Table Of ContentJOURNAL OF CHROMATOGRAPHY LIBRARY- volume 46
ion chromatography
principles and applications
Paul R. Haddad and Peter E. Jackson
Department of Analytical Chemistry, University of New South Wales,
P.O. Box 7, Kensington, N.S. W. 2033, Australia
ELSEVIER - - - - -
Amsterdam Boston Heidelberg London New York Oxford
- - - - -
Paris San Diego San Francisco Singapore Sydney Tokyo
ELSEVIER SCIENCE B.V.
Sara Burgcrliartstraat25
P.O.B ox 2 I I, loOn AE Arnstcrdam, Thc Ncthcrlands
C 1990 Elscvicr Scicncc B.V. All rights racwcd.
This work is protcctcd undcr copyright by Elscvicr Scicncc. and thc following tcm and conditions apply to its USC:
Photocopying
Single photocopies of single chapters may be made for personal use ns allowed by national copyright laws. Pcrmission
of thc Publishcr and paynmt of a fcc is quircd for all othcr photocopying. including multiplc or systcmaticc opying,
copying for advertising or promotional pwposcs. rcsalc. and all f i so fdocumcnt clclivcry. Special tatcs arc available
for educational institutions that wish to make pliutocopiw for lion-profit cducational classroom use.
Pcrmissions may bc sought dircctly fiorn Elscvicr's Scicncc & Technology RighLs Dcparhncnt in Oxford, UK: phone:
(+44)I X65 X43830, fax: (+44)I X65 853333, c-mil: pclrmissions(u~clscvicr.cum.Y ou may also wmplctc your qucst
on-line via the Elsevicr Sciencc Iiomepage (Iittp:l/wuw.elsevier.com), by selecting 'Customer Support' and then
'Obtaining Permissions'.
In tlic USA, USCIS m yc lear pcrmissions and make paymcnts through the Copyright Clcarancc Ccntcr, Inc., 222
Rosewood Drive. Danvers. MA 01923. USA: phone: ( t I) (978) 7508400. fax: ( I) (978) 7504744. and in the UK
through thc Copyright Liccnsing Agcncy Rapid Clcarancc Scrvicc (CLARCS), 90 Tottcnham Court Road, London
w1 P 0LP. UK;p honc: (+#) 207 631 5555; fa..: (+44) 207 63 I 55OCJ. Othcr CWnhia myh dVC a lWal rCprobTdphic
rights agency for payments.
Dcrivatiw Works
Tables of contents may bc reproduced for internal circulation, but pcrmission of Elscvicr Scicncc is required for
external resale or distribution of such material.
Pcrmission of thc Publishcr is rcquircd for all othcr dcrivativc works, including compilations and translations.
Electronic Storagc or Uwgc
Permission of thc Publishcr is rcquircd to storc or usc clcctronicallya ny matcrial containcd in this work, including any
cliaptcr or part of a chapter.
Except as outlined above, no part of this work myb e reproduced, stored in a retrieval system or transmitted in any
form or by any nlcans. dcctronic. mcchanical. photocopying. recording or othcnvisc. without prior writtcn pcrniission
of thc Publishcr.
Addrcss permissions rcqucsts to: Elscvicr's Scicncc & Tcchnology Rights Dcpartmcnt, at thc phonc. fax and c-mail
addrcsscs notcd abovc.
Notice
No responsibility is assiimed by the Publisher for any injury and/or damage to persons or property as a matter of
products liability. ncgligcncc or othcrwix. or from any usc or opcration of any mcthods, products. instructionso r idas
contiiincd in thc matcrial herein. Bccilusc of rapid advanccs in thc mcdical scicnccs, in particular, indcpcndcnt
vcrification of diagnoses and drug dosagcs should bc made.
Library of Congrm.8 Clt8loqing-in-Publication Data
Hadda.3, Paul P.
I m chroma:,yraphy : principlco and applications I Paul R. Haddad
and Filter E. Jackson.
p. crn. -- IJc-urnal of chromarography library ; v. 46)
111 .lucfes t.ibliuqx+~.hic.dl reterencer. Iriclu3cu iridex.
Tfl?}! 0-444-8873?-6
1. Ion nxchangc chr.mnatcqraphy. I. Jackson, Pctcr E. 11. Title.
111. Series.
91873. :4531133 133'2 90- 3 60 0 1
543' .OEg3--,jc:o CIP
First cditioti I990
Second imprcssion 1994
Third imprcssion 2003
ISBN: 0444-8x2324
@. The pap- uscd in this publication mccts thc rcquircmcnts of ANSlMlSO 239.48-1992 (Pcrmancncc of Pap).
