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Principles and Practice of Analytical Chemistry


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Principles and Practice
of Analytical Chemistry
Fourth Edition
F.

w. FIFIELD and D. KEALEY
Kingston University

SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.


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First edition 1975
Second edition 1983
Third edition 1990
This edition 1995

© 1995 Springer Science+Business Media Dordrecht
Originally published by Chapman & HaU in 1995
Typeset in 10/12 pt Times by AFS Image Setters Ltd, Glasgow
ISBN 978-1-4613-5912-8
ISBN 978-1-4615-2179-2 (eBook)

DOI 10.1007/978-1-4615-2179-2
Apart from any fair dealing for the purposes of research or private study, or
criticism or review, as permitted under the UK Copyright Designs and
Patents Act, 1988, this publication may not be reproduced, stored, or
transmitted, in any form or by any means, without the prior permission in
writing of the publishers, or in the case of reprographic reproduction only
in accordance with the terms of the licences issued by the Copyright
Licensing Agency in the UK, or in accordance with the terms of licences
issued by the appropriate Reproduction Rights Organization outside the
UK. Enquiries concerning reproduction outside the terms stated here
should be sent to the publishers at the Glasgow address printed on this
page.
The publisher makes no representation, express or implied, with regard
to the accuracy of the information contained in this book and cannot
accept any legal responsibility or liability for any errors or omissions that
may be made.
A catalogue record for this book is available from the British Library
Library of Congress Catalog Card Number: 94-74246

00 Printed on acid-free text paper, manufactured in accordance with
ANSIjNISO Z39.48-1992 (Permanence of Paper).


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Contents
Preface
Acknowledgements

ix

Xl

CHAPTER 1 INTRODUCTION
The scope of analytical chemistry. The function of analytical chemistry.
Analytical problems and their solution. The nature of analytical
methods. Trends in analytical methods and procedures. Glossary of
terms.

CHAPTER 2

2.1
2.2
2.3

THE ASSESSMENT OF ANALYTICAL DATA

Definitions and basic concepts
The nature and origin of errors
The evaluation of results and methods

14
14
16

18

The reliability of measurements. The analysis of data. The application
of statistical tests. Limits of detection. Quality control charts.
Standardization of analytical methods. Chemometrics.


CHAPTER 3 pH, COMPLEXATION AND SOLUBILITY
EQUILIBRIA

3.1

Chemical reactions in solution

3.2

Solvents in analytical chemistry

37
38

Equilibrium constants. Kinetic factors in equilibria.
42

Ionizing solvents. Non-ionizing solvents.

3.3

Acid-base equilibria

43

Weak acid and weak base equilibria. Buffers and pH control. The pH
of salt solutions.

3.4


Complexation equilibria

50

The formation of complexes in solution. The chelate effect.

3.5

Solubility equilibria

53

Solubility products.

CHAPTER 4 SEPARATION TECHNIQUES
4.1
Solvent extraction

55
56

Efficiency of extraction. Selectivity of extraction. Extraction systems.
Extraction of uncharged metal chelates. Methods of extraction.
Applications of solvent extraction.

4.2

Chromatography

75


4.2.1 Gas chromatography. 4.2.2 High performance liquid chromatography. 4.2.3 Supercritical fluid chromatography. 4.2.4 Thin-layer
chromatography. 4.2.5 Ion-exchange chromatography. 4.2.6 Gelpermeation chromatography.

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CONTENTS

VI

4.3

Electrophoresis

164

Factors affecting ionic migration. Effect of temperature, pH and ionic
strength. Electroosmosis. Supporting medium. Detection of separated
components. Applications of tradional zone electrophoresis. High performance capillary electrophoresis.

CHAPTER 5 TITRIMETRY AND GRAVIMETRY
5.1
Titrimetry

184
184


Definitions. Titrimetric reactions. Acid-base titrations. Applications
of acid-base titrations. Redox titrations. Applications of redox
titrations. Complexometric titrations. EDTA. Applications of EDTA
titrations. Titrations with complexing agents other than EDT A.
Precipitation titrations.

5.2

Gravimetry

211

Precipitation reactions. Practical gravimetric procedures. Applications
of gravimetry.

CHAPTER 6 ELECTROCHEMICAL TECHNIQUES
6.1
Potentiometry

223
227

Electrode systems. Direct potentiometric measurements. Potentiometric titrations. Null-point potentiometry. Applications of potentiometry.

6.2

Polarography, stripping voltammetry and amperometric
techniques

243


Diffusion currents. Half-wave potentials. Characteristics of the DME.
Quantitative analysis. Modes of operation used in polarography.
The dissolved oxygen electrode and biochemical enzyme sensors.
Amperometric titrations. Applications of polarography and amperometric titrations.

6.3

Electrogravimetry and coulometry

257

Coulometry. Coulometry at constant potential. Coulometric titrations.
Applications of coulometric titrations.

