Computers in Analytical Chemistry

480 Pages·1983·7.709 MB·English

by  R. Belcher (Eds.)

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Computers
in Analytical Chemistry
by
PHILIP G. BARKER, FBCS, FRSC
Principal Lecturer in Computer Science,
Teesside Polytechnic
Sometime Lecturer in Computing,
University of Durham
Sometime SRC Research Fellow,
Department of Chemistry (Swansea),
University of Wales
PERGAMON PRESS
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FEDERAL REPUBLIC Pergamon Press GmbH, Hammerweg 6,
OF GERMANY D-6242 Kronberg-Taunus, Federal Republic of Germany
Copyright © 1983 Philip G. Barker
All Rights Reserved. No part of this publication may be
reproduced, stored in a retrieval system or transmitted in
any form or by any means: electronic, electrostatic,
magnetic tape, mechanical, photocopying, recording or
otherwise, without permission in writing from the
publishers.
First edition 1983
Reprinted 1984
Library of Congress Cataloging in Publication Data
Barker, Philip G.
Computers in analytical chemistry.
(Pergamon series in analytical chemistry ; v. 6)
Includes bibliographical references and indexes.
I. Chemistry, Analytic—Data processing. I. Title.
II. Series.
QD75.4.E4B37 1983 543'.0028'54 82-22276
British Library Cataloguing in Publication Data
Barker, Philip G.
Computers in analytical chemistry—(Pergamon
series in analytical chemistry; 6)
1. Chemistry, and analytical —Data processing
I. Title
543'.0028'5 QD75.4.E4
ISBN 0-08-024008-9
In order to make this volume available as economically and
as rapidly as possible the author's typescript has been
reproduced in its original form. This method unfortunately
has its typographical limitations but it is hoped that they in
no way distract the reader.
Printed in Great Britain by A. Wheaton & Co. Ltd., Exeter
To God
Science and Humanity
Organisation of the Book
Chemical analysis and analytical chemistry are domains of scientific
endeavour that are fundamental tSo many areas of applied science and
technology. Taken together these subjects form a mass of knowledge which
has its own structure and subdivisions, theories and folklore, experts,
practitioners and manufacturing technology. Analytical chemistry thus
covers an extremely complex web of human activity. During the last
century Society has experienced many changes in technology that have
affected everybody's way of life - particularly the scientist and the way
in which scientific chemical analysis is undertaken. Moreover, the last
ten to fifteen years has seen the rapid growth of computer technology.
This too is slowly having its impact on analytical chemistry in a variety
of ways ranging from large scale automation through to laboratory machines
1
that show some degree of''intelligence. It is the intention of this book
to cover some of the ways in which computers are used in analytical
chemistry - the latter term being interpreted in its widest sense. An
understanding or background of chemistry/analytical chemistry is assumed.
Because of the all-pervasive nature of the subject an attempt is made in
Chapter One to answer the question, 'What is Analytical Chemistry?. It
does this by looking at some application areas in which analysis forms a
fundamental part of the day to day activity of those involved in its
practice. For the purpose of illustration, some techniques of analysis
are described in considerable detail. Obviously, the space devoted to
this chapter does not enable it to be comprehensive. Hopefully, though,
it will at least be representative of what happens in a wide variety of
analytical chemistry laboratories - if not in academia, then, at least, in
the commercial and industrial worlds.
In Chapter Two the author tries to formulate the basic steps involved in
the analytical process. Various illustrations are used to describe how a
computer system might assist the analyst in the sometimes formidable task
of analysing an unknown material. Here, fact occasionally turns to fancy
when a description is given of some of the ways in which computers may be
used in the not too distant future. On this front, some of the important
applications include the use of industrial robots, the use of sophisti-
cated mathematical modelling and simulation techniques, the creation of
large data bases and the application of artificial intelligence concepts
to the design of computer programs known as 'expert systems'. This
chapter also describes the influences that recent developments in computer
input and output devices are having on the way in which the analyst is
able to record and display the results of his/her work.
Chapter Three is devoted to a cursory study of some of the instruments
that are currently being used by analysts throughout a wide variety of
laboratories. It pays particular attention to those instruments that for
one reason or another require the application of computer technology. As
early as 1964 Joshua Lederberger at Stanford University was probably one
of the first to pioneer the use of real-time computer systems within the
laboratory environment. Since this early work, which was devoted to mass
spectral analysis, many significant advances have taken place. Nowadays
there are five important application areas of computers within analytical
instrumentation: (1) data acquisition, (2) data processing and enhance-
ment, (3) storage and retrieval of data, (4) automatic interpretation of
results, and (5) control uses. After presenting a simple model for a
typical analytical instrument and outlining some of its important
vii
viii Organisation of the Book
properties this chapter discusses some of the applications of computers in
three of the most important analytical methods: gas chromatography,
infrared and mass spectrometry. Obviously, many of the general principles
outlined in the specific examples chosen apply to a much wider range of
instrumentation. The chapter concludes with a description of how smaller
analytical units such as GC, IR, MS can be linked together to form more
'sophisticated* instruments.
