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ii

EChem User’s Guide

This document was, as far as possible, accurate atthe time of printing. Changes may have been madeto the software and hardware it describes sincethen, though: ADInstruments Pty Ltd reserves theright to alter specications as required. Late- breaking information may be supplied separately.

Trademarks of ADInstruments

MacLab and PowerLab are registered trademarksof ADInstruments Pty Ltd. Specic model namesof data recording units, such as MacLab/8e andPowerLab/400, are trademarks of ADInstrumentsPty Ltd.

Chart, EChem, Histogram, Peaks, Scope,DoseResponse, UpdateMaker, and UpdateUser(software), and PowerChrom (software andhardware) are trademarks of ADInstruments Pty

Ltd.Other Trademarks

Apple, the Apple logo, AppleTalk, Geneva,HyperCard, ImageWriter, LaserWriter, Macintosh,and StyleWriter are registered trademarks ofApple Computer, Inc. Finder, MacOS, PowerMacintosh PowerBook, PowerTalk, Quadra,QuickDraw, System 7, and TrueType aretrademarks of Apple Computer, Inc. Windows,Windows 95, Windows 98 and Windows NT aretrademarks of Microsoft Corporation..

PostScript is a registered trademark of AdobeSystems, Incorporated.

BAS is a trademark of Bioanalytical Systems Inc.PAR and EG&G PARC are trademarks of EG&GPrinceton Applied Reasearch. Polarecord is atrademark of Metrohm Ltd. HEKA is a trademarkof HEKA Electronik. PINE is a trademark of PINEInstrument Company. Cypress is a trademark of

Cypress Systems Inc. AMEL is a trademark ofAMEL srl.

I

GOR &I

GOR Pro (software) are trademarks ofWavemetrics Inc.

EChem 1.3 software: Michael Macknight, PeterBromley, Bruce Warrington, and Michael Hamel.

EChem 1.5 software written byLev Possajennikov.

Documentation written by Paul Duckworth.

Document Number: U-MS600-UG-03ACopyright © July 1999ADInstruments Pty LtdUnit 6, 4 Gladstone RoadCastle Hill, NSW 2154AUSTRALIA

e-mail: [email protected]://www.adinstruments.com

All rights reserved. No part of this document may be reproduced by any means without the priorwritten permission of ADInstruments Pty Ltd.


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EChem User’s Guide iii

Contents

Contents

iii

1 Getting Started

1Learning to Use EChem 2Computer Requirements 3The EChem System 4Installation Instructions 6Opening EChem for the rst time 6

2 EChem Basics

9An Overview of EChem 10Opening an EChem File 12Closing or Quitting an EChem File 14The Main Window 14Recording 19

3 Setting Up EChem

23Using 3rd Party Potentiostats 24

Connecting to PowerLab 24Adjusting the Input Range 25Using the Input Amplier Dialog Box 26Units Conversion 29

The ADInstruments Potentiostat 31Changing Potentiostat settings 31The Potentiostat Dialog Box 31

4 Data Display and Analysis

37The Main EChem Window 38

The Axes 40Dragging and Stretching the Axes 42Graph Lines, Patterns & Colors 43

Navigating 44Overlaying Pages 45The Zoom Window 47Display and Printer Resolution 49Making Measurements 50

Using the Marker 50Setting and Removing Baselines 51The Marker Miniwindow 52

Background Subtraction 54The Data Pad 55

Adding Data to the Data Pad 57Setting Up the Columns 57Data Pad Miniwindow 59Printing the Data Pad 59

Computed Functions 59Sampling Speed 60Channel Functions 61Math 62Function 63

The Notebook 64The Page Comment window 65

5 Working With Files

67Selecting Data 68Editing Data 68Transferring Data 69Measuring From the Waveform 71

Using the Marker 72


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iv


Setting and Removing Baselines 73

Saving Options 74Appending Files 77Text Files 77Printing 79

Page Setup 80The Print Command 82

6 Customizing EChem

87Preferences 88

Menus 88Controls 90Options 91Start-Up 92Emergency Access! 92

Macros 94Recording a Macro 95Playing a Macro 96Deleting a Macro 96Macros That Call Other Macros 97Options When Recording Macros 98Macro Commands 101

7 EChem Techniques

107Introduction 108General Considerations 110Linear Sweep Voltammetry 116Square Wave Voltammetry 121Normal Pulse Voltammetry 126Differential Pulse Voltammetry 130Stripping Techniques 135Cyclic Voltammetry 140MultiPulse Voltammetry 146MultiPulse Amperometry 154The Apply Technique... command 159Polarographic Techniques 160

8 Additional Techniques

161Introduction 162AC Voltammetry 163Fast Scan Techniques 163Low Current Experiments 166Chronoamperometry 167

Chronocoulometry 173Chronopotentiometry 175The Potentiostat as a Galvanostat 175Controlled Potential Electrolysis 178Controlled Current Electrolysis 179Rotating Ring Disk Electrodes 180Amperometric Titrimetry 180Liquid Chromatography Detectors 181Biosensors 182Potentiometric sensors 182

pH Electrodes 182Ion Selective Electrodes 183Potentiometric Redox Electrodes 184Dissolved CO

2

and NH

3

Electrodes 184Electrode Behaviour 184Multiple Point Calibration 185pH and ISE Calibration 189Temperature Compensation 194Isopotential Point 196

Potentiometric Titrimetry 197Dissolved Oxygen, dO2, Sensors 198Conductivity Sensors 198Simple Galvanic Cells 199Quartz Crystal Microbalance 200Electrochemical Noise Experiments 200Corrosion Measurements 201

9 Using 3rd Party Equipment

205Introduction 206EG&G PARC 206BAS

210PINE

214Metrohm

215Schlumberger

216Radiometer

216HEKA

217Cypress

218AMEL

220

http://-/?-http://-/?-


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Chapter — Contents v

Appendices

A Menus & Commands

223Menus 223Keyboard Shortcuts 226

B Troubleshooting

227Technical Support 227Solutions to Common Problems 229

C Technique Summary

241Linear Sweep Voltammetry 242Square Wave Voltammetry 243Normal & Reverse PulseVoltammetry 244Differential Pulse Voltammetry 245Cyclic Voltammetry 246Multi Pulse Voltammetry 247

D Electrochemical Equations

249Linear Sweep and Cyclic Voltammetry, TheRandles-Sevcik Equation 249Differential Pulse Techniques, The Parry-Osteryoung Equation 251Chronoamperometry, The CottrellEquation 252Chronocoulometry, The Integrated CottrellEquation 253

E Cyclic Voltammetry, Solvents &Electrolytes

255Solubility Rules 255Solvent Stability 256Use of Large Ions as Electrolytes 256Electrode and Cell Design for OrganicSolvents 259Synthesis of Selected Electrolytes 261

Purication of solvents 264Supercritical Fluids 265The Mercury Electrode 265

F Potentiostat Designs

267Two electrode systems 267Three electrode systems 268Four electrode systems 270

Bibliography

273The Internet 273Text Books 274 Journals 279

Glossary

281

Index

285

Licensing & Warranty Agreement

295


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1

C H A P T E R O N E

1

Getting Started

Welcome to the ADInstruments PowerLab/EChem electrochemistrysystem. EChem software lets you use your computer

*

and PowerLab

analog-to-digital interface unit as an electrochemistry workstationsuitable compatible with a wide variety of potentiostats and patchand voltage clamps. EChem causes the PowerLab unit to generate thpotential waveform for most staircase ramp and pulse voltammetrictechniques, as well as pulsed amperometric experiments, samplesand signal averages the current signal at appropriate times, anddisplays the results in real time. Chapter 7 has a full description of thtechniques available. In addition, when used with the ADInstrumentPotentiostat, full software control of gain ranges, lter settings andpolarity convention is available.

Many other types of electrochemistry experiment can be performedwith the Chart and Scope software included with your PowerLabsystem. Consult Chapter 8 for further details of these experiments.

This chapter contains instructions on the installation of EChemsoftware, and its hardware requirements.

*. EChem software, version 1.5, is suitable for use with Macintosh, Windows 95,98, NT, 2000 or Me computers.


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2


Learning to UseE

Chem

Where to Start

To install and use EChem you should be familiar with the operatingsystem of your computer.

You will nd that EChem works similarly to other programs that youuse on your computer. If you have used earlier versions of EChemsoftware, you should nd that although this version has much incommon, it also has many new features.

Start by reading the introductory chapters in yourGetting Started withPowerLab booklet

which describes how to connect the PowerLab unitto your computer. If you are not using an ADInstruments Potentiostatthen you should also read Chapter 9 before using the system. If youare new to electrochemical techniques, then rst familiarise yourselfwith the various terms dened in the Glossary at the end of thisguide.

