Basic chemometric techniques in atomic spectroscopy

430 Pages·2013·6.438 MB·English

Basic Chemometric Techniques in Atomic Spectroscopy
2nd Edition
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RSC Analytical Spectroscopy Monographs
Series Editor:
Neil W. Barnett, Deakin University, Victoria, Australia
01 Advisory Board:
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FP F. Adams, Universitaire Instelling Antwerp, Wirijk, Belgium; M.J. Adams,
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4 RMIT University, Melbourne, Australia; R.F. Browner, Georgia Institute of
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3 Technology, Atlanta, Georgia, USA; J.M. Chalmers, VSConsulting, Stokesley,
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4 UK; B. Chase, DuPont Central Research, Wilmington, Delaware, USA;
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8 M.S. Cresser, University of York, UK; J. Monaghan, University of Edinburgh,
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9/ UK; A. Sanz Medel, Universidad de Oviedo, Spain; R.D. Snook, UMIST, UK
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1 Titles in the Series:
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d 1: Flame Spectrometry in Environmental Chemical Analysis: A Practical
org | Guide
sc. 2: Chemometrics in Analytical Spectroscopy
bs.r 3: Inductively Coupled and Microwave Induced Plasma Sources for Mass
u
p://p Spectrometry
htt 4: Industrial Analysis with Vibrational Spectroscopy
on 5: Ionization Methods in Organic Mass Spectrometry
aded e 2013 67:: QGuloawntDitaisticvhearMgeillOimpetitcraelWEmaviessleionngtShpSepctercotrsocompeyt:ryA Practical Guide
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wnl7 Ju 8: Chemometrics in Analytical Spectroscopy, 2nd Edition
Don 1 9: Raman Spectroscopy in Archaeology and Art History
d o 10: Basic Chemometric Techniques in Atomic Spectroscopy
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h 11: Biomedical Applications of Synchrotron Infrared Microspectroscopy
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13: Basic Chemometric Techniques in Atomic Spectroscopy, 2nd Edition
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Basic Chemometric Techniques in
Atomic Spectroscopy
nd
2 Edition
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93 Edited by
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1 Jose´ M. Andrade-Garda
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u RSCAnalyticalSpectroscopyMonographsNo.13
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F Preface
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1 This book is rooted on an informal discussion with three researchers, Dr
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oi:1 Alatzne Carlosena, Dr Mo´nica Felipe and Dr Marı´a Jesu´s Cal, after they had
g | d some trouble measuring antimony in soils and sediments using electrothermal
or atomic absorption spectrometry. While we reviewed the results and debated
c.
s possibleproblems,muchlikeinabrainstormingsession,Irealizedthatsomeof
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p:// [mid-infrared(IR)spectroscopy,whereIhadsomeexperience],namely,alack
htt of peak reproducibility, noise, uncontrollable amounts of concomitants,
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aded e 2013 troAscsopmyaunsyinogfmthueltsievadriiaffitecurletgiersessairoencmuerrthenotdlys(oovremrcuolmtiveariinatemcohleecmuolamrestrpieccs)-
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wnl7 Ju Iproposed that these three ladiesshouldapplythem totheir spectra.The first
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this until they found a way to do it.
The number of papers we found that reported on the use of multivariate
regressioninatomicspectrometrywassmall,andweguessedthatthismightbe
because of eithera lack ofgeneral awareness of thehuge potential capabilities
of these techniques and/or the difficulties in extracting the spectral data from
the spectrometers, something that is trivial for most instruments dedicated to
molecular spectrometry.
Wegotsomegoodresults,andonemorningIreadane-mailfromDrMerlin
Fox(CommissioningEditorofTheRoyalSocietyofChemistry)withatotally
surprising proposal: to prepare a monograph on the subject. After reading his
e-mail several times and asking him if that was true (some electronic ‘spam’
seemed very possible), DrCarlosena and I contacted severalgood scientistsin
RSCAnalyticalSpectroscopyMonographsNo.13
BasicChemometricTechniquesinAtomicSpectroscopy:2ndEdition
EditedbyJose´ M.Andrade-Garda
rTheRoyalSocietyofChemistry2013
PublishedbytheRoyalSocietyofChemistry,www.rsc.org
v
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vi Preface
the two fields of atomic spectrometry and chemometrics. I am indebted to all
authors for their constructive words and immediate collaboration, although,
maybe, it was the first one we contacted, Prof. Alfredo Sanz-Medel (a
worldwide-reputed atomic spectroscopist, with several international awards,
including the 2007 Robert Kellner Lecture), who really fuelled us to go on.
05 Ireallywanttoexpressmydeepandsinceregratitudetoeachparticipantinthis
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P exciting project. You are not only skilful scientists but also nice persons,
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44- enthusiastic workers and, first of all, good friends. Recognition is also due to
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39 Merlin Fox for his continuous support and encouragement. His proposal for
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49 thesecondeditionofthisbookwas,simply,unexpectedandawonderfulnews.
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81 The main photographs on the cover are credited to a good friend, Sabino
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9/9 Muin˜o-Varela,andtheirfinalsetupisaresultoftheenormouspatienceofmy
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0 dear colleague, Alatzne.
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0. Finally,ourthankstoyou,thereader.Itisthehonestdesireoftheauthorsto
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oi: hear from you. We would like to receive your feedback. It is impossible to
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g | produce a text like this that satisfies everyone, their expectations and needs.
