such interference appear
as a low frequency oscillation superimposed on your data. Ensurecommon grounding by attaching the e-corder and computer to thesame power board which is then attached to a three pin (grounded)
power socket. If consistent with the bandwidth required by yourexperiment, use the 10 Hz (or lower) filter of to record your results,
see page 17, page 37, and page 53. Get an electrical technician
to check that the grounding of the power socket itself is in goodcondition. Try the Mains Filter setting (Chart and Scope software)
which is very effective at removing main induced artifacts• Check electrode connections. Poor electrical contact to theelectrodes will act as a source of noise. Particularly check theelectrode cables: cables age, especially at the alligator clips where
they are subject to mechanical wear. Use a multimeter to ensure thatthe clips are still in good electrical contact with the correct pins in

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the input connector of the electrode cable, see Figure 2–2 onpage 6, Figure 3–3 on page 29, and Figure 4–2 on page 44. Alsocheck that the shield pins have not shorted to any of the alligator
clips.
• Ensure that the reaction vessel (and electrodes) are positioned as
far as possible from power leads, computers, monitors and othermains–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 thePicostat).
• 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 beparticularly suspect. Try turning such equipment off during yourexperiment to identify the source of the problem. You may have tochange your location (try a power socket on another circuit in thesame room, or even move rooms completely).

Appendix B — Troubleshooting

95

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C

Potentiostat
Power Amp
Compliance voltage:
Output current:> 10 V±100 mA maximum

Current limit:±200 mA

Slew rate:

3 V/µsElectrometer
Input resistance:
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:
Gain accuracy:

eDAQ Potentiostats

1013 Ω

±0.8 µV/°C
0.1%

97

Current Measurement and Control
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 µA

1

±1 µA, 500, 200 nA

0.1±100, 50, 20 nA

0.01

Maximum current signal:
Low pass filters:

10 V
10 000, 1000, 100, 10 Hz
3rd order Bessel

e-corder filter settings:

10 kHz to 1 Hz in 10:5:2 steps

Gain accuracy:

0.2% at ranges 1 mA or smaller
1% at 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): 16 kHz (@ –90° lag)
160 Hz (high stability mode, @ –90° lag)
Ramp follower error:

98±1 mV @ 100 V/s±1 mV @ 1 V/s (high stability mode)eDAQ Potentiostats

iR Compensation
Current Range SettingCompensation Range±100, 50, 20 mA

0 – 10 Ω±10, 5, 2 mA

0 – 100 Ω±1 mA, 500, 200 µA

0 – 1 kΩ±100, 50, 20 µA

0 – 10 kΩ

±10, 5, 2 µA

0 – 100 kΩ

±1 µA, 500, 200 nA

0 – 1 MΩ

±100, 50, 20 nA

0 – 10 MΩ

Control PortI2C input and output:

Male and female DB-9 pin connectors.
Provides control and power to the
Potentiostat.

Power requirements:±17 V DC
+8 V DC
25 mA typical
2W

Physical Configuration
Dimensions (h × w × d):
Weight:Operating conditions:

50 × 76 × 260 mm
1.96 × 3.0 × 10.2 inches
0.8 kg (1.8 lb)
0 – 35˚C
0 – 90% humidity (non-condensing)eDAQ reserves the right to alter these specifications at any time.

Appendix C — Specifications

99

Picostat
Electrometer & Power Amp
Compliance voltage:> 13 V

Maximum control voltage:±10 V

Output current:±100 nA maximum

Input impedance:

1013 Ω || 1 pF

Input bias current:< 250 fA @ 25˚C (60 fA typical)

Current Measurement and Control
Current ranges:
Gain:
DC current error:
Filter setting:±100, 50, 20, 10, 5, 2, 1 nA
±500, 50, 20, 10 pA
10, 1, 0.1 nA/V
< ±1% FS on ranges of 10 pA – 1 nA
< ±0.5% FS on ranges of 2 – 100 nA
10 Hz low-pass. 3rd order Bessel

e-corder filter settings:

10 kHz to 1 Hz in 10:5:2 steps

Bandwidth, unfiltered:> 10 kHz, on ranges of 20 – 100 nA~ 1 kHz, on ranges of 10 pA – 10 nA

Drift with temperature:< 20 µV/˚C

Control Port100

I2C input and output:

Male and female DB-9 pin connectors.
Provides control and power to thePicostat.