How to Use this Guide

If you are in a hurry at least read the rest of this chapter, and theOverview of EChem in the next chapter, to familiarise yourself withsome of the key features of EChem before you begin yourexperiments.

We recommend, however, that you work through this guide in frontof your computer. The information in the following chapters is set ouin the order you will probably require it. If you are unfamiliar withelectrochemical methods then read Chapters 7 and 8. The appendicesalso have much useful information including electrolyte syntheses,solvent purication methods, and sources of general information.

The rest of this chapter, covers system congurations and installingand personalising your copy of EChem.

If you are using a third party potentiostat with EChem then pleaseread the potentiostat operator’s manual carefully to determine itslimitations safe operating procedure. In particular be aware of the


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Chapter 1 — Getting Started 3

maximum potential and current that your potentiostat can generate.Never touch the electrodes while the potentiostat is in operation asthis is extremely dangerous with high powered models.

Computer Requirements

Your particular needs will determine the computing requirementsand hence which model of computer you use. Your ADInstrumentsrepresentative will be happy to discuss your requirements andsuggest suitable congurations.

Apple Macintosh

Minimum

: The minimum requirement is a Macintosh computer witha 68020 microprocessor and a hard disk, System 7, 8MB RAM, and13 inch monitor. If you own an early model Apple Macintosh then wcan supply EChem version 1.3 on request. Although EChem 1.3 hasfewer features than EChem 1.5, it will run even on early model 6800Apple Macintosh computers with System 6 or System 7, and oncomputers with 9 or 12 inch black and white or color monitors (forexample a Mac SE with system 6 will happily run EChem version1.3). Data les collected with EChem 1.3 can also be opened withEChem 1.5.

Chart and Scope software, versions 3.3.8, are also available for usewith PowerLab units used with early model Apple Macintoshcomputers.

Recommended

: a Power Macintosh G3, with a hard disk, System 8,32 MB RAM, and a 14-inch or larger color monitor.

Printers

: there are numerous printers available that can be used toproduce reports from EChem. Some recommended printers are: theApple Color StyleWriter 2500, a color inkjet printer producing high

quality color printouts at near laser printer quality; and the AppleLaserWriter series. If you buy a laser printer ensure that it has truePostScript

®

capability — which will ensure that you get the highestquality graphic output for plotting your results.

Note

Owners of Apple Macintosh PowerBookswill need a suitable SCSIcable or adaptor, available from your computerdealer, to connect thePowerBook to thePowerLab unit. Recent

Macintosh models have aUSB port which can beused as an alternative tothe SCSI connection withPowerLab units with USB ports.

Note

The pictures used asillustrations in this guideare from a monochromemonitor. There may beslight differences inappearance when usingEChem on a greyscale orcolor monitor.


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4


Microsoft Windows

Minimum

: An IBM compatible computer with Pentiummicroprocessor with Windows 95, Windows 98, or Windows NT(v4.0) operating system, and 16 MB RAM (32 MB for NT), and a 14inch or larger monitor, a color VGA card and a CD ROM or oppydisk drive. A suitable SCSI card will need to be installed (contactADInstruments for names of suitable brands).

Recommended

: An IBM compatible computer with Pentium-level orfaster CPU and a fast hard disk, Windows 98 or Windows NT (v4.0)operating system, at least 32 MB RAM (48 for NT), an acceleratedcolor Super VGA card (or equivalent), and a 16-inch or largermonitor, and a CD ROM. A suitable SCSI card will need to beinstalled (contact ADInstruments for names of suitable brands).

Printers

: there are numerous printers available that can be used toproduce reports from EChem, most Windows compatible printerswill be suitable — but dot matrix and other low resolution printersmay not give you the graphic resolution you require for publicationquality diagrams. If you buy a laser printer ensure that it has truePostScript

®

capability — which will ensure that you get the highestquality output when plotting your results.

The EChem System

The EChem/PowerLab system is an integrated hardware andsoftware system designed to record, display, and analyseexperimental data. The PowerLab hardware interface is connected between the potentiostat and the computer. EChem software runs onthe computer to which the PowerLab is connected. You must haveinstalled software on the computer and connected the PowerLab

hardware to the computer to collect experimental data. However, preexisting data les can be opened with, analysed by, and printed fromthe software, whether or not the PowerLab unit is connected.

Data collected with EChem software on a Windows computer can beread by the Macintosh version of EChem and vice versa. You can

Note

Your Windows computerwill need a suitable SCSIcard and cable to connectto the PowerLab unit.Depending an yourcomputer you may needan ISA, PCI or PCMCIASCSI card, available fromADInstruments or yourlocal computer supplier.Old SCSI cards originallyinstalled in Windows 3computers will probablynot work.


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transfer data between computers on Windows formatted oppy disk(Macintosh computers read Windows formatted disks).

Other ADinstruments software that runs with PowerLab units,includes Chart and Scope software (supplied with the PowerLabunit). Other software that can be used with your PowerLab hardware

is available separately and includes PowerChrom software (forchromatographic data collection), and DoseResponse software (forpharmacological studies).

Compatible MacLab or PowerLab Units

EChem 1.5 software can be used with the following new and oldermodels of PowerLab and MacLab.

PowerLab e systems:•PowerLab/200, MacLab/200, MacLab/2e•PowerLab/400, MacLab/400, MacLab/4e, MacLab/4•PowerLab/800, MacLab/8e, MacLab/8

PowerLab S systems:•PowerLab/4

SP

, PowerLab/4s, MacLab/4s•PowerLab/8

SP

, PowerLab/8s, MacLab/8s

•PowerLab/16

SP

, PowerLab/16s, MacLab/16s•PowerLab/4

ST

The PowerLab/410 is unsuitable for use with EChem software.Consult your ADInstruments representative for the latest informatioon our range of products. Please note that MacLab units have now been superseded by the PowerLab range.

Optional Analysis

For general purpose data analysis and the production of specialistplots for theses, reports, slides, and publications we recommend I

GORPro

software (WaveMetrics). Other suitable graphing softwareincludes Origin

(Microcal) and Kaleidagraph

(Synergy).


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6 EChem User’s Guide

Installation InstructionsYou will have been provided with a CD ROM which contains theEChem installer software. If your computer does not have CD ROMcapability then contact your ADInstruments representative who canarrange installation from a set of oppy disks. You will need at least MB of free space on your hard disk for the installation. It isrecommended that you rst install the Chart and Scope software thatalso came with your PowerLab system. To install EChem:

1. Insert the EChem PowerLab CD ROM into the appropriate drive2. Double click the installer icon.The installation creates an EChem folder (directory) in which you wind the EChem program and sample data les. On Macintoshsystems the ‘Potentiostat’ driver software is also placed in the‘ADInstruments’ folder in the System Folder. On a Windows systemthe Potentiostat driver is part of the EChem software. This driver isonly required if you are using the ADInstruments Potentiostat.

If you have used an earlier version of EChem it is stronglyrecommended that you remove these versions from your Macintoshhard disk before you install EChem 1.5. On Windows systems olderversions of software will be automatically uninstalled. Data les fromearlier versions of EChem will open with EChem version 1.5. If ther

are multiple versions of a program present on your hard disk thenyou may accidentally use the older version for your experiments.

Keep your installer CD ROM in a safe place after the installation.Please remember that each purchased copy only licenses you to usethe software on one computer at any one time. Please enquire about acost–saving departmental license if you want to run multiple copiesin your workplace.

Opening EChem for the rst timeEnsure that the PowerLab unit is connected properly to yourcomputer (this is covered in theOwner’s Guide that came with yourPowerLab unit), and that it is turned on. Click the EChem icon andselect Open from the File menu (or double-click the icon). There may be a short delay while the program initialises the PowerLab unit.

Figure 1–1The EChem program icon


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When you start EChem for the rst time, a dialog box will appear(Figure 1–2), asking you to name the copy of the application. If thecomputer has an owner’s name already assigned (for le sharing),then the name will be put into the Name box. Just start typing if youwant to overwrite it.

If the PowerLab unit is not connected, then the dialog box inFigure 1–3 will appear. If this dialog box appears when the PowerLab unit isproperly connected and turned on, see theOwner’s Guide

that came

with your PowerLab for help. Some of the information about start-uproblems from theOwner’s Guide

is also repeated in Appendix B atthe back of this manual.

The PowerLab is not connected or not turnedon. Click on the Analysis button to open a datale for further analysis or for printing.

The SCSI card has not been installedcorrectly or the computer was turned onbefore the PowerLab unit.

The the PowerLab unit is not turned on or notconnected. Click on the Analysis button to opena data le for further analysis or for printing.

Figure 1–3 Dialog boxesthat appear (Macintoshupper, Windows lower) if thePowerLab is not present ornot connected.

Figure 1–2 Enter yourname and that of yourorganization when yourstuse EChem.