6.4

Conductometric titrations

261

Ionic conductances.

CHAPTER 7 AN INTRODUCTION TO ANALYTICAL
SPECTROMETRY

267

Electromagnetic radiation. Atomic and molecular energy. The
absorption and emission of electromagnetic radiation. The complexity

of spectra and the intensity of spectral lines. Analytical spectrometry.
Instrumentation.

CHAPTER 8 ATOMIC SPECTROMETRY
8.1
Arc/spark atomic (optical) emission spectrometry

282
287

Instrumentation. Sample preparation. Qualitative and quantitative
analysis. Interferences and errors associated with the excitation process.
Applications of arc/spark emission spectrometry.

8.2

Glow discharge atomic emission spectrometry
Instrumentation. Applications.

294


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8.3

CONTENTS

VB


Plasma emission spectrometry

296

Instrumentation. Sample introduction for plasma sources. Analytical
measurements. Applications of plasma emission spectrometry.

8.4

Inductively coupled plasma-mass spectrometry
(ICP-MS)

304

Principles. Instrumentation. Applications.

8.5

Flame emission spectrometry

308

Instrumentation. Flame characteristics. Flame processes. Emission
spectra. Quantitative measurements and interferences. Applications
of flame photometry and flame atomic emission spectrometry.

8.6

Atomic absorption spectrometry


317

Absorption of characteristic radiation. Instrumentation. Sample
vaporization. Quantitative measurements and interferences. Atomic
fluorescence spectrometry.

8.7

X-ray emission spectrometry

331

X-ray processes. Instrumentation. Applications of X-ray emission
spectrometry.

CHAPTER 9 MOLECULAR SPECTROMETRY

351

9.1

361

Visible and ultraviolet spectrometry
Poly atomic organic molecules. Metal complexes. Qualitative analysis
- the identification of structural features. Quantitative analysis absorptiometry. Choice of colorimetric and spectrophotometric
procedures. Fluorimetry. Applications of UV/visible spectrometry and
fluorimetry.

9.2


Infrared spectrometry

377

Diatomic molecules. Poly atomic molecules. Characteristic vibration
frequencies. Factors affecting group frequencies. Qualitative analysis
- the identification of structural features. Quantitative analysis.
Sampling procedures. Applications of infrared spectrometry.

9.3

NucIear magnetic resonance spectrometry (nmr)

393

Instrumentation. The nmr process. Chemical shift. Spin-spin coupling.
Carbon-13 nmr. Pulsed Fourier transform nmr (ft-nmr). Quantitative
analysis - the identification of structural features. Quantitative analysis.
Applications of nmr spectrometry.

9.4

Mass spectrometry

425

Instrumentation. Principle of mass spectrometry. Characteristics and
interpretation of molecular mass spectra. Applications of mass spectrometry.


9.5

Spectrometric identification of organic compounds

436

CHAPTER 10 RADIOCHEMICAL METHODS IN ANALYSIS

447

10.1

448

Nuclear structure and nuclear reactions
Decay reactions. The kinetics of decay reactions. Bombardment
reactions and the growth of radioactivity.

10.2

Instrumentation and measurement of radioactivity
Radiation detectors. Some important electronic circuits. The statistics
of radioactive measurements.

455


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10.3

CONTENTS

Analytical uses of radionucleides

465

Chemical pathway studies. Radioisotope dilution methods. Radioimmunoassay. Radioactivation analysis. Environmental monitoring.

CHAPTER 11 THERMAL TECHNIQUES
11.1
Thermogravimetry

475
477

Instrumentation. Applications ofTG.

11.2

Differential thermal analysis (DTA)

482

Instrumentation. Applications of DTA

11.3


Differential scanning calorimetry (DSC)

489

Instrumentation. Applications of DSC. DTA and DSC.

11.4

Thermomechanical analysis (TMA) and dynamic
mechanical analysis (DMA)

493

Instrumentation. Applications of TMA. Dynamic mechanical analysis.

11.5

Pyrolysis - gas chromatography

497

Instrumentation.

CHAPTER 12 OVERALL ANALYTICAL PROCEDURES AND
THEIR AUTOMATION
12.1
Sampling and sample pretreatment

504


504

Representative samples and sample storage. Sample concentration and
clean-up: solid phase extraction.

12.2

Examples of analytical problems and procedures

509

1: Evaluation of methods for the determination of fluoride in water
samples. 2: Analysis ofa competitive product. 3: The assessment ofthe
heavy metal pollution in a river estuary. 4: The analysis of
hydrocarbon products in a catalytic reforming study.

12.3

The automation of analytical procedures.

519

The automation of repetitive analysis. Constant monitoring and on
line analysis. Laboratory robotics.

CHAPTER 13 THE ROLE OF COMPUTERS AND MICROPROCESSORS IN ANALYTICAL CHEMISTRY
13.1
Introduction

528

528

Instrument optimization. Data recording and storage. Data processing
and data analysis (chemometrics). Laboratory management. Expert
systems.