Power requirements:±17 V DC, ~ 20 mA+8 V DC, ~ 20 mA~ 1 W quiescenteDAQ PotentiostatsPhysical Configuration
Dimensions (h × w × d):
Weight:Operating conditions:

50 × 76 × 260 mm
1.96 × 3.0 × 10.2 inches
0.8 kg (1.8 lb)
0 – 35˚C
0 – 90% humidity (non-condensing)eDAQ reserves the right to alter these specifications at any time.

Appendix C — Specifications

101

QuadStat
Electrometer & Power Amp
Compliance voltage:
Maximum control voltage:> 11 V±2.5 V using internal control±10 V using external input

Output current:±1 mA maximum

Input impedance:

1013 Ω || 1 pF

Input bias current:< 1 pA @ 25˚C

Current Measurement and Control
Current ranges:

I/V Gain:
I/V Multiplier:
DC current error:±1 mA±500, 200, 100, 50, 20, 10, 5, 2, 1 µA
±500, 200, 200, 50, 20, 10, 5, 2 nA100, 10, 1 nA/V
×1, ×1000< ±1% FS on ranges of 2 µA – 1 mA
< ±0.5% FS on ranges of 2 nA – 1 µA

Current signal offset:±400 µA on ranges 2 µA – 1 mA±400 nA on ranges 2 nA – 1 µA

Bandwidth, unfiltered:> 10 kHz, on ranges of 2 µA – 1 mA
~ 1 kHz, on ranges of 2 nA – 1 µA

Low pass filter:

10 Hz, 3rd order Bessel

e-corder filter settings:

10 kHz to 1 Hz in 10:5:2 steps

Drift with temperature:< 10 µV/˚C

Control Port102

I2C input and output:

Male and female DB-9 pin connectors.
Provides control and power.

Power requirements:±17 V DC, ~ 20 mA+8 V DC, ~ 20 mA~ 0.6 W quiescenteDAQ PotentiostatsPhysical Configuration
Dimensions (h × w × d):
Weight:Operating conditions:

60 × 150 × 200 mm
2.4 × 5.9 × 7.9 inches
1.5 kg (3.3 lb)
0 – 35˚C
0 – 90% humidity (non-condensing)eDAQ reserves the right to alter these specifications at any time.

Appendix C — Specifications

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D Electrochemical
EquationsD

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:i p = 269n3⁄2ai p = – 269 n

AD

3⁄2

c

1⁄2

AD

Cν

1⁄2

1⁄2

for an oxidation (anodic scan)

1⁄2

for a reduction (cathodic scan)CνThe potential where this occurs is given by:
E p = E 1⁄c20.0285– -----------------------------n

E p = E 1⁄a2

0.0285+ -----------------------------n

where
ip

a

= current peak during anodic scan (A)i p = current peak during cathodic scan (A)cE p = potential at current peak for anodic scan (V)aE p = potential at current peak for cathodic scan (V)c= half potential as determined by cyclic voltammetry (V)2n = the number of electrons transferred to (or from) the substratemolecule
A = area of the exposed surface of the electrode (cm2)

E 1⁄

eDAQ Potentiostats105

D = diffusion coefficient of the substrate molecule (cm2/s)
C = concentration of the substrate molecule (mol/L)ν = the scan rate (V/s).
The factor of 269 is a parameter that derives from using a planarelectrode at a temperature of 298 K.
Thus a truly reversible reaction can be identified by examining theadherence of the system to the following functions:
ip ∝ ν

Ep independence of the scan rate, υIn addition cyclic voltammograms will exhibit:
Ep – Epacip------aip= 1

57= -----nmV (at 298 K)c

When working in highly resistive solutions, which is often the casewhen using organic solvents for cyclic voltammetry, the referenceelectrode should be kept as close as possible to the working electrodeto minimise iR drop. Nonetheless there may still be an appreciable
uncompensated resistance which will cause E pa – E pc to become larger
than predicted, the peaks to be broader, and the peak currents to besmaller.