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Quitting EChem

If you want to exit EChem after naming your copy of the software,choose Quit from the File menu. If you want to proceed, workingthrough this guide, you can leave the le open.


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EChem User’s Guide 9

C H A P T E R T W O

2EChem Basics

EChem is a sophisticated program for performing voltammetric andamperometric electrochemical experiments. This chapter provides a

general overview of EChem, looks at the main graphic window, anddeals with the basics of recording data.


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An Overview of EChemEChem, together with the PowerLab hardware and computer, givesyou the display capabilities of a two-channel storage oscilloscope, aswell as the features of a versatile waveform generator. You canperform a variety of electrochemical techniques with any potentiostathat has an external input and analog (XY, or chart recorder) outputs.

Display Controls—Chapter 4

Your results are displayed in the main EChem window which can beresized, and the control panels moved to where you want them. Thedata display can be set to show I (current), E (potential) and t (time)in different formats:

• I vs E, with I on the Y and E on the X axis.• E vs I, with E on the Y axis and I on the X axis.• I and E on separate graphs versus time.• I versus time (for amperometric experiments).

The current and potential axes can be dragged, stretched, or set toexact values for optimum data display. The current range can beadjusted. If an ADInstruments Potentiostat is connected then itscontrols can also be accessed through the software. Display colors,patterns, and grids can be altered.

Display and Analysis—Chapter 4

EChem records data in sweeps, like a normal oscilloscope, howevereach new sweep is recorded to a different ‘page’, creating a set ofrecorded scans numbered for easy reference, or for overlaying. Thus new le does not have to be created for each experiment. You can adyour own written comments to each ‘page’ of data to emphasize

features of interest, or to log standard concentrations. There is also aNotebook feature for making general observations about a data le.

When you have nished recording, you can move through your datausing the page controls and make measurements directly from therecording — you are given a direct read-out, with no chance of


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Chapter 2 — EChem Basics 11

measurement errors. You can measure from a selected reference poiusing the Marker, or a baseline (which you can also set). EChemallows you to overlay data from any selection of pages, for directcomparison. The Data Pad feature enables you to make and storeparameters such as peak height, potential at peak height, etc. EChemhas a Zoom window for examining a section of the recording in mor

detail. Refer to Chapter 5 for more details. Working with Files—Chapter 5

EChem results can be printed, edited, and saved to a disk for laterreview. You can also save ‘settings les’ — empty data les that areprecongured for particular experiments — so that any experimentcan be repeated quickly and easily, without having to go through theprocess of entering all the sweep parameters again. Pages of data ca be printed in a variety of formats, or cut, copied, and pasted betweeEChem les, and whole les can be appended to the end of an openle, allowing you to produce summaries in a single le. Data can betransferred as text to spreadsheets or word processors and,conversely, correctly formatted text can even be pasted into anEChem le.

Techniques— Chapters 7 and 8

EChem provides a range of electrochemical methods from simple

staircase linear sweep voltammetry through to complicated pulsesequences. You can dene the sampling periods for each step or pul

Customising and Automating— Chapter 6

EChem can be extensively customised for your purposes. Controls,and menus and their commands (and Command-key/Control-keyequivalents) can be locked, hidden, or altered, and the appearance oEChem simplied, say, for student or technician use. Macros can als be created to automate complex, or repetitive tasks.


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Opening an EChem FileTo open an EChem le,:

1. click on one of the EChem icons in the Finder to select it, and

choose Open from the File menu; or2. double-click the icon (seeFigure 2–1).

There will be a short delay while EChem initialises the PowerLab.The top icon inFigure 2–1 shows the EChem application, which willopen a new untitled le if double-clicked. The second icon shows ale of prerecorded data. The last two icons show a settings le andmacro le — these are like the ‘template’ or ‘stationery’ les used insome spreadsheet or word processor documents. If you open ether of

these then an empty, but precongured, document will be openedready to begin a new experiment.

It is best to have the sample EChem data le open while workingthrough this section, so that you can try the commands, controls, andsettings as they are discussed in the text. First, make sure that thePowerLab unit is properly connected to your computer, and that it isturned on. You may also wish to learn EChem without the PowerLab— if you have taken a copy for your home computer for instance. Inthis case, on opening a le, a dialog box will offer the Analysis optiowhich allows you to use EChem to view and manipulate existing datwithout the PowerLab attached. Unusable controls appear dimmed.

In each case, EChem opens and the EChem window will appear. Bydefault, a new, untitled le will ll the screen. Its size can then bereadjusted if need be.

Once the EChem application has already been loaded, you can openanother le or create a new one by choosing Open… or New from thFile menu. The Open dialog box appears (Figure 2–2). By default onlyEChem les are shown in the scrolling list. You can navigate throughyour hard disk to nd the le you want. EChem allows you to openonly one le at a time.

There are two radio buttons and three checkboxes at the bottom of thOpen directory dialog box. The radio buttons allow you to choose

Figure 2–1EChem desktop icons:double-click one to openEChem


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between opening EChem les, or ASCII text les which may havecome from other electrochemical systems. Only the selected type ofle is displayed in the scrolling list and is able to be opened. Thecheckboxes allow you to append a le to a currently open le, to loathe settings of the new le, and whether to discard macros when thele is opened. Opening text les and appending les are discussed iChapter 5.

The information in an EChem le is made up of data and settings.Data refers to the recorded waveforms, which are normally loadedwhen opening a le. Settings are of two types:

1. Recording settings: those that affect recording, such as the

current ranges, technique settings—scan rate, pulse height etc.;and2. Display settings: those that affect the way the data looks, suchas the window size, display settings, and menu conguration.(Macros are also stored in a settings le.)

When you start EChem by double clicking an existing data le, or asettings le, then both types of settings are loaded. However, ifEChem is already open and you use the Open... dialogue then thereare several possibilities.

If the Load Settings checkbox is on (marked with a tick or cross —depending on the computer and operating system) when opening adata le, then the data and ‘recording settings’ are loaded. Thesesettings will apply to a subsequent experiment. All settings areretained in memory, and used for all subsequent recording, untilchanged by loading new settings. Opening a settings le (which

Radio buttons

Check boxes

Appearance may vary (as shown)

depending your computer andoperating system. Radio buttons arefull when on and empty when off.Check boxes show a tick or cross when on, and are empty when off.

Note

To start EChem with its factory default settings,hold down the Commandkey (Macintosh) orControl key (PC)immediately after youstart the software bydouble-clicking the icon.Release the key when thealert box appears, andclick the OK button.

Figure 2–2The Openle dialog box


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contains no data) with the Load Settings checkbox off will load onlydisplay settings, not those affecting recording of data.

If you have a le open when opening a second le, then the rst lewill be closed. If there are any unsaved changes to the rst le, analert box will appear asking if you want to save them before opening

the new le. If the Load Settings checkbox is on, then both thesettings and the data will be loaded, otherwise the current settingsfrom the rst le are retained.

Using the sample data le as you work through this user’s guide willshow you some real data and perhaps give a better idea of what isgoing on in EChem.

Closing or Quitting an EChem File

To close an EChem le, choose Close from the File menu or click inthe close box in the Main window (upper left corner,Figure 2–3). Toquit EChem, choose Quit from the File menu. In either case, if youhave made any changes, a dialog box will appear, asking you if youwish to save your work. Click the Save button if you wish to keep thchanges you have made. Click the Don’t Save button if you want todiscard the changes.

The Main Window The essential controls for recording data are provided in the Mainwindow and its various control panels, illustrated inFigure 2–3.These controls are discussed below, and in greater detail elsewhere inthis manual. The window itself consists of, the data display area,which contains recorded data; and some controls at the bottom of thewindow. Various movable control panels surround the windowproper. The menu bar at the top of the screen contains the EChemmenus (see Appendix A), allowing you to set up and modify the way

EChem looks and behaves. The EChem Window command from theWindows menu returns to this window from another, or opens a new,untitled le if the window has been closed.


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Basic Window Controls

The close box, title bar, zoom box, and size box all work as they do other software.

Click the close box to close an open EChem le (this is the same aschoosing Close from the File menu). The title bar shows the title ofthe le, and has horizontal lines across it if it is active (that is, thefrontmost window). Drag the title bar to move the EChem window tanother area of the screen, or to another monitor if you have oneattached (you can do this while recording). Drag the size box to setthe size of the window: this is useful if you want other applicationson the screen, and does not affect recording delity — the resolutionof recorded data is independent of the resolution of the display. Clic

Close box

Title bar File title Zoom box

Scalepop-upmenu

The data display area is empty

when opening a new le

Axis label

Display pop-up menu(i vs E display selected)

Page buttons

Marker

Size box

Page Commentbutton

Cursor informationpanel

Rangepop-upmenu

Input Amplierdialogbutton

Start/Stopbutton

i Channelcontrolpanel

Techniquedescription

Scalepop-upmenu

Page Cornercontrols

‘Vertical space’

Figure 2–3The Main window of a newlycreated le showing the i vs Edisplay mode


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the zoom box to toggle the EChem window between a set size and thfull size of the screen.