13.2

Computers and microprocessors

534

Mini- and microcomputers. Microprocessors.

13.3
13.4

Instrument-computer interfaces
The scope of microprocessor control and computers in
analytical laboratories
1.
2.
3.
4.

Index

537
542


A microprocessor-controlled potentiometric titrator.
An infrared spectrometer interfaced to a dedicated microcomputer.
A computing integrator for chromatographic analysis.
A microprocessor-based X-ray or ')I-ray spectrometer.

551


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Preface to the fourth edition

There have been significant advances in both analytical instrumentation and
computerised data handling during the five years since the third edition was
published in 1990.
Windows-based computer software is now widely available for instrument
control and real-time data processing and the use of laboratory information
and management systems (LIMS) has become commonplace. Whilst most
analytical techniques have undergone steady improvements in instrument
design, high-performance capillary electrophoresis (HPCE or CE) and twodimensional nuclear magnetic resonance spectrometry (2D-NMR) have
developed into major forces in separation science and structural analysis
respectively. The powerful and versatile separation technique of CE promises
to rival high-performance liquid chromatography, particularly in the separation of low levels of substances of biological interest. The spectral information provided by various modes of 2D-NMR is enabling far more complex
molecules to be studied than hitherto. The electrophoresis section of
chapter 3 and the NMR section of chapter 9 have therefore been considerably
expanded in the fourth edition along with a revision of aspects of atomic
spectrometry (chapter 8). New material has been included on fluorescence
spectrometry (chapter 9), the use of Kovats Retention Indices in gas chromatography (chapter 3) and solid phase extraction for sample cleanup and
concentration (chapter 12). Additions to high performance liquid chromatography (chapter 3) reflect the growing importance of chiral stationary
phases, solvent optimization and pH control, continuous regeneration cartridges for ion chromatography and HPLC-MS. Throughout the book there

have been numerous other changes and additions to enhance clarity and
presentation including a number of new or improved diagrams and some
additional worked examples on the statistical assessment of analytical data
(chapter 2).


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x

PREFACE TO FOURTH EDITION

The earlier editions have been widely used by both undergraduate and
postgraduate students of analytical chemistry, and the fourth edition should
continue to provide a sound basis for this readership. Industrial trainees and
those in related disciplines who require a knowledge of analytical chemistry
will find this a suitable text for reading and reference purposes.
We continue to benefit from discussions with many of our colleagues at
Kingston University, and particularly with Mr. P. 1. Haines whose knowledge
of thermal techniques has proved invaluable. The Publisher's reviewers and
users of the book continue to be a source of helpful and much appreciated
comments.

OK

FWF


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Acknowledgements

The following figures are reproduced with permission of the publishers:
Figure 7.8 from Christian and O'Reilly, Instrumental Analysis, 2nd edn.,
(1986) by permission of Allyn and Bacon, U.K.
Figure 10.17 from Cyclic GMP RIA Kit, Product Information 1976, by
permission of Amersham International, U.K.
Figures 8.14 and 8.15 from Date and Gray, Applications of Inductively
Coupled Plasma Mass Spectrometry (1989); figure 2.7 from Kealey,
Experiments in Modern Analytical Chemistry (1986); by permission of
Blackie, U.K.
Figure 8.24 from Manahan, Quantitative Chemical Analysis (1986) by permission of Brookes Cole, u.K.
Figures 8.27 and 8.28(a) and (b) from Allmand and Jagger, Electron Beam xray Microanalysis Systems, by permission of Cambridge Instruments Ltd.,
U.K.
Figures 4.20, 4.24(a) and (c) and 4.25 from Braithwaite and Smith,
Chromatographic Methods (1985); figures 11.2, 11.3, 11.4, 11.10 and 11.17
from Brown, Introduction to Thermal Analysis (1988); by permission of
Chapman and Hall.
Figures 11.23, 11.25 and 11.26 reprinted from Irwin, Analytical Pyrolysis
(1982) by courtesy of Marcel Dekker Inc. NY.
Figure 4.26(b) from Euston and Glatz, A new Hplc Solvent Delivery System,
Techn. Note 88-2 (1988) by permission of Hewlett-Packard, Waldbronn,
Germany.
Figures 4.10, 4.16, 6.4, 6.11(a) and (b), 6.12(a) and (b), 9.1, 9.4 and 9.50(a) and
(b) from Principles of Instrumental Analysis, 2nd edn., by Douglas Skoog
and Donald West, Copyright © 1980 by Saunders College/Holt, Rinehart
and Winston, Copyright © 1971 by Holt, Rinehart and Winston. Reprinted
by permission of Holt, Rinehart and Winston, CBS College Publishing;