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c. Many things were left out of the book, but if you feel that some more expla-
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s.r nations,reviewsorinformationarerequired,please,donothesitatetocontact
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p:// greatly appreciated and, as far as possible, included in it (and publicly
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he cation is far from trivial. Dr Rosa Soto-Ferreiro and my undergraduate
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they discussed and ‘complained’, the more I learnt about the difficulties of the
technique.
Jose´ Manuel Andrade-Garda
A Corun˜a, Galicia, Spain
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F Structure of the Book
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1 It was very clear from the beginning that the main objective of this project
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oi:1 would be to present atomic spectroscopists with the basis of the most widely
g | d appliedmultivariateregressiontechniques.Wedidnotwantjust‘anotherbook
or on chemometrics’ and, instead, we challenged ourselves to present some
c.
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s.r
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htt some issues were tackled in one way rather than in another. We tried to keep
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wnl7 Ju sound background on chemometrics is highly advisable. Please, consider it as
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arepresentedtothereader.Practicaldifficultiesarereferredto, theirsolutions
depicted and, when possible, multivariate chemometric solutions pointed out.
The second chapter reviews univariate calibration. Although thismight seem
trivial for researchers it is observed too frequently, even in papers published in
prestigious journals, that fundamental issues have been overlooked and,
therefore, the results might be questionable. Chemists must be aware of some
fundamental problems caused by the way in which we use the regression line
obtainedusingthewell-known(?)least-squarescriterion.Ithappensthatwedo
not have an exact mathematical solution and, therefore, we are forced to use
approximations,whichareacceptableundersomerestrictedconditions.Further,
different equations are published in literature and their differences/similarities
not always explained. We have tried to present a unified approach. In this
RSCAnalyticalSpectroscopyMonographsNo.13
BasicChemometricTechniquesinAtomicSpectroscopy:2ndEdition
EditedbyJose´ M.Andrade-Garda
rTheRoyalSocietyofChemistry2013
PublishedbytheRoyalSocietyofChemistry,www.rsc.org
vii
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viii StructureoftheBook
chapterasmallamountofmathematicswasincludedbecausetheoverallmatter
soundsfamiliartomostusersandbecauseunivariateregressionisacriticaltool
inevery laboratory which deliversresults and evaluates theiruncertainty.
Chapter 3 deals with a critical statement that any analyst and chemomet-
rician hasto remember: no good chemometric analysiscan be obtained unless
07 theoriginaldataaretrustworthy.Oneofthekeyobjectivesofchemometricsis
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44- the data are correct. To obtain reliable data, we can use a suite of dedicated
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39 chemometric tools aimed at developing good analytical methodologies. Thus,
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49 experimentaldesign,optimizationandrobustnessarecornerstonestoassessing
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81 accuracy during any process of method development. Typical methodologies
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9/9 are introduced and discussed, along with extensive literature reviews that
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0 combine objective optimization and atomic spectrometry.
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0. Chapter 4 retrieves the basic ideas of classical univariate calibration as the
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oi: standpoint from which the natural and intuitive extension of multiple linear
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c. laboratorytasksand,therefore,theproblemsassociatedwithitsuseareexplained
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s.r insomedetail.Suchproblemsjustifytheuseofothermoreadvancedtechniques.
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p:// components analysis can tackle it is the next step forward. This constitutes the
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ownlo17 Jun Gmraathpehmicaatliceaxlplabnaactkigornosuonfdm. aSneyvecroanlcecpotmsmaroengivaepnp,raolaocnhgeswittohasomlvoerecfuorrrmenatl
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o problems are suggested, along with the golden rule that ‘there is not a golden
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he rule’. The development of a satisfactory regression model can alleviate the
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concentration, etc.), but only when a strict and serious job is performed with
the regression software. Iteration is the key word here, as the analyst has to
iterate within his/her data and within the software capabilities. Validation is a
keypointthatwillneverbestressedsufficientlyenough.Inthis2ndeditionwe
included a comprehensive approach to derive typical figures-of-merit from
multivariate models. This includes the new alternatives given by the Inter-
national Organization for Standardization (ISO) and the European Union to
the former ‘limit of detection’ and ‘limit of quantification’. Many discussions
herearebasedontheexcellentworkfromtheresearchgroupofProfessorsLuis
Sarabia and Marı´a Cruz Ortı´z (University of Burgos).
Finally, Chapter 6 goes into two new regression paradigms: artificial neural
networks and support vector machines. Quite different from the other
regressionmethodspresentedinthebook,theyaregainingacceptancebecause
they can handle non-linear systems and/or noisy data. This step forward
is introduced briefly and, once more, a review is presented with practical
applications in the atomic spectroscopy field. Not surprisingly, most
papers deal with complex measurements [e.g. non-linear calibration or
View Online
StructureoftheBook ix
concomitants-affected measurements in electrothermal atomic absorption
spectroscopy (ETAAS)] and/or new analytical atomic techniques [which,
therefore,yieldverycomplexdata;e.g.X-rayfluorescenceincomplexsystems,
laser-inducedbreakdownspectrometry(LIBS)andseveralsecondaryionmass
spectrometry (SIMS)-based methodologies].
07 Two distinctive features of this new edition are that more worked examples
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44- chapters dealing with multivariate calibration. It is the authors’ desire that
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39 thesewillhelpthereadertovisualizethedifferentmodelsthatcanbeobtained
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49 using different regression methods.
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