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Chronoamperometry
The Cottrell Equation
When chronoamperometry is performed on an unstirred solution at aplanar electrode the faradaic current response is described by the
Cottrell equation
1⁄

nFAD 2 C
i = ---------------------------------1⁄ 1⁄1000π 2 t 2
where
n = the number of electrons transferred to (or from) the substratemolecule
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/√t should produce a straight line.
In aqueous solution the coefficient of diffusion usually has a value of
between 10–5 and 10–6 cm2/s.

Appendix D – Electrochemical Equations

107

Chronocoulometry
The Integrated Cottrell Equation
The current response equation at a planar electrode for achronocoulometric experiment is the time integrated form of the Cottrell
equation:
Q =

t

1⁄

1⁄

2nFAD 2 Ct 2-+ki dt = ---------------------------------------1⁄01000π 2∫where
Q = the number coulombs transferredn = the number of electrons transferred to (or from) the substratemolecule
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 anintercept of k, which in turn can be defined as:
k = nFAΓ + Qdl
whereΓ = surface concentration of adsorbed substrate (mol/cm2)
Qdl = double layer charging.

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eDAQ PotentiostatsOverload

Picostat

Index

A

analysis 66
Chart
Macintosh 64
Windows computers 62
multiple step 63, 66, 70
Scope 70amperometric sensors 80
amperometry 57, 78
Applied Current
Potentiostat/Galvonostat 21
Applied Potential
Potentiostat 21

chronocoulometry 71, 108
chronopotentiometry 73

autozero
QuadStat 55

compliance 80

Bcurrent signal calibration
Potentiostat 19

back panel
Picostat 29
Potentiostat 9
QuadStat 45

Cottrell equation 66, 71, 107
integrated form 108

current signal zero
QuadStat 55
curve fitting 68

baseline zero
QuadStat 55

cyclic voltammetry 57, 59, 105

biosensors 81

DBridge Amp 2

Ccalibration
multiple point 81
non–linear 81
potentiostat current signal 19
two point linear 81
ZRA current signal 19
checking procedure 3
chronoamperometry 61, 107eDAQ Potentiostatsdifferential pulse voltammetry 57
dissolved oxygen sensor 82
Dummy cell
Potentiostat 18
QuadStat 54

E
E In connector
Picostat 29
Potentiostat 9
QuadStat 45
109

E Out connector
Picostat 29
Potentiostat 9
QuadStat 45

front panel
Picostat 26
Potentiostat 6
QuadStat 42

EChem software 1, 57
eDAQ Amps 2
Bridge Amp 2
GP Amp 2
pH Amp 2
Picostat 2
Potentiostat 2
QuadStat 2
eDAQ potentiostats 1

G
galvanostat 58
setting current values 73
Galvanostat mode
Potentiostat, electrode connection 7
galvanostat mode 73
Potentiostat 16

electrochemical equations 105

GP Amp 2

electrode cable
Picostat 27
Potentiostat 7
QuadStat 42

ground loop 10, 31, 46

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 79
controlled potential 78
electropolymerisation 79, 80
electrosynthesis 79, 80

FFaraday cage grounding cable 30
Potentiostat 10
Faraday's constant 107
fast cyclic voltammetry 59
fast linear sweep voltammetry 59

110

grounding cable 30
Potentiostat 10
grounding connector
Picostat 30
Potentiostat 10
QuadStat 46

Hhigh impedance voltmeter
Potentiostat 7, 16
High Stability
Potentiostat 18
High Z mode
Potentiostat 16
Potentiostat, electrode connection 7

I
I Out connector
Picostat 29
Potentiostat 9
QuadStat 45
I2C connector
Picostat 29
Potentiostat 10
QuadStat 45
input amplifier 13, 33, 50
input connector
Picostat 26
pin assignments 26
Potentiostat 6
eDAQ Potentiostatspin assignments 6
QuadStat 42
integrated Cottrell equation 108
iR Compensation 99
Potentiostat 20