Printed in TIic Netherlands.
vii
Preface
Ion chromatography (IC) was first introduced in 1975 and since that time, the
technique has grown in usage at a phenomenal rate. The reasons for this are clear; IC
offers the only simple, reliable and inexpensive means for the simultaneous separation
and determination of inorganic (and organic) ions in complex mixtures. The growth of
IC has been accompanied by a blumng of the original definition of the technique, so that
it now embraces a very wide range of separation and detection methods, many of which
bear little resemblance to the initial concept of ion-exchange separation coupled with
conductivity detection. We have chosen to define IC to encompass those modem column
liquid chromatographic methods which can be used for the determination of inorganic
anions and cations, water-soluble organic acids and bases, and ionic organometallic
compounds.
Using this definition, the separation methods which are applicable to IC include
ion-exchange chromatography, ion-interaction chromatography, ion-exclusion chromat-
ography, and some further, miscellaneous techniques. Appropriate detection methods
include conductivity, amperometry, coulometry, polarography, potentiometry,
spectrophotometry, atomic spectroscopy, refractive index measurements, luminescence
techniques and post-column reactions. This text is structured into five logical parts, each
of which groups chapters on related topics. Accordingly, Part I (Chapters 2-5) discusses
ion-exchange separation methods, whilst Part I1 (Chapters 6-8) treats the remainder of
the separation methods listed above. Part 111 (Chapters 9-13) is devoted solely to
detection methods, and Part IV (Chapters 14,15) concerns some practical aspects of IC.
Part V (Chapters 16-22) comprises a detailed, structured listing of experimental
conditions for the numerous applications of IC. The applications section is a unique
feature of this book and we hope it will become a valuable reference source for
practitioners of the technique. Throughout the book, we have attempted to integrate
suppressed and non-suppressed IC methods in the discussion of each aspect: that is, we
have emphasized the similarities between these two approaches, rather than their
differences.
In writing this book, we have endeavoured to provide a mly comprehensive text
which treats the principles and applications of IC and is suitable as a reference work for
both researchers and those involved with the use of IC in practical situations. Every
effort has been made to ensure that the literature coverage is as complete as possible for
the period 1975 to the early part of 1989, but we have also included some references
which are more recent than this. Throughout the text, each topic is discussed both from
a descriptive standpoint, in order to illustrate the underlying principles, and also from a
theoretical standpoint, in which a full mathematical treatment is provided. Theoretical
aspects, such as retention models and detector response equations, are presented either as
separate chapters or as clearly identified Sections. In this way, the theory can be
examined in depth or bypassed, according to the interests of the reader. The text has
been amplified by liberal usage of chromatograms and Tables showing practical
examples of each of the principles of IC, as they are discussed. We hope that this
viii
approach assists in the understanding of each point. Schematic overviews are also used
extensively so that the organization of each topic is clear. Abbreviations and acronyms
have been kept to a minimum and those that have been used are collected for ease of
reference in Appendix R, together with all of the symbols employed in the book. Special
attention has been given to the compilation of a comprehensive, detailed and cross-
referenced Index.
Writing a book of this size is an arduous task which cannot be accomplished by the
authors alone. We are greatly indebted to our many friends and colleagues who
provided assistance along the way and we would like to thank them sincerely for their
time and effort. Martin Dudman used his impeccable drafting skills to produce all of the
chromatograms and Helen Shumsky performed all of the photographic work required
for preparation of the Figurcs. The staff of the Physical Sciences Library of the
University of New South Wales, and of the Technical Library at Millipore Waters,
cheerfully procured hundreds of journal articles. Only through their capable efforts
have we been able to achieve a comprehensive coverage of the literature. Numerous
colleagues, both within Australia and overseas, provided valuable and enlightened
comments on the manuscript, or helped with proof reading. In this regard, thanks are
due especially to Jim Fritz and Petr Jandik, and to the following students in the IC
research group at the University of New South Wales; Roy Foley, Chris Cowie, John
Brayan, Andrew Sosirnenko and Peter Fagan. We gratefully acknowledge those
publishers and authors who have granted permission for us to reproduce Figures from
their publications.
Finally, this book would never have been completed without the support,
encouragement and love of the members of the fladdad family; Simone made the coffee,
Lianne filed the reprints, Christopher shared his bedroom with a computer and Kerry's
patience and acceptance kept everything and everyone together over two years with a
part-time husband and father.
Paul R. Haddnd,
Peter E. Jackson
Kensington, I990
Technical nofe: Text and artwork (with the exception of chromatograms) for this book were
produced on an Apple Macintosh@ IIcx microcomputer, using Microsoft@ Word 4.0 (Microsoft
Corporation), McDraw (Apple@ Computer Inc.), Cricket Graph (Cricket Software) and
MathWriteP (Cooke Publications) software packages, and was printed in camera-ready form on an
Apple Laserwrite@.