Any form of technical description of computers is delayed until Chapter
Four. Here a description of small computer systems (microprocessors and
microcomputers), medium sized computers (minicomputers) and large
computers (mainframes and super-computers) is presented. The chapter
introduces the concepts of computer hardware and software. The archi-
tecture of a simple integrated circuit (or 'chip') is discussed in the
context of its being the building block for larger systems. Examples of
minicomputer, mainframe and super-computer systems are also briefly
outlined.
Control applications are an important facet of the computer. Equally
important - perhaps, more so - is its ablility to store and retrieve
data. In Chapter Five, the concepts of data collection (or data
acquisition) are discussed. Theoretical considerations relevant to
sampling theory are outlined and techniques for storing analogue and
digital data are briefly described. A summary of the various types of
storage device, such as magnetic tape and disks, is also given in this
section.
The inter-connection of instruments - both to each other and to computer
hardware - is a major area of interest within all branches of analytical
chemistry. Consequently, Chapter Six is devoted to the topic of
interfacing. Although the main emphasis is on electrical interfacing,
other forms are briefly outlined. Various types of standard electrical
and electronic interfaces such as the IEEE-488, CAMAC and S-100 are
described. In addition, some of the problems associated with the design,
implementation and use of non-standard interfaces are mentioned.
In Chapter Seven, as a natural follow-on from interfacing, the author
turns his attention to the basic types of communication channel that are
necessary to enable instrument/computer inter-connection and the flow of
data between one device and another. Several different types of communi-
cation link are discussed - couriers, wired links, optical fibres,
infrared data links, microwaves and satellite systems. Fundamental to
present day data communication are the world*s telecommunication net-
works. Consequently, in view of its importance, this chapter contains a
brief section devoted to basic telecommunications; the basic principles
of communication networks are introduced in order to provide the necessary
background for a later chapter on computer networks. Because of the need
to ensure the privacy of data and information that is transmitted over the
available communication links, the chapter concludes with a short
discussion of data encryption.
Progress in electronics, computing and precision engineering have made
possible significant advances in automation. Chemistry, in particular
applied analytical chemistry, has been unable to avoid the onward march of
this new area of technology. Automatic analysis is now a rapidly growing
sector of chemical science. Because of its importance, Chapter Eight is
devoted to a study of the application of automation to various aspects of
laboratory analysis. Several approaches are considered including the use
Organisation of the Book ix
of in-house development teams and the purchase or lease of turnkey
packages. A brief overview of the future potential role of the analyst
within this area is then given.
Chapter Nine deals with various aspects of data processing. Most of the
activities that take place in the laboratory produce data in one form or
another. Before information can be derived from experimental or
analytical measurements, the raw data obtained in the laboratory (or on
site) has to be processed by methods that are appropriate to the investi-
gation concerned. Several different approaches to computerised data
processing are outlined. The chapter discusses both numeric and non-
numeric techniques as well as some of the more advanced applications such
as pattern recognition, modelling and optimisation.
The storage of experimental results and other important information in
computer based systems requires the design and implementation of appro-
priate storage mechanisms. Computer data bases are often used to provide
the required facilities. In view of their growing importance, Chapter Ten
is used to present an introduction to this topic.
Because of the existing large volume and continual high growth rate of
information that is of relevance to analytical science - both its
literature and scientific results - the need for computerised information
services is of vital importance. Such services provide a variety of
computer based (or generated) tools to enable the analytical scientist to
gain access to and, hence, make use of the valuable work of other
scientists. The wide range of tools are grouped together under the title
of 'information services' and are described in Chapter Eleven.
Many large companies have geographically dispersed laboratories,
processing plants and administrative centres. The sharing of data,
information and control is of vital importance, as is the general coordi-
nation of an organisation's activity. Because of the growing interest in
the use of distributed communication systems for achieving these goals the
final chapter of the book is devoted to a study of computer networks.
Various types of system are described: local area, national and inter-
national networks. The fundamental modes of operation of these systems
are outlined and likely future directions of development summarised.
CAC - A*
Acknowledgements
I would like to express my sincere thanks to Professor D. Betteridge for
suggesting that this work should be undertaken. I am also indebted to the
University of Durham and Teesside Polytechnic for providing many of the
resources that enabled much of the background research to be undertaken.