The three control panels (Cursor, i Channel, and Sample) cannot beresized, but they can be moved independently around the screen ifnecessary. Blank panels appear behind the control panels to reduce

clutter: these, too, can be moved.Navigating

EChem stores sweeps of data as if they were pages in a pad of paper.The numbered Page buttons along the bottom of the EChem windowand the Page Corner controls (the ‘dog-ears’) at the bottom right ofthe data display area allow you to move through multiple pages of anEChem le. The highlighted Page button indicates the page of datacurrently viewed. EChem will always have one blank page, the lastone, in a le. As pages of data are recorded, they are numberedconsecutively, with the blank page remaining at the right. New data irecorded to this page.

Click the upper, folded corner of the Page Corner controls to move tothe next, and the lower corner to move back to the previous page.Clicking the numbered Page buttons takes you immediately to thatpage, or choose Go To Page… from the Display menu, or typeCommand-G (or Control-G), and enter the number in the dialog boxthat appears. If there are too many pages to show all the buttonsalong the bottom of the window, then left and right arrow scrolling buttons will appear at either side: click them to move a page left orright, or press them to scroll left or right through many pages.

You can also move a page left or right by pressing, respectively, theleft and right arrow keys on the keyboard. Hold down the Command(or Control) key while pressing the left or right arrow key to go to th beginning or the end of the le (the rst or last numbered pages).

The EChem AxesWhen EChem is displaying both I and E versus time, or I versus timethere will be a horizontal Time axis, above the Page buttons along the bottom of the Main window. This shows the time from the start ofsampling, When the I versus E display mode is chosen, the horizonta

Scrolling buttons

Blankpage

Activepage

Page Corner controls


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axis becomes the applied potential (E) and the vertical axis therecorded cell current (I). This is reversed for the E versus I mode.

Note that the graph area remains blank until some data is actuallyrecorded. The scale for each axis is initially set by the current rangecontrol on the right side of the window and the chosen technique.Both i and E axes can be stretched or dragged using the pointer.Display options can be chosen from the Scale pop-up menu.

The i Channel (current) Control

The current scale settings are located at the right of the main windowThe control panel is labelled ‘i Channel’,Figure 2–4.

The i Channel panel, controls the current sensitivity and setup of

either the PowerLab Channel 1 input amplier, or the ADInstrumentPotentiostat, if connected.

If you are using the ADInstruments Potentiostat press the Range popup menu to choose the full scale current range (±20 nA to±100 mA).Click on the Potentiostat button to bring up a dialog that allows youto adjust the Potentiostat settings — lters, polarity, dummy/real celsetting, etc.

If you are using another brand of potentiostat then click the Input

Amplier button to bring up a dialog box to adjust the Channel 1controls of the PowerLab. The signal for the potentiostat is a voltagelevel that represents the current signal. You will have to adjust theinput sensitivity to your potentiostat full scale output (often 1 or 10 — read the potentiostat manual). For example if you are using a BACV-27 potentiostat, which you have adjusted to a setting of (say) 1µA/V, you will still need to keep the PowerLab i Channel setting at10 V because this is the maximum output from the plotterconnections of the CV-27, that is, the CV-27 can report currents of uto 10µA when set at 1µA/V.

Technique Description Panel

The area under the i Channel settings displays information about tothe selected sweep including the its name, start and end potential,sweep rate, etc. Once the scan has been completed the time and dateare also displayed.

Figure 2–4The i Channel control panel:for 3rd party potentiostats,and (lower) for theADInstruments Potentiostat


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Data Display Area

Data is displayed in the Main Window in the area bounded by the iand E axes, or the i, E and time axes when in the iE vs t mode. Whenthe iE vs time display mode is chosen, two channels are displayed.The channel separator between them can be dragged by the blackhandle at its right end up or down to vary the size of the channeldisplay areas. Dragging it to the top of the display or double-clickingit will overlay channels A and B in the one display, Chapter 4.

Cursor Panel

The Cursor panel shows the value of the coordinates of the cursorposition as the pointer is moved over the data display area. Forvoltammetric experiments it displays the current (I), potential (E),and time (t) values which are updated constantly as you move thecursor along the waveform. For amperometric experiments viewed inthe I vs t mode only time and current are reported. The Cursordisplay will be blank if the pointer is not over the waveform displayarea. If the Marker (see below) is positioned on the trace then thedifferences,∆ , in current, potential, and time between the marker andcursor positions are also displayed.

The Marker

The Marker can be found in the box at the bottom left of the EChemwindow. It can be dragged onto the data display area to a particulardata point on the voltammogram which becomes the ‘zero’ referencepoint. Relative measurements can now be made. Double-clicking theMarker or clicking its box sends it back home. You can also drag themarker close to its lair and let go of the mouse button. The markerwill automatically nd its way back.

Page Comment Button

The Page Comment button can be found at the bottom left of theEChem window, to the right of the Marker. Click it to bring up thePage Comment window for noting down comments about particularpages of data, for example you might want to enter theconcentrations of metal ions in a standard solution. When there are

The ‘page comments’button changesappearance when acomment is added

The ‘marker’ can bedragged onto the trace


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comments noted down for the active page, the button icon changesfrom a blank note to a marked one.

Start Button

To start recording, click the Start button in the Sample panel. The button then changes to Stop — click it, if required, to stop recordingThe button may show a dimmed Wait… while starting or stopping.After the rst sweep in a new le you will be asked to save the le.Second and subsequent sweeps will be automatically saved at the enof each sweep. This autosave feature can be turned off from thePreferences/Options command in the Edit menu.

Pointer

The pointer will change shape as you move it about the EChemwindow, giving you an indication of its function in certain areas — i becomes an I-beam over a text entry area, and a cross in the grapharea, for instance. It becomes dimmed when it cannot effect a functiunder particular conditions. Do not confuse the ‘pointer’ (controlled by the mouse) with the ‘cursor’ that follows the pointer when it is inthe data display area, but which remains on the trace. It is thecoordinates of the cursor that are reported in the Cursor Panel, and ithe Data Pad.

RecordingTo start recording (sampling), click the Start button in the Samplepanel in the lower right hand corner of the screen. The button thenchanges to Stop — click it, if required, to stop recording. The buttonmay show a dimmed Wait… while starting or stopping.

EChem emulates some of the basic functions of a standardoscilloscope, proving a visual image of an electrical signal against

time. However, unlike oscilloscopes EChem lets you record a largenumber of sweeps as different ‘pages’ of data, creating a series ofrecorded waveforms, automatically stored and numbered for easyreference. EChem can overlay any selection of these stored sweeps.Also a single background sweep can be subtracted from sweeps thatwere recorded under similar conditions (same scan rate, start andnish potentials etc.).

The pointer can be a cross,I-beam, or arrow shape

Note

EChem does not record inthe background: it must bethe active (top) applicationto function.


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Display While Recording

At slow sampling speeds you will see data drawn on the screen as itis recorded. A short vertical line segment, the Trace Indicator, movesleft to right across the top of the data display area, tracking the frontedge of the advancing waveform as it is drawn on screen.

At fast scan rates, it will appear that the whole scan of data is drawnat once, and no Trace Indicator is seen.

Interruptions While Recording

You can stop sampling mid way through a scan, by clicking the Stop button in the Sampling panel, or typing Command-period (Control-period) or Command-spacebar (Control-spacebar). EChem will stopthe scan but retain the data already recorded (as long as the ‘KeepPartial Data’ box is checked in the Preferences/Options... commandof the Edit menu).

Please note that EChem does not record in the background. It must bthe active, or top, application while recording. If you switch toanother application (including the Finder) by choosing it from theApplication menu or clicking outside the area of the EChem windowand its control panels, then EChem will stop recording. On switching back to EChem, the experiment will restart.

Length of Recording

The number of pages of data that you can record depends primarilyon the memory that you have allocated to EChem. If you nd thatyou run out of memory, you can increase EChem’s memory allocatioon Macintosh by quitting, selecting the application icon in the Finderchoosing Get Info from the File menu (or typing Command-I, orControl-I), and typing a larger value in the ‘Preferred size’ box. Ther

is an upper limit of 1000 pages in any one le.The amount of memory available for recording on Macintosh can beseen in the lower portion of the EChem dialog box,Figure 2–5 , byselecting the About EChem… command from the Apple () menu(click the dialog box to make it go away again).


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On a Windows PC the amount of memory is allocated by theoperating system and you can record data until you run out of harddisk space (or exceed 1000 pages).