xi



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XlI

ACKNOWLEDGEMENTS

figures 9.36, 9.37, 9.38, 9.39 and problems 9.6, 9.7 and 9.8 from Introduction
to Spectroscopy by Donald L. Pavia et al., Copyright © 1979 by W. B.
Saunders Company. Reprinted by permission ofW. B. Saunders Company,
CBS College Publishing.
Figure 8.39 from X-ray Microanalysis of Elements in Biological Tissue, by
permission of Link Systems, U.K.
Figure 4.24(b) from Williams and Howe, Principles of Organic Mass
Spectrometry (1972), by permission of McGraw-Hill Book Co. Ltd., U.K.
Figure 9.2(b) from SOXCjSSXC FTIR Spectrometer Brochure, by permission
of Nicolet Analytical Instruments, Madison, Wisconsin, U.S.A.
Figure 8.38 from Walinga, Advantages and Limitations of Energy Dispersive
X-ray Analysis, Phillips Bulletin (1972) by permission of NV Philips
Gloeilampenfabrieken, Netherlands.
Figure 8.25 from Brown and Dymott, The use of platform atomisation and
matrix modification as methods of interference control in graphite furnace
analysis, by permission of Philips Scientific and Analytical Equipment.
Figures 11.21 and 11.24 from Frearson and Haskins, Chromatography and
Analysis, Issue 7, (1989) by permission of RGC Publications.
Figures 4.14, 4.27, 9.2(a), 11.11, 11.20, 12.1 and 12.6(b) from Instrumental
Methods of Analysis, 7th edn., H. H. Willard, L. L. Merritt, J. A. Dean and
F. A. Settle, © 1988 Wadsworth, Inc. Reprinted by permission of the
publisher.

Figures 4.26(c), 4.31 and 13.3 from Snyder and Kirkland, Introduction to
Modern Liquid Chromatography, 2nd edn., (1979); 9.40(a), (b) and (c) from
Cooper, Spectroscopic Techniques for Organic Chemists (1980); 9.45
from Millard, Quantitative Mass Spectrometry (1978); 4.13, 4.14, 4.26(a),
4.28, 4.29(a), 4.32, 4.33, 4.36 and 4.38 from Smith, Gas and Liquid
Chromatography in Analytical Chemistry (1988); figures 4.35 and 13.2 from
Berridge, Techniques for the Automated Optimisation of Hplc Separations
(1985) reproduced by permission of John Wiley and Sons Limited; 11.1,
11.5,11.6,11.12,11.13,11.14,11.18 and 11.19 from Wendlandt, Thermal
Analysis, 3rd edn., (1986); reprinted by permission of John Wiley and Sons
Inc., all rights reserved.
Figure 10.16 from Chapman, Chemistry in Britain 15 (1979) 9, by permission
ofthe Royal Society of Chemistry.
Figure 6.4 is reprinted courtesy of Orion Research Incorporated, Cambridge,
Mass., U.S.A. 'ORION' is a registered trademark of Orion Research
Incorporated.


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Chapter 1
Introduction

Is there any iron in moon dust? How much aspirin is there in a headache
tablet? What trace metals are there in a tin of tuna fish? What is the purity
and chemical structure of a newly prepared compound? These and a host of
other questions concerning the composition and structure of matter fall
within the realms of analytical chemistry. The answers may be given by
simple chemical tests or by the use of costly and complex instrumentation.
The techniques and methods employed and the problems encountered are

so varied as to cut right across the traditional divisions of inorganic, organic
and physical chemistry as well as embracing aspects of such areas as biochemistry, physics, engineering and economics. Analytical chemistry is
therefore a subject which is broad in its scope whilst requiring a specialist
and disciplined approach. An enquiring and critical mind, a keen sense of
observation and the ability to pay scrupulous attention to detail are desirable
characteristics in anyone seeking to become proficient in the subject. However, it is becoming increasingly recognized that the role of the analytical
chemist is not to be tied to a bench using a burette and balance, but to
become involved in the broader aspects of the analytical problems which
are encountered. Thus, discussions with scientific and commercial
colleagues, customers and other interested parties, together with on-site visits
can greatly assist in the choice of method and the interpretation of analytical
data thereby minimizing the expenditure of time, effort and money.
The purpose of this book is to provide a basic understanding of the
principles, instrumentation and applications of chemical analysis as it is
currently practised. The amount of space devoted to each technique is based
upon its application in industry as determined in a national survey of
analytical laboratories. Some little used techniques have been omitted altogether. The presentation is designed to aid rapid assimilation by emphasizing
unifying themes common to groups of techniques and by including short
summaries at the beginning of each section.
1