1
Chapter 1
Introduction
1.1 BACKGROUND TO ION CHROMATOGRAPHY
Ion chromatography (abbreviated throughout this text as IC) is an analytical
technique for the separation and determination of ionic solutes. A more detailed
definition is presented later in Section 1.3. IC falls into the general classification of
liquid-solid chromatographic methods, in which a liquid (called the eluent) is passed
through a solid stationary phase and then to a flow-through detector. The stationary
phase is usually in the form of small-diameter (e.g. 5 pm), uniform particles which are
packed into a cylindrical column. This column is constructed from a rigid material
(such as stainless steel or plastic) and is generally 5-30 cm long, with an internal
diameter in the range 4-9 mm. The stationary phase particles are packed uniformly into
the column and are retained by means of porous frits located at each end of the column.
A high-pressure pump is required to force the eluent through the column at typical flow-
rates of 1-2 ml/min. The sample to be separated is introduced into the flowing eluent
stream by means of an injection device inserted into the flow-path prior to the column.
The detector usually contains a low volume (e.g. 4 pl) cell through which the eluent
flows. The components of an ion chromatograph are shown schematically in Fig. 1.1.
The ion chromatograph is operated in the elution mode. That is, a discrete amount
of the sample is applied to the top of the column (via the injector), whilst the eluent is
passed continuously through the column. The sample components progress through the
column at different rates and therefore enter the detector at different times. The
detector senses the sample components and produces the chromatogram. This process is
illustrated schematically in Fig. 1.2.
Sample
Eluent delivery injection Separation Detection
Fig. 1.1 Components of an ion chromatograph.
2 Chapter 1
Sample Eluent
A+B
A
B
Time
Fig. 1.2 Schematic illustration of the separation of two components (A and B) by IC.
1.1.1 Hardware and software components
Any chromatographic system of the type shown in Fig. 1.1 can be divided into
hardware and software components. The hardware comprises the instrumentation
(pump, injector, detector and data station), whereas the software consists of the variable
components of the system (principally the nature of the stationary phase, the composition
of the eluent and the flow-rate). This book concentrates on the software of IC.
Hardware components will not be discussed, since these components are derived from
(and in many cases are identical to) instrumentation developed for High Performance
Liquid Chromatography (HPLC). The construction and operation of HPLC equipment
has been treated thoroughly elsewhere 1e.g. 11. We need only note that a typical IC
instrument uses a loop injector, a dual reciprocating piston pump (often with pulse
dampeners to reduce pressure pulsations) and a chart recorder or computing integrator.
The nature of the detector used is variable, but conductivity detectors are employed most
frequently. We can further note that the hardware components in contact with the eluent
can be constructed from either a polymeric material (e.g. PTFE) or stainless steel. The
former material may be preferable when trace metal determinations are to be
performed, since there is some possibility of contamination of the sample and eluent by
metal ions produced from corrosion of stainless steel.
1.1.2 The chromatographic separation process
When a sample is introduced into an IC system, an equilibrium is established for
each sample component between the eluent and stationary phases. Thus, for a component
A we can write:
Introduction 3
Fig. 1.3 Schematic illustration of the distribution of solute molecules (represented by the black
dots) between the stationary and mobile phases when the distribution coefficient DA is (a) low and
(b) high.
Am % A,
where the subscript m refers to the mobile (eluent) phase and r refers to the stationary
phase. The distribution of component A between the two phases is given by the
distribution coefficient, DA,w here:
The value of DA is dependent on the size of the population of molecules of
component A in the stationary and eluent phases. This is represented schematically in
Fig. 1.3, which shows the distribution of component A between the stationary and eluent
phases for a small (Fig. 1.3(a)) and a large (Fig. 1.3(b)) value of DA. Since the
equilibrium shown in eqn. (1.1) is dynamic, there is a continual, rapid interchange of
molecules of component A between the two phases. The fraction of time, fm, that an
average molecule of A spends in the mobile phase is given by:
amount of A in mobile phase
fm= (1.3)
total amount of A
That is,
(1.4)
(1.5)
where Vm is the volume of the mobile phase and w is the weight of stationary phase (this
4 Chapter I
latter parameter is more convenient, but perhaps less logical, to use than the volume of
the stationary phase). If we now define a new variable called the cupucityfuctor, k', as:
k' = DA($) (1.6)
then eqn. (1.5) can be rewritten as:
-1
f, = (1.7)
1 +k'
Now the rate of travel of component A through the chromatographic system can be
obtained by multiplying fm by the average linear velocity of the mobile phase, u, to give:
L)
-
Rate of travel of A = u (1 (1.8)
The rate of travel will therefore be determined by the average velocity of the
mobile phase, the volume of mobile phase, the weight of stationary phase and the
distribution coefficient for the particular component. If the chromatographic
parameters remain constant, the only factor which changes from one sample component
to the next is the distribution ratio. Provided that each component has a unique value of
the distribution ratio, then each component will have a different (and characteristic) rate
of travel through the stationary phase. That is, each component will emerge from the
column at a characteristic retention time.
