Electroanalytical Chemistry

Оглавление

Gary A. Mabbott. Electroanalytical Chemistry

Table of Contents

List of Tables

List of Illustrations

Guide

Pages

Electroanalytical Chemistry. Principles, Best Practices, and Case Studies

Copyright

Preface

1 Basic Electrical Principles

1.1 Overview

1.2 Basic Concepts

1.2.1 Volt Defined

1.2.2 Current Defined

1.2.3 Oxidation and Reduction

1.2.4 Current and Faraday's Law

1.2.5 Potential, Work, and Gibbs' Free Energy Change

1.2.6 Methods Based on Voltage Measurement Versus Current Measurement

1.3 Electrochemical Cells. 1.3.1 Electrodes

1.3.2 Cell Resistance

1.3.3 Supporting Electrolyte

1.4 The Electrified Interface or Electrical Double Layer

1.4.1 Structure of the Double Layer

1.4.2 The Relationship Between Double Layer Charge and the Potential at the Electrode Interface

1.5 Conductance

1.6 Mass Transport by Convection and Diffusion

1.7 Liquid Junction Potentials

Problems

References

2 Potentiometry of Oxidation–Reduction Processes. 2.1 Overview

2.2 Measuring “Open Circuit” Potentials

2.3 Solution Redox Potential

2.3.1 The Development of a Charge Separation

2.3.2 The Nernst Equation

2.3.3 Formal Potential

2.3.4 Active Metal Indicator Electrodes

2.3.4.1 An Active Metal Electrode of the First Kind

2.3.4.2 An Active Metal Electrode of the Second Kind

2.3.4.3 Reference Electrodes

2.3.4.4 The Standard Hydrogen Electrode

2.3.4.5 Comparing Reference Electrodes

2.3.5 Redox Titrations

2.3.6 Oxidation–Reduction Potential (ORP) or EH

2.3.7 Environmental Applications of Redox Measurements. 2.3.7.1 Soil EH and pH

2.3.7.2 Applications to Fermentation Processes

2.3.7.3 Applications to Sterilization

Problems

References

3 Potentiometry of Ion Selective Electrodes. 3.1 Overview

3.2 Liquid Membrane Devices. 3.2.1 Selective Accumulation of Ions Inside an Organic Liquid

3.2.2 Theory of Membrane Potentials

Example 3.1

3.2.3 Liquid Membrane Ionophores

3.3 Glass Membrane Sensors. 3.3.1 History of the Development of a Glass Sensor of pH

3.3.2 Glass Structure and Sensor Properties

3.3.3 Selective Ion Exchange Model

3.3.4 The Combination pH Electrode

3.3.5 Gas‐Sensing Electrodes

Example 3.2

3.4 Crystalline Membrane Electrodes

3.5 Calibration Curves and Detection Limits

Example 3.3

3.6 A Revolutionary Improvement in Detection Limits

3.7 More Recent Ion Selective Electrode Innovations

3.7.1 The Function of the Inner Reference Electrode

3.7.2 All Solid‐State Reference Electrodes

3.7.3 Eliminating the Inner Reference Electrode

3.7.4 Super‐Hydrophobic Membranes

3.8 Ion Selective Field Effect Transistors (ISFETs)

3.9 Practical Considerations. 3.9.1 Ionic Strength Buffers

3.9.2 Potential Drift

Problems

REFERENCES

4 Applications of Ion Selective Electrodes. 4.1 Overview

4.2 Case I. An Industrial Application

4.2.1 Will the Sample Concentrations Be Measurable?

4.2.2 Ionic Strength Adjustment Buffer

4.2.3 Sample Pretreatment

4.2.4 Salt Bridges

4.2.5 Calibration

4.2.6 Temperature Control

4.2.7 Signal Drift

4.2.8 Validating the Method

Example 4.1

4.2.9 Standard Additions for Potentiometric Analysis

4.3 Case II. A Clinical Application

4.4 Case III. Environmental Applications

4.4.1 US EPA Method for Nitrate Determination by ISE

4.4.2 Field Measurements

4.5 Good Lab Practice for H Electrode Use

4.5.1 Electrode Maintenance

4.5.2 Standard Buffers

4.5.3 Influence of Temperature on Cell Potentials

4.5.4 Calibration and Direct Sample Measurement

4.5.5 Evaluating the Response of a pH Electrode

4.5.6 Calibrating a Combination Electrode and pH Meter

4.5.7 Low Ionic Strength Samples

4.5.8 Samples Containing Soil, Food, Protein or Tris Buffer

4.5.9 pH Titrations

4.5.10 Gran Plots

Problems

References

5 Controlled Potential Methods. 5.1 Overview

5.2 Similarities between Spectroscopy and Voltammetry

5.3 Current is a Measure of the Rate of the Overall Electrode Process

5.3.1 Rate of Electron Transfer

5.3.2 The Shape of the Current/Voltage Curve

5.3.3 Rate of Mass Transport

5.3.4 Electrochemical Reversibility