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2

ANALYTICAL CHEMISTRY

THE SCOPE OF ANALYTICAL CHEMISTRY


Analytical chemistry has bounds which are amongst the widest of any
technological discipline. An analyst must be able to design, carry out, and
interpret his measurements within the context of the fundamental technological problem with which he is presented. The selection and utilization of
suitable chemical procedures requires a wide knowledge of chemistry, whilst
familiarity with and the ability to operate a varied range of instruments is
essential. Finally, an analyst must have a sound knowledge of the statistical
treatment of experimental data to enable him to gauge the meaning and
reliability of the results that he obtains.
When an examination is restricted to the identification of one or more
constituents of a sample, it is known as qualitative analysis, while an examination to determine how much of a particular species is present constitutes a
quantitative analysis. Sometimes information concerning the spatial arrangement of atoms in a molecule or crystalline compound is required or confirmation of the presence or position of certain organic functional groups is
sought. Such examinations are described as structural analysis and they may
be considered as more detailed forms of analysis. Any species that are the
subjects of either qualitative or quantitative analysis are known as analytes.
There is much in common between the techniques and methods used in
qualitative and quantitative analysis. In both cases, a sample is prepared for
analysis by physical and chemical 'conditioning', and then a measurement of
some property related to the analyte is made. It is in the degree of control
over the relation between a measurement and the amount of analyte present
that the major difference lies. For a qualitative analysis it is sufficient to be
able to apply a test which has a known sensitivity limit so that negative and
positive results may be seen in the right perspective. Where a quantitative
analysis is made, however, the relation between measurement and analyte
must obey a strict and measurable proportionality; only then can the amount
of analyte in the sample be derived from the measurement. To maintain this
proportionality it is generally essential that all reactions used in the preparation of a sample for measurement are controlled and reproducible and that
the conditions of measurement remain constant for all similar measurements.
A premium is also placed upon careful calibration of the methods used in a
quantitative analysis. These aspects of chemical analysis are a major preoccupation of the analyst.
THE FUNCTION OF ANALYTICAL CHEMISTRY


Chemical analysis is an indispensable servant of modern technology whilst
it partly depends on that modern technology for its operation. The two have


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INTRODUCTION

3

in fact developed hand in hand. From the earliest days of quantitative
chemistry in the latter part of the eighteenth century, chemical analysis has
provided an important basis for chemical development. For example, the
combustion studies of La Voisier and the atomic theory proposed by Dalton
had their bases in quantitative analytical evidence. The transistor provides a
more recent example of an invention which would have been almost
impossible to develop without sensitive and accurate chemical analysis. This
example is particularly interesting as it illustrates the synergic development
that is so frequently observed in differing fields. Having underpinned the
development of the transistor, analytical instrumentation now makes
extremely wide use of it. In modern technology, it is impossible to overestimate the importance of analysis. Some of the major areas of application
are listed below.
(a) Fundamental Research
The first steps in unravelling the details of an unknown system frequently
involve the identification of its constituents by qualitative chemical analysis.
Follow up investigations usually require structural information and quantitative measurements. This pattern appears in such diverse areas as the formulation of new drugs, the examination of meteorites, and studies on the results
of heavy ion bombardment by nuclear physicists.
(b) Product Development
The design and development of a new product will often depend upon

establishing a link between its chemical composition and its physical
properties or performance. Typical examples are the development of alloys
and of polymer composites.
(c) Product Quality Control

Most manufacturing industries require a uniform product quality. To ensure
that this requirement is met, both raw materials and finished products are
subjected to extensive chemical analysis. On the one hand, the necessary
constituents must be kept at the optimum levels, while on the other impurities
such as poisons in foodstuffs must be kept below the maximum allowed by law.
(d) Monitoring and Control of Pollutants

Residual heavy metals and organo-chlorine pesticides represent two well
known pollution problems. Sensitive and accurate analysis is required to
enable the distribution and level of a pollutant in the environment to be
assessed and routine chemical analysis is important in the control of industrial
effluents.


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4

ANALYTICAL CHEMISTRY

(e) Assay
In commercial dealings with raw materials such as ores, the value of the ore
is set by its metal content. Large amounts of material are often involved, so
that taken overall small differences in concentration can be of considerable
commercial significance. Accurate and reliable chemical analysis is thus

essential.

(f) Medical and Clinical Studies
The level of various elements and compounds in body fluids are important
indicators of physiological disorders. A high sugar content in urine indicating
a diabetic condition and lead in blood are probably the most well-known
examples.
ANALYTICAL PROBLEMS AND THEIR SOLUTION

The solutions of all analytical problems, both qualitative and quantitative,
follow the same basic pattern. This may be described under seven general
headings.

(1) Choice of Method
The selection of the method of analysis is a vital step in the solution of an
analytical problem. A choice cannot be made until the overall problem is
defined, and where possible a decision should be taken by the client and the
analyst in consultation. Inevitably, in the method selected, a compromise has
to be reached between the sensitivity, precision and accuracy desired of the
results and the costs involved. For example, X-ray fluorescence spectrometry
may provide rapid but rather imprecise quantitative results in a trace element
problem. Atomic absorption spectrophotometry, on the other hand, will
supply more precise data, but at the expense of more time consuming
chemical manipulations.

