MASS SPECTROMETRY BASICS Christopher G. Herbert Aobert A.W. Johnstone CRC PRESS BocaRaton London NewYork Washington, D.C. Library ofCongress Cataloging-in-PublicationData Herbert, ChristopherG. Mass spectrometry basicsI Christopher G. Herbert, RobertA.W.Johnstone. p.; em. Compilation ofarticles previously published in theseriesBack-to-basics. Includes bibliographicalreferences andindex. ISBN0-8493-1354-6 (alk.paper) I. Mass spectrometry.1.Johnstone, R.A.W.(RobertAlexanderWalker)II.Title. [DNLM: 1.SpectrumAnalysis, Mass-CollectedWorks.2.SpectrumAnalysis, Mass--Handbooks. QC454.M3 H536m2002] QP519.9.M3 H47 2002 543'.0873-<lc21 2002025935 This book contains information obtained from authentic and highly regarded sources. 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Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identificationand explanation, without intenttoinfringe. Visit the CRC Press Web site at www.crcpress.com ©2003by CRePress LLC No claim tooriginalU.S. Governmentworks International StandardBook Number0-8493-1354-6 Library ofCongressCard Number2002025935 Printed in theUnited StatesofAmerica 2 3 4 5 6 7 8 9 0 Printed onacid-freepaper Dedication Dedicated to Christine, Steven, and Fiona RAWJ Pauline, Daniel, Joseph, and Emma CGH Preface This book began as a small series of brief articles designed to assist engineers and salesmen in understanding some aspects of ion chemistry and mass spectrometry. Each article was composed of a very short summary and a longer section that described aspects of the subject matter in somewhat greater detail. To facilitate rapid reading and assimilation, extensive use was made of figuresand tables, which contain additional information in their legends or footnotes. Fromthe outsetofwriting these articles, it was never intendedthat they should beexhaustively comprehensive, because this approach would have defeated the aims of the whole exercise, viz., the provision of short, quick explanations of major elements of mass spectrometry and closely alliedtopics. The traditional, more all-embracing approach to writing about mass spectrometry was leftto the many excellent authors, who have provided impressive textbooks. In contrast, the major objective of the Back-tv-Basics series was the provision of quick explanations of fundamental concepts in mass spectrometry, without overelaboration. As far as possible, descriptions of pro cesses, applications, and underlying science were made with a minimum of text backed up by easily and rapidly understood pictures. Although some major equations of relevance to mass spectrometry have been introduced, the mathematical derivations of these equations were largely omitted.This was not an attempt to dumb down an important discipline. Rather, the intent was to make some of the esoteric aspects of an important area of analysis readily comprehensible to the manypeople who have to deal with mass spectrometers but who have not been trained specifically in this branch of science and engineering. The series began about ten years ago and encompasses recent and past developments in mass spectrometry. However, since it is the principles of mass spectrometry that are explained and not specific instrumentation, the information contentremains as relevant now as it was ten years ago. The effort to clarify and articulate the principles of spectrometry as simply as possible appears to have struck a welcome response among those who use mass spectrometers. The original series was not advertised, but, once it had been discovered outside the Micromass organization, there were inquiries as to how it could be purchased. From the start, Micromass offered the series free in a ring-binder format and later also provided it free on CD ROM and then on the Internet. Updating of the first CD led to over 600 requests for it on the day after its releasehad beenannouncedon the Internet. Partly because ofthis response- but mainly because users or potential users frequently like to have a traditional reference book - it was decided to publish the series in this present book form. This preface would not becomplete withoutthe authors sincerely thanking anumberofpeople and,in particular, Micromass UiK. for its pastkeen support and for its permission to proceed with publishing this book. A successful business is composed of enthusiastic people, and it would be remiss of the authors not to thank all those many individuals in Micromass who have provided countless pieces of advice and help. Lastly, the authors wish to acknowledge with gratitude the supportofNorman Lynaugh, TonyHickson, and especiallyJohn Race for his original perspicacious decision to encourage