Data is compressed while it is being recorded, the efciency ofcompression depending on how the signal varies: signals that changvery slowly, such as a straight line or gradual curve, can becompressed a great deal, while complex and rapidly changing signalmay not compress much at all. The extent of compression is usuallyin the order of 25–33%.

On a Macintosh EChem uses a certain amount of memory for an offscreen buffer to speed up data display. If the EChem window is largand the display is grayscale or color, more memory is used, especialif the monitor display has been set to thousands (16 bit color) ormillions (24 bit color) of colors. If the EChem window lled a 14"monitor displaying millions of colors, the memory used by thiswould be about 1.25 MB. If you nd yourself running out of memoryou can use less by shrinking the EChem window to a smaller sizeand changing the display to 256 colors (or even grayscale or blackand white). Since EChem only uses eight colors there is no advantagto be gained by running in thousands or millions of colors.

The largest EChem data le, 1000 pages at about 10 K per page, coutake, at worst, up to 10 megabytes of memory (but probably more li7–8 Mb), plus the overhead necessary for EChem to maintain the ofscreen buffer. Of course it is much more likely that your experimentwill only have a relatively few pages of data and that it will occupymuch less space (usually much less than a megabyte).

Figure 2–5The available memoryindicator bar on a Macintosh.


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C H A P T E R T H R E E

3Setting Up EChem

EChem software supports the use of many third party potentiostatsas well as the ADInstruments Potentiostat.

This chapter describes connection of third party potentiostats to thePowerLab, and basic settings controls such as the current range andunits conversion. Also described is the use of the ADInstruments’Potentiostat with EChem software.

For more information about third party potentiostats see Chapter 12


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Using 3rd Party PotentiostatsEChem can be used with numerous third party potentiostats. If youare using an ADInstruments’ Potentiostat you can skip this sectionand start reading from ‘The ADInstruments Potentiostat’.

If you own an existing potentiostat then there is a good chance that itwill be able to be used with an EChem system. Chapter 12 lists a widvariety of compatible third party equipment. You should refer to thischapter to determine if your potentiostat is compatible with EChem.More information can be obtained by e–mailing us [email protected]. Please contact your ADInstrumentsrepresentative if you wish to make specic enquiries regardingcompatibility with your equipment.

Connecting to PowerLabMany commercial potentiostats are suitable for connection to aPowerLab unit and can be operated with the EChem software. Theseinstruments must have the ability to accept an external waveform.You may need to consult Chapter 12 or your potentiostat’s usermanual to see if an external input is available.

You will need to connect the analog output of the PowerLab to the

external input of the potentiostat. This will usually be located on thepotentiostat front or back panel and will be labelled ‘E in’, ‘ExternalInput’, ‘Ext. In.’, or something similar. Connect the potentiostatexternal input to the PowerLab ‘Output +’ (or ‘Output 1’) BNC frontpanel connector.

Different manufacturers use opposite conventions about whether anegative potential corresponds to reduction or oxidation at theworking electrode. If you nd that after connecting to the PowerLabthat your peak potentials are the opposite polarity to that which you

expect (for example a peak is found at +0.25 V when it should be at–0.25 V) then remove the cable from the PowerLab ‘Output +’ (or‘Output 1’) connector and attach it to the PowerLab ‘Output –’ (or‘Output 2’) connector. This reverses the polarity of the potentialwaveform signal, which in turn will change a reducing potential to anoxidising potential (and vice versa) at the working electrode.

CAUTION

Many potentiostats arecapable of producingdangerous, even possiblylethal, current/voltagecombinations. You shouldnot attempt to use a potentiostat before readingits manual and thoroughlyacquainting yourself withany possible hazards thatmay be associated with itsuse.


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Chapter 3 — Setting Up EChem 25

In order to record current and potential data you will need to locatethe potential and current outputs located on your third partypotentiostat. These are often labelled as ‘Applied E’, ‘App. E’, ‘E ou‘E monitor’, ‘I monitor’, ‘I out’, or something similar. The current (I)output of the potentiostat should be connected to the CH1+ connectoof the PowerLab. If you need to sample the potential values, then th

potential (E) output of the potentiostat should be connected to theCH2+ connector of the PowerLab. Potential monitoring can be donein EChem in the Multi Pulse method if potential sampling is selecte

For most methods in EChem the potential values that are used forplotting are the calculated potentials — it is assumed that thepotentiostat will accurately follow these. Thus the points are alwaysexactly evenly spaced along the potential axis. Note, however, thateven if you do not connect the potentiostat to channel 2, EChem stiluses this channel to store the potential values, and thus channel 2

cannot be used for connecting to other instruments.It is possible to alter the cable that links your potentiostat to the backof the PowerLab /200 or /400 via the Multiport. Consult thePowerLab Owner’s Guide for the functions of the different pins. However, youshould exercise care when modifying such a cable to ensure thatshorts do not occur between channels, or between signal lines andpower rails. Construction of such a cable should only be attempted ba competent technician. If you have a special requirement then pleascontact your ADInstruments representative.

Adjusting the Input Range

When a third party potentiostat is used with EChem you will have toadjust the range of the ‘i Channel’ (channel 1 of the PowerLab) tomatch the output of your potentiostat. Many potentiostats have a fulscale output of 1 V or 10 V representing current ranges of 1 µA, 10 µA,100 µA, 1 mA, 10 mA, 100 mA, and 1 A.

As an example, if the potentiostat produces an I(out) output of 1 Vrepresenting the full scale setting for the 1 mA current range, then thi Channel range should be set to 1 V. If the output from thepotentiostat was±10 V representing the full scale current range of1 mA then the i Channel range should be set to 10 V (Figure 3–1).

CAUTION

Do not connect a third party potentiostat tochannels 1 and 2 at the front of a PowerLab unitwhile an ADinstrumentsPotentiostat is connected.The results obtained willbe very unpredictable.Similarly if a third party potentiostat is connectedto a PowerLab unit via therear Multiport connectorthen the channel 1 and 2connectors at the front ofthe PowerLab should notbe connected to any otherinstrument.

Please note that the MacLab/2e and /4e unitshave been superseded bythe PowerLab /200 and

/400 models


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If you are dealing with very low currents (which do not give full scaloutput on the potentiostat, even at its most sensitive settings) you cantry choosing a smaller range from the i Channel range pop-up menu.This causes the PowerLab unit to amplify the incoming signal andmay give you a better result — but bear in mind that any incomingnoise will also be magnied.

You can also adjust the i Channel range inside the Input Amplierdialog box. This is discussed in the next section.

Using the Input Amplier Dialog Box

The Input Amplier dialog box (Figure 3–2) allows, among otherthings, software control of the current recording channel in thePowerLab. For EChem this is channel 1 of the PowerLab. The signalpresent at that channel’s input is displayed so that you canimmediately see the effects of any changes. This allows you tomeasure the current signal from the potentiostat and use it to check o

calibrate this channel to appropriate current units. Once you havechanged the settings in the dialog box, click the OK button if youwish to apply the changes to the channel. The Input Amplier dialog box appears when you click the Input Amplier… button in the iChannel panel. The dialog box in Figure 3–2 will appear.

Signal Display

The input current signal is displayed so that you can see the effect ofchanging the settings. Data is not actually being recorded while youdo this — as it disappears from the screen it is lost. The incomingsignal value is displayed at the top left of the display area. Slowlychanging signals will be represented quite accurately, whereas veryquickly changing signals will be displayed as a solid dark areashowing only the envelope (shape) of the signal formed by theminimum and maximum recorded values.

Use this pop-up menu to setthe range of the i channel tomatch the output range of thepotentiostat

Figure 3–1Adjusting the i Channel rangeto match the output range ofthe potentiostat


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Range pop-up menu

Signal amplitude

Pause/Scroll button

Current Amplitude axis

Low passlter

PowerLab/4SP, /8SP and /16SP Input Amplier Dialog. PowerLab/4SP, also features Positive andNegative boxes (not shown here).

PowerLab /200 and /400 Input Amplier Dialog. PowerLab /800 does not have the Positive anNegative boxes.

Figure 3–2The Input Amplier dialog box.

PowerLab /4SP , /8SP and /16SP modelshave a choice of low pass lters from 1 Hzto 20 kHz

Filter:


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If your potentiostat has positive feedback resistance compensation (icompensation), you can use this window to monitor the signal whileyou adjust the amount of compensation. After setting the gain simplyincrease the resistance compensation until the current signal is drivento oscillation, then decrease the amount of compensation slightly(usually by about 10%) so that potential control is re-established.