(2) Sampling
Correct sampling is the cornerstone of reliable analysis. The analyst must
decide in conjunction with his technological colleagues how, where, and when
a sample should be taken so as to be truly representative ofthe parameter that
is to be measured.


(3) Preliminary Sample Treatment
For quantitative analysis, the amount of sample taken is usually measured by
mass or volume. Where a homogeneous sample already exists, it may be
subdivided without further treatment. With many solids such as ores, however, crushing and mixing are a prior requirement. The sample often needs
additional preparation for analysis, such as drying, ignition and dissolution.


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INTRODUCTION

5

(4) Separations
A large proportion of analytical measurements is subject to interference from
other constituents of the sample. Newer methods increasingly employ instrumental techniques to distinguish between analyte and interference signals.
However, such distinction is not always possible and sometimes a selective
chemical reaction can be used to mask the interference. If this approach fails,
the separation of the analyte from the interfering component will become
necessary. Where quantitative measurements are to be made, separations
must also be quantitative or give a known recovery of the analyte.
(5) Final Measurement
This step is often the quickest and easiest of the seven but can only be as
reliable as the preceding stages. The fundamental necessity is a known
proportionality between the magnitude of the measurement and the amount
of analyte present. A wide variety of parameters may be measured (table 1.1).
(6) Method Validation
It is pointless carrying out the analysis unless the results obtained are known
to be meaningful. This can only be ensured by proper validation of the

method before use and subsequent monitoring of its performance. The
analysis of validated standards is the most satisfactory approach. Validated
standards have been extensively analysed by a variety of methods, and an
accepted value for the appropriate analyte obtained. A standard should be
selected with a matrix similar to that of the sample. In order to ensure
continued accurate analysis, standards must be re-analysed at regular
intervals.
(7) The Assessment of Results

Results obtained from an analysis must be assessed by the appropriate
statistical methods and their meaning considered in the light of the original
problem.
THE NATURE OF ANALYTICAL METHODS

It is common to find analytical methods classified as classical or instrumental,
the former comprising 'wet chemical' methods such as gravimetry and
titrimetry. Such a classification is historically derived and largely artificial
as there is no fundamental difference between the methods in the two groups.
All involve the correlation of a physical measurement with the analyte concentration. Indeed, very few analytical methods are entirely instrumental, and
most involve chemical manipulations prior to the instrumental measurement.


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ANALYTICAL CHEMISTRY

Table 1.1 A general classification of important analytical techniques
GROUP


gravimetric
volumetric
spectrometric
electrochemical
radiochemical
mass spectrometric
chromatographic
thermal

PROPERTY MEASURED

weight of pure analyte or of a stoichiometric
compound containing it
volume of standard reagent solution reacting
with the analyte
intensity of electromagnetic radiation emitted
or absorbed by the analyte
electrical properties of analyte solutions
intensity of nuclear radiations emitted by the
analyte
abundance of molecular fragments derived
from the analyte
physico-chemical properties of individual
analytes after separation
physico-chemical properties of the sample as it
is heated and cooled

A more satisfactory general classification is achieved in terms of the physical
parameter that is measured (table 1.1).

TRENDS IN ANALYTICAL METHODS AND PROCEDURES

There is constant development and change in the techniques and methods of
analytical chemistry. Better instrument design and a fuller understanding
of the mechanics of analytical processes enable steady improvements to be
made in sensitivity, precision, and accuracy. These same changes contribute
to more economic analysis as they frequently lead to the elimination of timeconsuming separation steps. The ultimate development in this direction is a
non-destructive method, which not only saves time but leaves the sample
unchanged for further examination or processing.
The automation of analysis, sometimes with the aid of laboratory robots,
has become increasingly important. For example, it enables a series of bench
analyses to be carried out more rapidly and efficiently, and with better
precision, while in other cases continuous monitoring of an analyte in a
production process is possible. Two of the most important developments in
recent years have been the incorporation of microprocessor control into
analytical instruments and their interfacing with micro- and minicomputers.
The microprocessor h3S brought improved instrument control, performance
and, through the ability to monitor the condition of component parts, easier
routine maintenance. Operation by relatively inexperienced personnel can


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INTRODUCTION

7

be facilitated by simple interactive keypad dialogues including the storage
and re-call of standard methods, report generation and diagnostic testing of
the system. Microcomputers with sophisticated data handling and graphics

software packages have likewise made a considerable impact on the
collection, storage, processing, enhancement and interpretation of
analytical data. Laboratory Information and Management Systems (LIMS) ,
for the automatic logging of large numbers of samples, Chemometrics, which
involve computerized and often sophisticated statistical analysis of data, and
Expert Systems, which provide interactive computerized guidance and
assessments in the solving of analytical problems, have all become important
in optimizing chemical analysis and maximizing the information it provides.
Analytical problems continue to arise in new fonns. Demands for analysis
at 'long range' by instrument packages steadily increase. Space probes,
'borehole logging' and deep sea studies exemplify these requirements. In
other fields, such as environmental and clinical studies, there is increasing
recognition of the importance of the exact chemical fonn of an element in a
sample rather than the mere level of its presence. Two well-known examples
are the much greater toxicity of organo-Iead and organo-mercury compounds
compared with their inorganic counterparts. An identification and detennination of the element in a specific chemical fonn presents the analyst with some
of his more difficult problems.