1.1.3 The chromatogram
A representative chromatogram for two sample components is shown in Fig. 1.4.
This chromatogram shows three peaks; one for each sample component (A and B) and a
so-called "solvent" or "injection" peak. The first of these peaks contains the solvent in
which the sample is dissolved, together with those components of the sample which show
no interaction with the stationary phase. The sample solvent and unretained components
take some time to pass through the column and interconnecting tubing, even though they
do not interact with the stationary phase. This time is designated as the void time, to.
Similarly, the time at which each retained solute appears is known as the retention time,
tR, for that component.
The values of to and tR will depend on the flow-rate of the mobile phase and the
physical dimensions of the column and connecting tubing. It is therefore often
convenient to express the retention of a component in terms of its capacity factor, which
is expressed as:
(1.9)
Introduction 5
Solvent
-
lime
Fig 1.4 A typical ion chromatogram resulting when a mixture of two sample components (1 and
2) is injected.
1.1.4 Mechanisms of interaction
Up to this stage, we have not specified the manner in which the sample components
interact with the stationary and mobile phases. The actual mechanism by which this
interaction occurs is one simple means for classifying chromatographic methods into
broad groups. For example, the sample components may be retained on the stationary
phase through the interaction of permanent dipoles on the component with permanent
dipoles on the stationary phase. This results in an adsorption mechanism and gives rise
to the general class of adsorption chromatographic methods in which polar stationary
phases are employed. Similarly, partition chromatographic methods may be classified as
those which involve the distribution of sample components between two immiscible fluid
phases, one of which is immobilized to form the stationary phase. Subdivision of these
general classes can then be made. according to the physical states of the stationary and
mobile phases. For example, gas-liquid chromatography uses a gaseous mobile phase
and a liquid stationary phase; liquid-solid chromatography (which embraces IC) uses a
liquid mobile phase and a,solid stationary phase.
It is unfortunate that IC does not lend itself readily to such a simple definition,
because a wide range of different interaction mechanisms is employed. In the following
Section, we will provide a working definition of IC which will be used to define the
scope of this book.
6 Chapter 1
1.2 WHAT IS ION CHROMATOGRAPHY?
1.2.1 Historical aspects
The foundations for modem IC were laid down by Small, Stevens and Bauman in
1975, when they described a novel ion-exchange chromatographic method for the
separation and conductimetric detection of anionic and cationic species [2]. Their
method employed a low-capacity ion-exchange stationary phase for the separation step,
together with a second column and conductivity detector which comprised the detection
system for continuous monitoring of the eluted ions. The second column was called a
"stripper" column (which was later called a "suppressor") and this column served to
reduce the background conductance of the eluent in order to enhance the detectability
of the eluted ions. The term "Ion Chromatography" was introduced only when this
technology was licensed to the Dionex Corporation for commercial development. For
this reason. IC was originally interpreted to mean the specific use of the same
combination of separation and detection modes as reported in the original publication.
The growth of IC was very rapid because it provided, for the first time, a reliable and
accurate method for the simultaneous determination of many simple inorganic anions and
cations. In the early stages of its development, IC was seen essentially as a tool for
inorganic analysis, but this perception changed with the realization that many organic
solutes could also be analyzed using the same approach. This, in turn, led to the use of
different stationary phases and detectors, so the original definition of IC became
somewhat inaccurate. Later developments in 1979 by Gjerde, Fritz and Schmuckler [3-51
showed that the stripper column was not essential to successful conductivity detection,
provided the correct types of stationary phase and eluent were used. At about the same
time, the separation of inorganic ions on traditional c18 reversed-phase columns was
demonstrated [e.g. 61. Although not specifically suggested by the authors of these
papers, the new methods became commonly referred to as IC.
1.2.2 Definition
We are therefore left with the situation where the technique of 1C is very loosely
defined, both in terms of the manner in which the solutes are separated and the types of
solutes applicable to the technique. For this reason, it is pertinent to begin this book by
delineating the range of techniques and applications which are to be included in our
working definition of IC. We will consider IC to encompass those column liquid
chromatographic techniques which can be used for the determination of
(i) Inorganic anions, such as Cl-, Br, Sod2-,e fc.
(ii) Inorganic cations, including alkali metal, alkaline earth, transition metal and
rare earth ions, but not including neutral metal chelates.
(iii) Low molecular weight (water soluble) carboxylic acids, such as formic acid,
acetic acid, etc., and organic sulfonic acids, including detergents.
(iv) Low molecular weight (water soluble) organic bases.
(v) Ionic organometallic compounds, such as tributyltin, etc-.