You can stop the signal scrolling by clicking the Pause button at thetop right of the data display area (it looks like the pause button on atape player). It then changes to the Scroll button (like the play buttonon a tape player): click it to start scrolling again. The incoming signais shown

You can shift and stretch the vertical Current Amplitude axis to makethe best use of the available display area — drag a tick label on theaxis to stretch or shrink, or drag the area between the labels to offset

the axis. Apart from being at the right rather than the left, it is thesame as the Amplitude axis in the main window, and the controlsfunction identically. The Scale pop-up menu to the right of the axis isalso the same. Changes made in the Amplitude axis here will bereected in the main window.

Setting the Range

The Range pop-up menu lets you select the full scale input range, orsensitivity, of the i channel (normally channel 1). Changing the rangein the Input Amplier dialog box is equivalent to changing it in themain window. All dialog box changes are made in the main windowon clicking the OK button.

The range menu will always display full scale volts or millivolts,irrespective of the application of units conversion. The range menustarts at +10 V full scale and can be set as low as 2 mV full scale.

Filtering

PowerLab /200, /400, /800 units can apply a 50 Hz, 2-pole Bessel,low pass lter to the incoming signal which may aid in the removal ohigh frequency noise. With other PowerLab models such as the /4SP ,/8s, and /16s, you can select an appropriate low pass lter (1 Hz to20 kHz) from a menu,Figure 3–2. Your Potentiostat may also havelter settings which can also be used. However, remember that for

The scroll buttonchanges when

clicked on and off


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high speed scans, or for work with short period pulses, you will neeto keep ltering to a minimum.

Differential or Single-ended Inputs?

Most potentiostats provide a single ended output and the currentsignal needs to be connected to the CH1+ of the PowerLab unit. Ifyour potentiostat is giving an exceptionally noisy signal you may alwant to try connecting it differentially as this can sometimes reducenoise levels. The PowerLab /200, /400, /4s, /4SP , /4ST , and olderMacLab/2e and /4e units, can accept a differential signal. Use eitherthe front panel BNC connectors labelled CH1+ and CH1–, or via thefront panel DIN connectors — see the PowerLabOwners Guide. Youwill also need to make sure that you crossboth the Positive andNegative checkboxes to activate the differential input.

Inverting the Signal

The Invert checkbox allows you to invert the current signal from thepotentiostat. It provides a simple way to change the direction of therecorded current signal without having to reconnect leads. Use this iyou nd that your peaks are going to negative current values whenyou would prefer them to go to positive current values (or vice versa

Units

Clicking the Units… button brings up the Units Conversion dialog box, allowing you to display the signal from the potentiostat in thecorrect units of current. This provides an easy way to calibrate thechannel to the range of the potentiostat. Using Units Conversion isdiscussed in the next section.

Units Conversion

To bring up the Units Conversion dialog box (Figure 3–3) click theUnits… button in the Input Amplier dialog box.

Units conversion lets you scale the i Channel Axis so that theincoming current signal from the potentiostat (which is actually avoltage signal) is displayed in appropriate current units such as mAor µA.


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Converting Units

Before using the Units Conversion feature you must turn it on byclicking the On button. Underneath there are two edit text boxes: theleft-hand box is used to enter the potential value, and the right-hand box is used to enter the equivalent current value. Both of the boxesmust have values in order to calculate the relationship betweenpotential and current. You can press Tab to move between the elds.

If, for instance, you are using a potentiostat that produces a 10 Vsignal for a full scale current of 1 mA then you would type in ‘10’ inthe left box and ‘1’ in the right box. Then choose ‘mA’ from theCurrent units pop-up menu. Once you click the OK button the iChannel axis will now display the correct units of current.

You can turn units conversion off or on without losing the values youhave entered by clicking the Off or On buttons.

Applied Potential

The applied potential slider control allows you to adjust the controlvoltage sent to the external input of the potentiostat. To change the

value simply drag the control left or right to set an appropriatepotential — or click on the A-button to enter an exact value.

Current unitspop-up menu

Voltage value, useunits of mV or V Equivalent current valueFigure 3–3 The Units

Conversion Dialog box.

Note

There must be a proportional relationshipbetween the recordedvoltage and the new units for the units conversion towork properly. Most potentiostats provide sucha signal.


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The ADInstruments PotentiostatIf you are using an ADInstruments Potentiostat the EChem interfacewill be slightly different as the Potentiostat is designed to becompletely controlled from within EChem. First connect the

Potentiostat to the PowerLab unit—you should read Chapter 9 fordetails.

Changing Potentiostat settings

When the Potentiostat is properly connected to the PowerLab andyou run EChem you should see the i Channel control panel shown inFigure 3–4.

You should see the Potentiostat button at the bottom of the panel. Ifthe button says ‘Input Amplier’ then quit, turn off the PowerLabunit, recheck the Potentiostat’s connections, and try again. If you areusing a PowerLab/200 or /400 with Multiport connection to thePotentiostat ensure that there is nothing connected to the CH1 andCH2 front panel input connectors of the PowerLab unit.

Adjusting the Current Range

The Potentiostat range control reads directly in full scale currentvalues. The Potentiostat supports ranges from±100 mA down to±20nA. To adjust the current range choose an appropriate full scalecurrent from the range pop-up menu in the i Channel control panel.

The Potentiostat Dialog Box

The additional controls of the ADInstruments Potentiostat can beaccessed by clicking the Potentiostat button in the i Channel controlpanel.

Current range pop-up menu

Click this button to access thePotentiostat dialog box

Thecurrentrange pop-up menu

Figure 3–4 The i Channelcontrol panel.


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This dialog (Figure 3–5) allows you to adjust the current range,ltering and cell connection settings. Galvanostat functions are onlyenabled when using Chart or Scope software, see Chapter 8.

Signal Display

The current signal from the connected cell is shown in the scrollingdisplay area. By using the Dummy or Real modes the effect of anapplied potential can be seen prior to actually recording the data. Nodata is actually recorded when the Potentiostat dialog box is open.When the dialog is closed the signal trace is lost.

You can stop the signal scrolling by clicking the Pause button at thetop right of the display area (it looks like the pause button on a tapeplayer). It then changes to the Scroll button (like the play button on atape player): click it to start scrolling again.

You can shift or stretch the vertical Amplitude axis to make the bestuse of the available display area. Apart from being at the right rather

Signal amplitude

Range pop-up menu

Filter pop-up menu

Cellconnectionmodes

Applied potentialslider control

Pause Button

Applied potentialslider control

Figure 3–5The Potentiostat InputAmplier dialog box


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than the left, it is the same as the amplitude axis in the main EChemwindow.

Setting the Range

The range pop-up menu lets you select the input current range orsensitivity of the Potentiostat. Changing the range here also changesthe range in the Scope and Chart window. The default setting is100 mA and goes to 20 nA in 1, 2, 5 steps.

Filtering

The Potentiostat has a number of low pass lter settings, for removaof high frequency noise at 10 kHz, 1 kHz, 100 Hz, 50 Hz, and 10 HzThe pop-up menu can be used to select the appropriate lter. The 10Hz setting is very effective in removing 50 or 60 Hz mains hum but careful that it does not distort your voltammograms. As a roughapproximation the 10 Hz lter can be used safely for linear sweep ocyclic voltammograms up to about 100 mV/s, or for pulse techniquewhere the pulses are longer than about 100 ms.

For very high speed scans or for work with millisecond pulses youwill need to use the 10 kHz lter setting.

Inverting the Current Signal

The Invert checkbox allows you to invert the signal on the screen. Itprovides a simple way to change the direction of the recorded currensignal. This will allow you to display your data according to whetheyou prefer that a current signal greater than zero represents anoxidation or a reduction process at the working electrode. If you ndthat your voltammetry experiments have peaks that point to greaternegative currents when they should point to greater positive currents(or vice versa) use the invert checkbox.

Cell Control

Three modes are provided to control the way in which thePotentiostat connects to the cell. Each of these modes is analogous tthe settings found on traditional potentiostats.

The lter

pop-upmenu


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Standby – the external cell is disconnected and the internal dummycell is connected to the Potentiostat. When the Potentiostat dialog isclosed and the Chart, Scope or EChem start button is clicked theexternal cell will be connected to enable the experiment. This mode iused if you do not wish to connect to the external cell until theexperiment is actually performed. The Applied Potential control is

disabled in this mode.Dummy – the Potentiostat is connected to the internal dummy cell(an internal 100 k Ω resistor network). You can use the AppliedPotential slider control to vary the voltage applied to the dummy cellThe Potentiostat will remain connected to the dummy cell even whenthe Potentiostat dialog is closed and Chart, Scope or EChem isrecording. This is useful for testing a method using the dummy cell.

Real – the external cell is connected to the Potentiostat while you are

in the Potentiostat dialog. The Applied Potential slider control can beused to adjust the voltage applied to the external cell. When you closthe Potentiostat dialog the external cell will be disconnected until theStart button is pressed and Chart, Scope or EChem begins to recordan new experiment. This is similar to the Standby mode except itallows you to modify the applied potential before the method isstarted.

