FUNDAMENTALS OF ELECTRO- ANALYTICAL CHEMISTRY Paul Monk Manchester Metropolitan University, Manchester, UK JOHN WILEY & SONS LTD Chichester New Weinheim Brisbane Toronto Singapore York FUNDAMENTALS OF ELECTROANALYTICAL CHEMISTRY Analytical Techniques in the Sciences (AnTS) Series Editor: David J. Ando, Consultant, Dartford, Kent, UK A series of open learning/distance learning books which covers all of the major analytical techniques and their application in the most important areas of physical, life and materials sciences. Titles Available in the Series Analytical Instrumentation: Performance Characteristics and Quality Currell, University of the West of England, Bristol, UK Graham Fundamentals of Electroanalytical Chemistry Paul M. S. Monk, Manchester Metropolitan University, Manchester, UK Forthcoming Titles Polymer Analysis Barbara H. Stuart, University of Technology, Sydney, Australia Environmental Analysis Roger N. Reeve, University of Sunderland, UK FUNDAMENTALS OF ELECTRO- ANALYTICAL CHEMISTRY Paul Monk Manchester Metropolitan University, Manchester, UK JOHN WILEY & SONS LTD Chichester New Weinheim Brisbane Toronto Singapore York Copyright 0 2001 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 SSQ, England Telephone 1243 779777 (+44) Email (for orders and customer service enquiries): [email protected] Visit Home Page on www.wileyeurope.com or www.wiley.com OUT Reprinted August 2002, July 2005 All Rights Resewed. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except under the terms of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London WIT 4LP, UK, without the permission in writing of the Publisher. Requests to the Publisher should be addressed to the Permissions Department, John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 SSQ, England, or emailed to [email protected], or faxed to 1243 77057 I. (+44) This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the Publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought. Other WiIq Editorial Onces John Wiley & Sons Inc., 1 I I River Street, Hoboken, NJ 07030, USA Jossey-Bass, 989 Market Street, San Francisco, CA 94103-1741, USA Wiley-VCH Verlag GmbH, Boschstr. 12, D-69469 Weinheim, Germany John Wiley & Sons Australia Ltd, 33 Park Road, Milton, Queensland 4064, Australia John Wiley & (Asia) Pte Ltd, 2 Clementi Loop #02-01, Jin Xing Distripark, Singapore 129809 Sons John Wiley & Sons Canada Ltd, 22 Worcester Road Etobicoke, Ontario, Canada M9W ILI Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Library of Congress CalaIoging-in-Publication Dam Paul M. S. Monk, Electroanalytical chemistry / Paul Monk. p. cm. -(Analytical techniques in the sciences) Includes bibliographical references and index. ISBN 0-471-88036-1 (alk. paper)- ISBN 0-471-88140-6 (ak. paper) I. Electrochemical analysis. 1. Title. 11. Series. QDI 15.M58 2001 543'.087 I-dc21 00-043577 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 10: 0-471-88140-6 (P/B) ISBN 13: 978-0-471-88140-7 (PIB) ISBN 10: 0-471-88036-1 (We) ISBN 13: 978-0-471-88036-3( H /B) Typeset in 10/12 pt Times by Laser Words, (India) Ltd Printed and bound in Great Britain by Antony Rowe Ltd. Chippenham, Wiltshire. This is printed on acid-free paper responsibly manufactured from sustainable foreshy book in which at least two trees are planted for each one used for paper production. Contents Series Preface xi Preface xiii Acronyms, Abbreviations and Symbols xv About the Author xxi 1 Explanatory Foreword 1 1.1 Electroanalysis 1 1.2 Nomenclature and Terminology (IUPAC and Non-IUPAC) 3 1.3 This Book 9 Reference 10 2 Introductory Overview and Discussion of Experimental Methodology 11 2.1 Overview of the Differences between Equilibrium and Dynamic Measurements 12 2.2 The Magnitude of the Current: Rates of Electron Transfer, Mass Transport, and their Implications 17 2.3 The Implications of Using Diffusive or Convective Control 23 Reference 24 3 Equilibrium Measurements: ‘Frustrated’ Equilibrium with No Net Electron Transfer 25 3.1 Introduction: What is ‘Equilibrium’? Concepts of ‘Frustrated’ Equilibrium 26 vi Fundamentals of Eiectroanalytical Chemistry 3.2 Revision: emf, Electrode Potentials and the SHE 29 3.2.1 Terminology and Symbolisms 29 3.2.2 Reference Electrodes 33 3.3 The Nernst Equation and its Permutations 36 3.3.1 Limitations of the Nernst Equation 42 3.4 Differences between Concentration