the series to go ahead and for the ideas he proffered throughout. As he once run famously remarked, "There are a lot of poor souls out there who are being asked to mass spectrometers but who know next to nothing about mass spectrometry," At least we think it was "souls" he said! Chris Herbert Bob Johnstone The Authors Robert A.W.Johnstone, Ph.D., isafullprofessorin theDepartmentofChemistry at theUniversity ofLiverpool, Liverpool, Ll.K. He possesses a D.Sc., a Ph.D., and a B.Sc. in chemistry. He is also aFellowof The Royal Society of Chemistry (FRSC). An author and contributor to several books, Dr. Johnstone has published over 200 journal papers in natural product chemistry, catalysis in oxidation and reduction, and spectroscopy. His work has resulted in several new synthetic proce dures in organic chemistry that are widely used and have provided some 30 full patents. Part of his research with industry led to a Queen's Award for Technological Achievement, an award not usuallygiven to industrial and business enterprises and not normally given to university staff. The awardconcerned large-scale manufacture of an important ingredient of timber preservative by a newcatalytic method, whichproduces about 3000tper annum oftheproduct. Apart from his career inuniversities,heis alsoadirectorofthree consulting, biotechnological, and animationcompanies, andhe has worked for the Medical Research Council as a research scientist. Professor Johnstone has acted as visiting professor at a number of universities in Europe, China, and Australia. In his privatelife, Bob has a wife Christine and two children: Steve, a geological scientist in Australia; andFiona, a Director of Public Health in the National Health Service. He has played rugby and Association football, hockey, and badminton but now accepts more leisurely walking as his main physical exercise. As part of his interests in woodworking and metalwork, he has found time to acquirethe status of qualified plumber. Christopher G. Herbertis the Marketing Materials and Reprographics Manager with Micromass U.K.Ltd., Atlas Park, Simonsway, Manchester, U.K. He possesses a Higher National Diploma in applied physics and is a graduate of The Institute of Physics. He has over 32 years of experience workinginthefieldofmass spectrometry withMicromass U.K.Ltd.Hisearlierroles inthecompany includedevelopment engineer, testand installationengineer, test andinstallationmanager, technical author (instruction manuals), and webmaster. He is author and coauthor of several hundred publi cationson mass spectrometry and its applications. In his private life, Chris has a wife Pauline and threechildren: Daniel, a chartered engineer; Joseph, a research scientist at the Daresbury Labora tory;and Emma, a full-time mother. Chris has a team of racing pigeons competing in races up to 500 miles and is chairman and clock setter for his local pigeon-flying club. In an effort to prove heis asfast as his pigeons, Chris has three times completed the London marathon, twice with his wife,raising over £1000 for the British Heart Foundation and other charities. Introduction Back-tv-Basics Was not originally designed to be a book but, rather, a series ofarticles, each on a topic dealing directly or indirectly with an aspect of mass spectrometry. Each article in the series was intended to be a self-contained, brief (but not superficial) explanation of an area of mass spectrometric instrumentation or theory. The aim was to provide nonexperts with enough informa tion to understand the major fundamental concepts underlying any chosen topic. Because basic factswere being described, the title ofthe series became Back-tv-Basics. For example, one of the earliest articles covered the theory and uses of electron ionization in mass spectrometry. To ease understanding, a complex rigorous approach was forsaken in favor of a straightforward account, aided by many clear diagrams. By describing many of the basics of mass spectrometry and not individual instruments per se, the series was not subject to the obsolescence that typically afflicts books composed around a rapidly advancing subject area such as mass spectrometry. The basic articlescover principles, which largely do not change, and therefore the articles remain useful over longer periods oftime. Of course, fashions change in mass spectrometry as in anything else. For example,thermospray inlets for mass spectrometers have given way to more efficient ones, but the principles underlying a thermospray device are still valid and are worth retaining on record. Although each Back-to-Basics article is quite brief, a very short summary of each article is