Mr. Peter Henn and the staff of Pergamon Press contributed invaluable help
and advice. To all those who have helped me with the preparation of this
book I am deeply grateful.
xi
1
What is Analysis?
INTRODUCTION
Chemistry is one of the oldest sciences known to Mankind. Introductory
text books on the subject often describe its domain as: the science of
the properties of elementary and compound substances and the nature of the
laws that describe how these combine together and react one with another.
Chemistry is thus concerned with a wide range of topics. It deals with
the everyday objects and events that take place around us and with the
more esoteric entities and happenings on distant planets, in flames, in
ionization chambers and within the human body. It is concerned with the
discovery and manufacture of new materials (food, fuel, plastics, clothes
- to mention just a few) and the safety of the environment in which we
live - land, sea, river and the atmosphere. Above all it is a well
documented, progressive science that offers an exciting intellectual
framework for those wishing to embark upon its more detailed study.
For a variety of reasons, most people at some stage in their lives become
acquainted with the subject or with one or other of its multifarious
applications. Children often encounter the subject for the first time at
school - as one of the many options contained in an over-laden science
curriculum. Others gain their knowledge as a result of some less formal
interest - assaying the alcohol content of a wine they have been
fermenting; trying to ascertain why the soil in their garden will not
sustain the growth of roses; or, by means of a suitable dye, attempting to
restore the colour of a garment whose attractiveness has faded with old
age. Once kindled, an interest in chemistry is often difficult to
extinguish. Consequently, for a large number of people chemistry becomes
a professional discipline that forms the basis of a life long career.
Those who undertake a deeper, more involved, study of the subject do so as
a consequence of several possible factors. Some are motivated by the
financial rewards of their employment as professional chemists. Many
others are endowed with an insatiable desire to discover new knowledge and
cherish the accolades that this can bring. However, there are also those
who have a less professional interest and who treat the subject as a hobby
- just like stamp collecting, bird watching or painting. These are the
1
2 Computers in Analytical Chemistry
amateur chemists, of whom there are a great number. No matter how their
fundamental motivations may differ, those who pursue the discipline of
chemistry have much in common. This common ground undoubtedly embraces:
(a) an understanding of the basic principles of science and its
application to the bringing together of cause and effect; (b) some
knowledge of engineering principles and a desire to build things - the
chemist often constructs molecules, theories, experimental rigs and
measuring apparatus; and, (c) a working knowledge of the basic ideas
inherent in design - of synthetic pathways, of equipment and of analytical
techniques. Like other scientists, perhaps, the most fundamental
attribute that chemists have in common is that of being an observer. In
this context the feature that distinguishes the chemist from other
scientists lies in the nature of the systems that are dealt with and the
types of observations that are made.
Fundamental to chemistry - indeed, to all branches of science - are the
basic principles involved in the 'analytical method* (Ber68). Using this
approach a scientist sets about enumerating those factors which influence
a particular situation or state of affairs. An attempt is then made to
measure in a quantitative way the influences of the forces or factors that
are deemed to be important within the confines of the system that has been
chosen for investigation. All scientists are thus primarily concerned
with observations made on some particular, carefully selected, system.
Because of its subsequent importance, the concept of a system needs to be
more firmly established. In the broadest possible sense such an entity
may be defined as:
a set of objects together with relationships between
the objects and between their attributes (Wei75)
For the chemist, the objects of interest will be atoms and molecules. The
relationships will be the numerous laws that define how these entities
interact and react together. The attributes will be the various
properties that the atoms and molecules themselves possess. Such was the
definition of chemistry that might have been promoted years ago. Today
t
however, it is much more than this. Nowadays the definition of chemistry
and the scope of chemical systems must include the very process of life
and the mechanisms of living. The relationships mentioned above must be
extended to include a study of the ways in which atoms and molecules (and
their properties) affect people and other living species - if only roses
in an undernourished garden.
Provided one accepts the importance of gaining a knowledge of the
relationships and attributes that dominate a chemical system one must also
accept the need for appropriate methods to enable these to be elucidated
and recorded. Most often these objectives are realised through
1
controlled' experiments that incorporate proven measuring techniques that
form the basis of the scientist's interest in analytical chemistry.
However, despite the longevity of chemistry itself, it is only in
relatively recent times that chemical analysis has gained the hallmarks of
a precise and sophisticated science. Indeed, fewer than 100 years ago its
deficiencies were a cause for public scandal (Cam79).
As time progresses new measuring tools become available which are capable
of providing the scientist with previously unknown measuring capabilities.