5.3.5 Voltammetry at Stationary Electrodes in Quiet Solutions

5.3.5.1 Potential Step Experiments: Chronoamperometry

Example 5.1

5.3.5.2 Linear Voltage Scan: Cyclic Voltammetry (CV)

Example 5.2

Example 5.3

5.4 Methods for Avoiding Background Current

5.5 Working Electrodes. 5.5.1 Mercury Electrodes

5.5.2 Solid Working Electrodes

5.5.2.1 Types of Carbon Electrode Surfaces

5.5.2.2 The Role of Carbon Electrode Surface Chemistry

5.5.2.3 Working Electrode Surface Preparation

Example 5.4

5.5.2.4 Carbon Fiber Electrodes

5.5.2.5 Novel Carbon Electrode Materials

5.5.3 Ultramicroelectrodes

Example 5.5

5.5.4 Fast Scan CV

5.6 Pulse Amperometric Detection

5.7 Stripping Voltammetry

5.8 Special Applications of Amperometry. 5.8.1 Flow‐Through Detectors

5.8.2 Dissolved Oxygen Sensors

5.8.3 Enzyme Electrodes

5.8.4 Karl Fisher Method for Moisture Determination

Example 5.6

5.9 Ion Transfer Voltammetry

Problems

References

6 Case Studies in Controlled Potential Methods. 6.1 Overview

6.2 Case I. Evaluating the Formal Potential and Related Parameters

6.3 Case II. Evaluating Catalysts – Thermodynamic Considerations

6.4 Case III. Studying the Oxidation of Organic Molecules

6.5 Case IV. Evaluating Catalysts – Kinetic Studies

References

7 Instrumentation. 7.1 Overview

7.2 A Brief Review of Passive Circuits

Example 7.1

7.3 Operational Amplifiers

7.3.1 Properties of an Ideal Operational Amplifier

7.3.2 The Voltage Follower

7.3.3 Current Follower or Current‐to‐Voltage Converter

Example 7.2

7.3.4 Inverter or Simple Gain Amplifier

7.3.5 A Potentiostat for a Three‐Electrode Experiment

7.4 Noise and Shielding

7.5 Making Electrodes and Reference Bridges. 7.5.1 Voltammetric Working Electrodes

7.5.2 Reference Electrodes

Problems

References

Appendix A Ionic Strength, Activity, and Activity Coefficients

Example A.1

References

Appendix B The Nicolsky–Eisenman Equation

References

Appendix C The Henderson Equation for Liquid Junction Potentials1

Reference

Note

Appendix D Standard Electrode Potentials for Some Selected Reduction Reactions

References

Appendix E The Nernst Equation from the Concept of Electrochemical Potential1

Reference

Note

Solutions to Problems

Index

Chemical Analysis

WILEY END USER LICENSE AGREEMENT

Отрывок из книги

Gary A. Mabbott

One of the growing areas in which electrochemical methods will continue to play an important role is in sensor technology. Electrochemical devices are relatively simple in terms of instrumentation and can be miniaturized. Both of these attributes help keep their costs down and make them candidates for applications such as remote sensors, personal health care monitors, and implantable devices. Some of the newer developments in both ion selective electrodes and voltammetric devices are making these sensors more selective, more robust, applicable to a wider range of analytes, and capable of lower detection limits. As simple as they may be in terms of associated hardware, these devices take advantage of a range of physical and chemical phenomena and are notable intellectual achievements. Advances in this area will require a firm grasp of the underlying science, imagination and hard work, but the possibilities are plentiful.

.....

(1.17)

where ci is the molar concentration of an ion with charge, zi, summed over all ions. In addition to the effect on activity of the analyte, the mismatch between the sample solution and reference solution in concentration and type of ions making up the supporting electrolyte contributes to an error called the liquid junction potential. (That phenomenon is addressed latter in this chapter.) Consequently, it is important to control the ionic strength. This is often done by the addition of a solution of a high concentration of electrolyte, known as an ionic strength adjustment buffer. Whenever that is not practical, an effort is made to keep the ionic strength constant among all the sample and calibration standards. (Ion activities and activity coefficients are discussed in Appendix A.)

.....