GLOSSARY OF TERMS

The following list of definitions, though by no means exhaustive, will help
both in the study and practice of analytical chemistry.

Accuracy
The closeness of an experimental measurement or result to the true or
accepted value (p. 14).
Analyte
Constituent of the sample which is to be studied by quantitative measurements or identified qualitatively.
Assay
A highly accurate detennination, usually of a valuable constituent in a

material oflarge bulk, e.g. minerals and ores. Also used in the assessment
of the purity of a material, e.g. the physiologically active constituent of
a phannaceutical product.


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ANALYTICAL CHEMISTRY

Background
That proportion of a measurement which arises from sources other than
the analyte itself. Individual contributions from instrumental sources,
added reagents and the matrix can, if desired, be evaluated separately.

Blank
A measurement or observation in which the sample is replaced by a
simulated matrix, the conditions otherwise being identical to those
under which a sample would be analysed. Thus, the blank can be used
to correct for background effects and to take account of analyte other
than that present in the sample which may be introduced during the
analysis, e.g. from reagents.

Calibration
1. A procedure which enables the response of an instrument to be related
to the mass, volume or concentration of an analyte in a sample by first
measuring the response from a sample of known composition or from a
known amount of the analyte, i.e. a standard. Often, a series of standards
is used to prepare a calibration curve in which instrument response is

plotted as a function of mass, volume or concentration of the analyte
over a given range. If the plot is linear, a calibration/actor (related to the
slope of the curve) may be calculated. This facilitates the rapid computation of results without reference to the original curve.
2. Determination of the accuracy of graduation marks on volumetric
apparatus by weighing measured volumes of water, or determinations
of the accuracy of weights by comparison with weights whose value is
known with a high degree of accuracy.

Concentration
The amount of a substance present in a given mass or volume of another
substance. The abbreviations wjw, wjv and vjv are sometimes used to
indicate whether the concentration quoted is based on the weights or
volumes of the two substances. Concentration may be expressed in
several ways. These are shown in table 1.2.

Constituent
A component of a sample; it may be further classified as:
major
minor
trace
ultra-trace

>10%
0.01-10%
1-100 ppm (0.000 1 %-0.01 %)
<1 ppm


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INTRODUCTION

Table 1.2 Alternative methods of expressing concentration*
UNITS

NAME AND SYMBOL

moles of solute per dm 3
equivalents of solute per dm 3
milli-equivalents of solute per dm 3
grams of solute per dm 3
parts per million
milligrams of component per kg
milligrams of solute per dm 3
parts per billion
nanograms of component per kg
nanograms of solute per dm 3
parts per trillion
picograms of component per kg
picograms of solute per dm 3

moldm- 3 , M
normal, N
meqdm- 3
gdm- 3
ppm (]I)
mgkg- 1
mgdm- 3

ppb
ngkg- 1
ngdm- 3
ppt
pgkg- 1
pgdm- 3

parts per hundred
millimoles of solute per lOOcm 3
grams of solute per lOOcm 3
milligrams of solute per lOOcm 3
micrograms of solute per lOOcm 3
nanograms of solute per lOOcm 3

% (w/w, w/v, v/v)

micrograms of solute per cm 3
micrograms per gram
nanograms of solute per cm 3
nanograms per gram
picograms of solute per cm 3
picograms per gram

j1gcm- 3
j1gg-1
ngcm- 3
ngg- 1
pgcm- 3
pgg-l


mM%
g%
mg%
j1g%

ng%
==ppm
== ppb
== ppt

* The table includes most of the methods of expressing concentration that are in current use, although some are not consistent
with S.I.

Detection Limit
The smallest amount or concentration of an analyte that can be detected
by a given procedure and with a given degree of confidence (p. 27).
Determination
A quantitative measure of an analyte with an accuracy of considerably
better than 10% of the amount present.
Equivalent
That amount of a substance which, in a specified chemical reaction,


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10

ANALYTICAL CHEMISTRY

produces, reacts with or can be indirectly equated with one mole

(6.023 x 10 23 ) of hydrogen ions. This confusing term is obsolete but its
use is still to be found in some analytical laboratories.