Picostat 2
polarity
Picostat 32
Potentiostat 12
QuadStat 48
polyaniline 79

Llead wire capacitance 26, 42
linear scan techniques 59
linear sweep voltammetry 57, 105M
Mains Filter 94

polypyrrole 79
potential overload 80
Potentiostat 2
electrode connection 7
modes of operation 15
problems 91
pulsed amperometry 57

mains hum 94

QmaintenancePicostat 39
Potentiostat 22
QuadStat 56

QuadStat 2

microdialysis sensor 82

Randles-Sevcik equation 105

multiple step chronoamperometry 63, 66, 70

Real cell
Picostat 38
Potentiostat 18
QuadStat 55

Nnitric oxide sensor 83
noise 10, 30, 46, 94
normal pulse voltammetry 57

O
OffsetQuadStat 55
Ohm’s law 22, 35, 51, 56
Online indicator
Picostat 27
Potentiostat 8
QuadStat 43
Overload indicator
Picostat 28
Potentiostat 8
QuadStat 43

P
pH Amp 2

IndexR

reference electrodeaging and regeneration 94

Ssensorsamperometric 80
biosensors 81
dissolved oxygen 82
microdialysis 82
nitric oxide 83
signal offset
QuadStat 55
signal zero
QuadStat 55
specifications
Picostat 100
Potentiostat 97
QuadStat 102
square wave voltammetry 57
Standby cell111

Potentiostat 18
QuadStat 54
static discharge 25, 39, 41

TTimed Events 65, 78
two-electrode operation
Picostat 27
Potentiostat 15
Potentiostat, electrode connection 7
QuadStat 42

V
voltammetry
cyclic 57, 105differential pulse 57
fast cyclic 59
fast linear sweep 59
linear sweep 57, 105
normal pulse 57
square wave 57

Zzero offset 55
zero resistance ammeter
Potentiostat 16
ZRA mode
Potentiostat 16
Potentiostat, electrode connection 7

112

eDAQ PotentiostatsOverloadPotentiostat

License & Warranty

Trademarks
e-corder and PowerChrom are registeredtrademarks of eDAQ Pty Ltd. All eDAQ software,
hardware, and documentation is protected bycopyright. eDAQ retains the exclusive ownership of
the trademarks and registered trademarks
represented by its company name, logo, andproduct 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 theiractions and the results of their actions.
If problems arise with an eDAQ product, eDAQ will
make 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 inthis Agreement.

Hardware Warranty
eDAQ Pty Ltd warrants the Potentiostat or Picostat, tobe 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 mustfirst notify us before return of the instrument and weeDAQ Potentiostats

will issue you with a RAN (return authorization
number). You must ship the defective product at yourexpense. We will pay return shipping. The productshould be packed safely (preferably in its original
packaging) and have the RAN on the shippinglabel. Returns sent without a RAN may be refuseddelivery.
This warranty does not cover hardware that has:• been modified by the user in any way;
• been subjected to unusual physical, electrical,
or environmental stress. This includes damage
due to faulty power sockets, inadequate
earthing, or power spikes or surges;• been damaged because of incorrect wiring toancillary equipment, or because of substandard,connectors or cables; or• had the original identification marks removed
or altered.

Software License
You have the non-exclusive right to use the suppliedeDAQ software (Chart, Scope etc). Your employees
or students, for example, are entitled to use it,provided they adhere to this agreement. Eachseparate purchase of the eDAQ software licenses it
to be used on two computers at any given time (onone computer for data acquisition with a e-corder
hardware unit, and on a second computer for the
analysis of existing data files). Although multiple

113copies of a program may exist on several
computers, more than two copies must not be usedsimultaneously. Departmental/company licences areavailable if you wish to 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:• the model and serial number of your e-corderunit and Potentiostat or Picostat.
• the type of computer and operating systembeing used (for example Windows XP, or
Macintosh OS 10.2)• the software version you are using (forexample Chart v5.1.2)
We endeavor to answer all your questions, but insome 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 beheard by the Supreme Court of New South Wales inAustralia.

Disclaimer
eDAQ reserves the right to alter specifications ofhardware and software without notice.
No liability can be accepted for consequential
damages resulting from use of eDAQ products.

114

eDAQ Potentiostat