Applied Potential

The applied potential slider control is enabled in eitherDummy or Real modes. It allows you to adjust the voltageapplied to either the dummy cell or external celldepending on the mode selected. To change the value

simply drag the control left or right to set an appropriate potential —or click on the A-button to enter an exact value.

Reverse Polarity

Depending on your local convention you may wish to dene a ‘moreoxidizing potential’ at the working electrode as either a morepositive, or as a more negative potential.

If the Reverse Polarity box is crossed then the Potentiostat willproduce oxidizing potentials at the working electrode at more


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C H A P T E R F O U R

4Data Display and

Analysis

EChem allows you great exibility in displaying data. You can chanthe lines, patterns, and colors of the display. You can resize the

EChem window, change the size of the channel’s display, or overlaythe voltage and current channel, or invert or interchange the currentand potential axes. You can zoom to see a small section of data ingreat detail, or overlay data from any selection of pages in a le.

The whole purpose of recording data, of course, is to nd things outthrough analysis of the recording. Voltammograms can be measuredusing the Cursor, to give absolute coordinates or relative readingsfrom marker. A background page can be set, so that thevoltammogram on it is subtracted from all others in the le. Theinbuilt Data Pad calculates and stores statistics about recorded data,calculates peak maxima, and areas. The current signal can also besmoothed, integrated or differentiated according to yourrequirements.

This chapter describes the display options available in EChem, fromthe basic settings through to Amplitude axis manipulation and theZoom window, and also discusses the available analysis options.


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The Main EChem Window Recorded data is displayed in EChem’s main window. By default, thecurrent and potential data is displayed in an XY plot with current onthe vertical axis and potential on the horizontal axis (I vs E). You can

also change the display mode to show both potential and currentagainst time (IE vs t), potential versus current (E vs I), or currentversus time (I vs t),Figure 4–1. To change the display choose theappropriate mode from the display mode pop-up menu at the bottomleft of the Main window.

I vs E mode, current on the Y axisand potential on the X axis.

E vs I mode, current on the X axisand potential on the Y axis.

IE vs t mode, current and potential onseparate Y axes and time on the X axis.

I vs t mode, time on the X axis andcurrent on the Y axis.

Figure 4–1There are four main display

modes that can be accessedby the display mode pop-upmenu.

Thedisplay

mode pop-up menu


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Chapter 4 — Data Display and Analysis 39

IE vs t Display — Extra Features

When the display is in the IE vs t mode you can vary the relative sizof the channel display areasFigure 4–2.

By dragging the channel separator to the top of the window you canoverlay the current and voltage signals — the current axis is on theleft, and the potential axis is on the right,Figure 4–2. Both Y axes can be shifted and stretched independently to adjust the graphs asrequired. The channel separator handle moves to the top right of thewindow — double-click it to toggle back to separate channel display

Drag the channel separator (the short black bar)up and down, to the desired position — middlepicture; or double click the separator to overlaythe channels — bottom picture.

Move the pointer over the channel separator. Itchanges shape:

After you have resized the two channels you candouble click the separator to return to equalspacing.

By dragging the separator to the top of the window you can overlay the current andpotential traces.

Position of channel separator in overlay mode.Double click to show separate channels.

Figure 4–2 Changingrelative heights of thechannels and overlayingcurrent and potential data inthe IE vs t display mode.


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The AxesThe limits and direction of the current and potential axes can be setfrom the Scale pop-up menu. The button for which,Figure 4–3 , islocated on the left-hand side of the current axis (when it is the Y axis

or the lower right hand side of the current axis (when it is the X axis,in E vs I display mode). There is a similar button on the potential axiThe Bipolar and Single Sided options are disabled if Units Conversiois already applied.

The current axispop-up menuThe set scale dialog allows you to

enter exact limits for the axis.

Units Conversion (current axisonly) allows you to rescale theoutput of the potentiostat soit displays the correct units. Computed Functions allow

you to transform the data

Location ofthe axismenubutton

Figure 4–3Using the current axiscontrols. Similar controls arefound on the potential axis.


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Single Sided . Shifts the axis so that zero is located at the bottom (orleft) of the display area. This option can be used if you wish to viewonly current signals larger than zero. Any readings below zero will boff the screen (to see them, select the Bipolar option). If the axis is i bipolar display (below) double clicking it will make it single sideddisplay.

Bipolar . This is the default mode for each channel. It displays zero athe centre of the axis. Double clicking the axis will make it return to bipolar display.

Set Scale . This option allows you to adjust the axis directly to displathe range of values you desire. It works whether Units Conversion ion or off. When you choose Set Scale…, the Scale Range dialog boxappears (Figure 4–3), allowing you to type in directly the lower andupper limits of the axis to be displayed.

Note that Set Scale is meant for ne-tuning the scale setting ratherthan for use as a gross magnication tool, and will allow expansion compression to no more than twice the original range chosen, withneither the upper or lower value being over three times the originallimit. First set the range approximately from the Range pop-up menufor the channel, and then set the axis to the precise values required. you are trying to enlarge very small features you should considerusing the Zoom window, or (preferably) recording the data at ahigher gain.

Invert Axis . This will reverse the direction of the axis. Useful if youwant positive current values to go in the downwards direction (ortowards the left when current is on the X axis). The direction of thepotential axis can also be reversed so that oxidative potentials can bdisplayed to the left or right.

Units Conversion … Choosing the Units Conversion item brings upthe Units Conversion dialog box (current axis only) which allows yoto readjust the conversion factors for the current signal. You have achoice of reassigning conversion factors for all the pages in the le just for a particular page. See Chapter 3 for more details of UnitsConversion.

Computed Functions … Choosing this item is the same as selectingComputed Functions... from the Display menu, and is discussed mo


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fully later in this Chapter. You can smooth, and perform variousmathematical transformation on the current signal. You can offset thepotential signal (if you want to set a new reference potential).

Dragging and Stretching the AxesThe scale of the potential and current axes can be independentlydragged (offset) or stretched for optimum data display. This allowsyou to enlarge the signal viewed on the screen, for instance, or moveit to better t in the display area.

The pointer changes as it is moved over the axis area as shown inFigure 4–4. In the data display area, it is a normal, leftward-pointingarrow. Over the axes, though, the pointer leans to the right, and asmall marker appears beside it. Between the axis tick labels, a double

headed arrow indicates that dragging will move the axis. If thepointer is near an axis tick labels then dragging will stretch orcompress the axis.

Dragging or compressing the scale allows you to set the axis to threetimes the range limit, and stretching allows you to expand the axis upto 20 times.

Double-clicking in the axis area returns the scale to its normal,unstretched position, with zero at the mid-point of the axis. Double-clicking again toggles between this Bipolar display and the SingleSided display, which has zero at the bottom of the display area.

Backgroundbuttons

Line typebuttons

Colour pop-upmenu

Graticulebuttons

Figure 4–4 The pointerchanges shape as it movesover different parts of theaxes.

Normal pointer

Pointer as it appearsbetween tick labels —move axis

Pointer whenover tick labels — stretch axis

Figure 4–5The Display Settings dialogbox for changing line typesand colors.


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Graph Lines, Patterns & ColorsThe Graph Lines, Patterns & Colors dialog box allows you to set thetype, pattern, and color of the voltammogram for each channel, thepattern and color of the graticule (the display grid), and whether the

background is white or black. The exibility over the display willdepend on which display mode you are using, IE vs t or I vs E. Thedifferences in the dialog controls is shown inFigure 4–5. To bring upthe dialog box, choose Graph Lines & Colors from the Display men

The Color Menus

The Color pop-up menus,Figure 4–6 , for the graticule and channelslet you choose the pattern and color of each. Press them to bring upthe options. The choices are the basic system colors; black, red, bluegreen, magenta, cyan, and yellow; and lighter patterns of the solidcolors: gray, light red, and so on. Colors appear as greys on a gray-scale monitor. Colors and greys can be printed as well as displayed, you have an appropriate printer.

Other Controls

The Graticule buttons let you choose the form of the display grid.Click to select a button — it is highlighted with a heavy border. You

can choose to have a dot graticule (the default setting, no graticule aall, or a line graticule.

The Background buttons let you choose whether the background ofthe voltammogram is white or black. Click to select a button — it ishighlighted with a heavy border.

The Line type buttons for each channel give you the choice ofdisplaying the data points joined by lines, as unjoined dots(individual data points), or as a solid ll. Click to select a button —

is highlighted with a heavy border. A continuous line is the defaultfor EChem.