Estimation
A semi-quantitative measure of the amount of an analyte present in a
sample, i.e. an approximate measurement having an accuracy no better
than about 10% of the amount present.
Interference
An effect which alters or obscures the behaviour of an allalyte in an
analytical procedure. It may arise from the sample itself, from contaminants or reagents introduced during the procedure or from the
instrumentation used for the measurements.
Internal Standard
A compound or element added to all calibration standards and samples
in a constant known amount. Sometimes a major constituent of the
samples to be analysed can be used for this purpose. Instead of preparing
a conventional calibration curve of instrument response as a function of
analyte mass, volume or concentration, a response ratio is computed for
each calibration standard and sample, i.e. the instrument response for the
analyte is divided by the corresponding response for the fixed amount of
added internal standard. Ideally, the latter will be the same for each pair
of measurements but variations in experimental conditions may alter the
responses of both analyte and internal standard. However, their ratio
should be unaffected and should therefore be a more reliable function of
the mass, volume or concentration of the analyte than its response alone.
The analyte in a sample is determined from its response ratio using the
calibration graph and should be independent of sample size.
Masking
Treatment of a sample with a reagent to prevent interference with the
response of the analyte by other constituents of the sample (p. 41).
Matrix

The remainder of the sample of which the analyte forms a part.

Method
The overall description of the instructions for a particular analysis.


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INTRODUCTION

Precision
The random or indeterminate error associated with a measurement or
result. Sometimes called the variability, it can be represented statistically
by the standard deviation or relative standard deviation (coefficient of
variation) (p. 15).

Primary Standard
A substance whose purity and stability are particularly well-established
and with which other standards may be compared.

Procedure
A description of the practical steps involved in an analysis.

Reagent
A chemical used to produce a specified reaction
analytical procedure.

ill


relation to an

Sample
A substance or portion of a substance about which analytical information
is required.

Sensitivity
1. The change in the response from an analyte relative to a small variation
in the amount being determined. The sensitivity is equal to the slope
of the calibration curve, being constant if the curve is linear.
2. The ability of a method to facilitate the detection or determination
of an analyte.

Validation of Methods
In order to ensure that results yielded by a method are as accurate as
possible, it is essential to validate the method by analysing standards
which have an accepted analyte content, and a matrix similar to that of
the sample. The accepted values for these validated standards are
obtained by extensive analysis, using a range of different methods.
Internationally accepted standards are available.

Standard
1. A pure substance which reacts in a quantitative and known
stoichiometric manner with the analyte or a reagent.
2. The pure analyte or a substance containing an accurately known
amount of it which is used to calibrate an instrument or to standardize
a reagent solution.



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ANALYTICAL CHEMISTRY

Standard Addition
A method of quantitative analysis whereby the response from an analyte
is measured before and after adding a known amount of that analyte to
the sample. The amount of analyte originally in the sample is determined
from a calibration curve or by simple proportion if the curve is linear.
The main advantage of the method is that all measurements of the analyte
are made in the same matrix which eliminates interference effects arising
Table 1.3 Physical quantities and units including S.1. and C.G.S.
5.1.

C.O.S.

PHYSICAL QUANTITY

length, I
mass, m
time, t
energy, E

UNIT

SYMBOL

UNIT


SYMBOL

metre
kilogram
second
joule

m
kg
s
J

centimetre
gram
second
erg
electron volt
calorie

em

thermodynamic temkelvin
perature, T
amount of substance, n mole
newton
force, F
cubic metre
volume, V
cubic

decimetre
ampere
electric current, lor i
electric potential
volt
difference, E
ohm
electric resistance, R
electric conductance, G siemens
quantity of electricity,
coulomb
Q
electric capacitance, C farad
frequency, v
hertz
wavenumber, a (ii)
wavelength, l

metre
millimetre
micrometre
nanometre

magnetic flux density, B tesla
disintegration rate
curie
becquere1
nuclear cross-sectional
area
barn


K

mol
N
m3
dm3

A
V

a
S

C
F

Hz
m
mm

pm

nm
T
Ci
Bq

b


kelvin
mole
dyne
cubic centimetre
litre
ampere
volt
ohm
mho
coulomb
farad
cycles per second
reciprocal
centimetre
centimetre
millimetre
micron
millimicron
Angstrom
gauss
curie
barn

g
s

eV
cal
K


mol

cm 3 (ml)
1

A
V

a
a-I
C
F

cps
cm- 1
cm

mm
II
mp

A

G
Ci
b


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INTRODUCTION

13

from differences in the overall composition of sample and standards
(p. 32, 108).

Standardization
Determination of the concentration of an analyte or reagent solution
from its reaction with a standard or primary standard.
Technique
The principle upon which a group of methods is based.

Physical quantities relevant to analytical measurements and the units and
symbols used to express them are given in table 1.3. Both S.I. and C.G.S. units
have been included because of current widespread use of the latter and for
ease of comparison with older literature. However, only the S.I. nomenclature
is now officially recognized and the use of the C.G.S. system should be
progressively discouraged.
Further Reading
SKOOG, D. A. and WEST, D. M., Fundamentals of Analytical Chemistry, 4th Ed., CBS
College Publishing, New York, 1982.