and Activity 44 3.4.1 Brief Discourse on Ion-Ion Interactions 44 3.4.2 Activities 47 3.4.3 Activity Coefficients 48 3.4.4 Revision of Debye-Huckel Theory 50 3.5 Applications Based on Calculations with the Nernst Equation 57 3.5.1 pH Determination and the pH Electrode 57 3.5.2 Ion-Selective Electrodes 60 3.5.3 Potentiometric Determination of Solubility Constants 69 3.6 Causes and Treatment of Errors 71 3.6.1 Current Passage through a Cell Causing Internal Compositional Changes 72 3.6.2 Current Passage through Reference Electrodes 73 3.6.3 Determination of Concentration when the Mean Ionic Activity Coefficient is Unknown 74 3.6.4 Cell Design and the Effects of ‘IR Drop’ 74 3.6.5 Adational Sources of Potential Owing to Ionic Transport and Junction Potentials 75 4 Potentiometry: True Equilibrium and Monitoring Systems with Electron lkansfer 85 4.1 Introduction to Potentiometry 86 4.1.1 Redox Titrations: End Points and Shapes of Curves 86 4.1.2 Determination of Equilibrium Constants and Solubility Constants 96 4.2 Redox Indicators 100 4.3 Treatment of Errors 103 4.3.1 Routine Errors 103 4.3.2 Errors Caused by Low Precision of Volume Determination: Use of Gran Plots 103 4.3.3 Errors Caused by Poor ISE Selectivity 105 5 Coulometry 107 5.1 Introduction to Coulometry and Faraday’s Laws 108 5.1.1 Faradaic and Non-Faradaic Charge 115 Contents vii 5.1.2 The Effects of Absorption, Capacitance and the Electrode Double-Layer 117 5.2 Stripping 122 5.3 Microelectrodes 125 5.4 Introduction to Electron Mediation 127 5.5 Treatment of Errors 128 6 Analysis by Dynamic Measurement, A: Systems under Diffusion Control 131 6.1 Experimental Introduction to Dynamic Electrochemistry 132 6.2 Chronoamperometry: Current Determined with Time 136 6.2.1 The Nernst Layer (‘Depletion’ Layer) 137 6.2.2 The Cottrell Equation 141 6.3 Polarography at Hg Electrodes 142 6.3.1 The Polarographic Experiment 143 6.3.2 Polarography: the Dropping-Mercury Electrode 144 6.3.3 Treatment of Polarographic Data: Obtaining E1/2 and its Use 151 6.3.4 Determination of Equilibrium Constants: Shifts in El12 on Complexation 153 6.4 Linear-Sweep and Cyclic Voltammetry at Solid Electrodes 156 6.4.1 The Randles-SevEik Equation 162 6.4.2 The Effect of Slow Electron Transfer: Semiconducting Electrodes 166 6.4.3 Quantification of Diffusion Phenomena 168 6.4.4 Mechanistic Data from Voltammetry 169 6.5 Improving Sensitivity: Pulse Methods 176 6.5.1 Normal Pulse Voltammetry 176 6.5.2 Differential Pulse Voltammetry 179 6.5.3 Square-Wave Pulse Voltammetry 182 6.6 Stripping Voltammetry 185 6.7 The Glucose Sensor: a Worked Example of Voltammetric Analysis 188 6.8 Causes and Treatment of Errors 191 6.8.1 Polarographic ‘Peaks’ 191 6.8.2 IR Drop: the Luggin Capillary 192 7 Analysis by Dynamic Measurement, B: Systems under Convection Control 195 7.1 Introduction to Convective Systems 196 ... Vlll Fundamentals of Electroanalytical Chemistry 7.2 The Rotated Disc Electrode 197 7.2.1 Discussion of the Experiment 197 7.2.2 The Levich Equation 202 7.3 How Cells, Channel Electrodes and Wall-Jet Electrodes 210 7.3.1 Flow Cells and Channel Electrodes 210 7.3.2 The Wall-Jet Electrode 215 7.4 The Rotated Ring-Disc Electrode 218 7.5 Rate Constants of Electron Transfer 223 7.5.1 The Tafel Approach to Electrode Kinetics 225 7.5.2 The Butler-Volmer Approach 226 7.5.3 Koutecky-Levich Plots and Measurement of the Rates of Electron Transfer 232 7.6 Causes and Treatment of Errors 234 Reference 236 8 Additional Methods 237 8.1 Spectroelectrochemistry 238 8.1.1 Introduction: What is Spectroelectrochemistry? 238 8.1.2 Electrochemical UV-Visible Spectroscopy 239 8.1.3 Electrochemical EPR Spectroscopy 247 8.2 Electroanalytical Measurements Involving Impedance 253 8.2.1 What is Impedance? 253 8.2.2 Impedances of Real Cells: Quantification of Diffusion Phenomena and the Warburg Impedance 262 8.3 Causes and Treatment of Errors 270 8.3.1 Discontinuities in an OTE Conductor 270 8.3.2 Total Internal Reflection in UV-Visible Spectroscopy 270 8.3.3 Large Absorbances and the Optical Band Edge 27 1 8.3.4 Stray EPR Absorptions 273 Reference 274 9 Electrode Preparation 275 9.1 Preparation and Characterization of Solid Electrode Surfaces 276 9.1.1 Cleaning Electrode Surfaces 276 9.1.2 Manufacturing Electrodes 280 9.1.3 Making Reference Electrodes 284 9.2 Microelectrodes 286 9.3 Screen-Printed Electrodes 287 Reference 288