Graticule buttons

Background buttons

Line type buttons

Figure 4–6The Color pop-up menu


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Overlay Display Settings

By default, the voltammogram shown on the active page is colored black and those on the overlaid pages are in gray. You can changecolors and patterns of the active and overlaid voltammograms bychoosing Overlay Display Settings… from the Display menu. TheOverlay Display Settings dialog box will be displayed. The controls ithe Overlay Display Settings dialog,Figure 4–7 , work in the sameway as those in the ordinary Display Settings dialog,Figure 4–5, except that they dene the settings for overlaid data only.

Navigating

EChem stores sweeps of data as if they were pages in a pad of paper.The numbered Page buttons along the bottom of the EChem windowand the Page Corner controls (the ‘dog-ears’) at the bottom right ofthe data display area allow you to move through multiple pages of aEChem le. The highlighted Page button indicates the page of data being viewed, the active page.

Click the upper folded corner of the Page Corner controls to move apage right, and the lower corner to move left. You can also move apage left or right by pressing, respectively, the left and right arrow

keys on the keyboard. Hold down the Command key (Macintosh), orControl key (Windows PC), while pressing the left or right arrow keyto go to the beginning or the end of the le (the rst or last numberedpages).

Colour pop-upmenu

Line typebuttons

Blankpage

Activepage

Page Corner controls

Scrolling buttons

Figure 4–7The Overlay Display Settingsdialog.


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To go to a specic page, choose Go To Page… from the Display meor type Command-G (Macintosh) or Control-G (Windows PC). TheGo To Page dialog box appears (Figure 4–8): and you type thenumber of the page in the text entry box (which will be selected) anclick the OK button (or press Return or Enter).

You can also click a numbered Page button to go to that page. If theare too many pages to show all the buttons along the bottom of the

window, then left and right arrow buttons will appear at either side:click them to move a page left or right, or press them to scroll left orright through many pages.

Overlaying PagesYou can overlay pages of data recorded at different times or underdifferent conditions one atop the other.

Choose the Show Overlay from the Display menu. The nominatedpages selected can be seen through the active page as if eachvoltammogram were on a pad of transparent plastic sheets. The mencommand then changes to Hide Overlay and only the active page isvisible. These commands turn the page overlaying display on or off,respectively, and do not affect which particular pages have beenselected for overlay.

To overlay all pages, choose Overlay All from the Display menu, ortype Command-A (Macintosh), or Control-A (Windows). The data iall pages appears, drawn atop each other. By default, the data shownon the active page is black and other, overlaid, pages are in gray(these settings can be changed). To remove all pages from the overlachoose Overlay None from the Display menu, or type Command-H(Macintosh), or Control-H (Windows PC). Only the active pageremains visible, and none of the others is selected for overlaying.

Figure 4–8The Go To Page dialog box.


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Using the Page Buttons

The Page buttons along the bottom of the main window indicate thestatus of pages. The active page is highlighted; Pages selected foroverlaying have icons containing black rectangles and those notselected have icons with gray rectangles.

As mentioned, you can click a numbered Page button to go to thatpage. The active page does not need to be included in overlaying,since it will always appear (so that you can, for instance, quicklycheck a set of overlays against a set of reference pages which are notthemselves overlaid). Command-click (Macintosh), or Control-click(Windows PC), or double-click a Page button to add the page to orremove it from the set of overlaid pages. Option-click (Alt-click) aPage button to hide all pages except the one whose icon was clicked.Press and hold a Page button to activate the pop-up menu whichduplicates the various overlay and navigation functions (Figure 4–10

The Scale of Overlaid Pages

When you overlay pages with different vertical ranges, data on otherpages is automatically shown scaled to the range of the active page.However in IE vs t, and I vs t, modes the horizontal time axis is not

Selectedpage

Includedin overlay

Not includedin overlay

Blankpage

In case you press rather than click the Page button

Command-click (Control-click) or double-clickCommand-click (Control-click) or double-clickOption-click (Alt-click)

Click and hold the mouse down

Figure 4–10The Page Button menu

Figure 4–9Overlaying pages.


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scaled and the overlaid pages, which could have different time basesmay not be shown to scale.

The Zoom Window

With the Zoom window, you can look at a small section of data ingreat detail. To zoom in on a data selection, drag to select an area ofinterest in the main window, and then choose Zoom Window fromthe Windows menu: the Zoom window appears (Figure 4–11).

You can make a further selection in the data display area of the Zoomwindow: this automatically zooms in further on that data. If theselection contains less than four data points, the Zoom window willappear gray. If this happens, you should reselect an area in the mainEChem window.

Data Display The Zoom window does not have the Display pop-up menu to switc between I vs E, or IE vs t etc., but has the other controls (Marker anpage buttons etc.) of the Main window.

First make a selection of the voltammogram to beenlarged, then choose the Zoom Window commandfrom the Windows menu

Figure 4–11The Zoom Window


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In IE vs t display mode, if the selection covers only one channel, thenonly one channel is displayed, and the separator handle is dimmed(see Figure 4-12). If the selection covers two channels, then by defauthe channels are overlaid, but as in the Main window, double-clickingor dragging the channel separator handle will separate them.Channel overlaying is independent of that in the Main window: you

can have the channels separate there and overlaid in the Zoomwindow, for instance.

The scale of the vertical axis of each channel can be independentlydragged or stretched for optimum data display, just as in the mainEChem window.

When moving between pages, the selection area remains the samewith regard to the raw data (and will remain in the same relativeposition in the EChem window).

The Marker from the Main window knows about the Marker in theZoom window — moving it onto a voltammogram in one windowwill do the same in the other, double-clicking it will send it to its lair

Drag the channel separator (the shortblack bar) up and down, to the

desired position or double click theseparator to overlay the channels —top picture.

The channel separator in overlay mode.Double click to show separate channels.Figure 4–12

The Zoom Window in IE vs tdisplay mode


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— and the Page Comment button will bring up the Page Commentwindow for the active page.

As you move the pointer across the data display area, the Cursortracks the displayed data, and the current (i) and potential (E)readings at the tracking point are indicated in the Cursor panel.

Printing the Zoom Window

When the Zoom window is active, then when Print… is chosen fromthe File menu, the contents of the Zoom window are printed, after thappropriate dialog boxes have been dealt with. The printed page isheaded with the window title and the number of the EChem page.

Display and Printer ResolutionEChem allows a exible data display, so that the display can berescaled and resized. The controls are not difcult to get used to,especially since the axes are always visible, but they may make thevoltammogram look abnormal if you expect it to have the same sizeand aspect ratio of a standard chart or XY recorder.

The screen display on a monitor is generally about 72 dots per inch,so the apparent resolution is not that good if the display is kept smalThe signal might appear jagged and unresolved on a small screen.However, the resolution of the recorded data is independent of theresolution of the display: sampled data is always recorded at 12 bit(0.024%) delity at each sensitivity setting. The one important rule to record your data at the maximum sensitivity (gain) that will keepyour voltammogram within the full scale range.

High-resolution printing will show the selected voltammogramaccurately. A print-out might not appear as smooth as the pen outputof a standard pen recorder if you are using a low resolution dotmatrix printer. To get high quality output you should use a laserprinter or inkjet printer with a resolution of 300 dpi or greater. Laserprinters that use Adobe PostScript® are recommended for maximumquality output.

It is important to check display settings carefully when examining adata, to be sure that what you are looking at is what you think you


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are looking at, especially if the settings on your machine might have been altered. A trace may end up looking very strange if it has beenstretched vertically or had an inappropriate baseline subtracted.

Making MeasurementsWhen you have nished recording you can make direct or relativemeasurements from the voltammogram (or amperomogram).

When the pointer is over the data display area, the Cursor tracks thevoltammogram,Figure 4–13. In this case, The Cursor panel shows thecurrent, potential, and time coordinates at the cursor location

The Cursor only gives discrete measurements, jumping from datapoint to data point (you can see this more clearly in the Zoom

window). It cannot provide a reading on the line that is drawn between the individual data points.

Using the MarkerThe Marker can be found in its ‘lair’, a box at the bottom left of theEChem window. It is used to set a particular data point as a zeroreference point, so that relative measurements can be made withrespect to that point,Figure 4–14. To set the Marker, drag it from its

Current, potential and time (I, E and t)cursor coordinates

The cursor is attached tothe trace but follows thepointer.

The pointer is positioned with the mouse.

Figure 4–13Use of the Pointer and Cursor.


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lair into the voltammogram — it will lock onto the voltammogramwhen you release the mouse button. Option-drag the Marker toposition it the anywhere on the screen. Use the display in the Cursorpanel to help to select a data point. If you need ner control of theMarker position, use the Zoom window to look at a selection in mordetail: the Marker is duplicated there, and can more easily be

assigned to a particular data point.Double-clicking the Marker or clicking its box at the bottom left of EChem (or Zoom) window sends it back t

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