providedinAppendixA for readers who want a succinct, informative account that provides aquick working understanding of the topic. As the number ofarticles increased, many of them had to be cross-referenced to other entries inthe series. Therefore, although the series began as a few articles on isolated topics, as the series built up, the cross-referencing network increased as well. The collected articles were originally offeredinring-binder format but, as the numberofarticlesincreased, this format became unwieldy. Although the hardcopy versions of the Back-to-Basics series remained available to the hundreds ofregular subscribers, it was decidedto postthe series onthe Internetfor wideravailability. Finally, the articles were assembled in CD format and again made freely available by Micromass U.K. Theresult ofthe Back-tv-Basics series is an accumulation ofsome 50 separate but interrelated expositions ofmass spectrometricprinciples and apparatus. Some areas ofmass spectrometry, such as ion cyclotron resonance and ion trap instruments, have not been covered except for passing references. This decision has not been due to any bias by the authors or Micromass but simply reflects the large amount of writing that had to be done and the needs of the greatest proportion of users. For various reasons, it has been decided to close the present series of Back-to-Basics and collect the articles in a book that can be placed on a shelf and used as a reference source. It is an unusual book format, having a large number of rather short chapters together with a collection of brief summaries, included as Appendix A. Thus the book will still serve the dual purposes of describing fundamentals and additionally providing a concise synopsis ofeach article. In another departure from regular scientific book format, no attempt has been made to include references inside each chapter. This approach was intentional from the start because the basics that were being described were founded on a great deal of knowledge accumulated by very many research workers, and it seemed invidious to single out particular individuals. However, in book form, it was felt that Back-fa-Basics should include a bibliography of mass spectrometry, which a reader could use to follow up and expand on anything gleaned in the various chapters. Tothis end, we have included a list of some 100 textbooks that are now available, at least through libraries. Each title in the list gives agood idea of the book's contents, and the books themselves yield many leading references. The book list covers publications from about 1965, when there were few books on mass spectrometry produced annually, to the present, when it is not unusual to find several books publishedeach year.This growth reflectsthehuge range ofapplicationsofmass spectrometry, engendered by its scope and sensitivity in analysis, and by the variety of excellent commercial instruments now available. The list of books is not meant to be exhaustive, nor is it selective. If any bookauthorreads this introduction and finds that his own book is not on the list, please accept our apologies for an unintended oversight. For readers of this Back-to-Basics volume who want to learn about current advances, we have also included a list ofjournals that deal exclusively with mass spectrometry or contain a significant number of articles on the subject. Anothergood place to catch up on current work lies in the many large and small conferences or meetings that are held each year all over the world. Readers of this Back-to-Basics tome will find that these conferences are good venues for meeting many of the experts in mass spectrometry, where they can be questioned about esoteric aspects of the subject in a friendly and often convivial atmosphere. Who knows, you may even meet the present authors at some meeting and pass on your remarks directly, accompanied by ale, nectar of the gods or Adam's ale! Contents Chapter 1 Chemical Ionization (CI) 1 The Ionization Process 1 Example of the Chemical Ionization Process 1 OtherReagent Gases 2 Other Ionization Routes 3 Usesof CI 4 Useof CIlEI in Tandem in GCIMS 4 NegativeIons 5 Conclusion 5 Chapter 2 Laser Desorption Ionization (LDI) 7 TheIonization Process 7 Other Considerations on Laser Desorption Ionization 9 Useof a Matrix 9 Typesof Laser 10 Secondary Ionization 10 Usesof Lasers 11 Conclusion 12 Chapter 3 Electron Ionization (EI) 13 TheIonization Process 13 Mass-To-Charge Ratio (m/z) 13 The Mass Spectrum 14 The Ion Source 14 Isotopes ,., , , " , , , 16 Conclusion 16 Chapter 4 Fast-Atom Bombardment (FAB) and Liquid-Phase Secondary Ion Mass Spectrometry (LSIMS) Ionization 17 Introduction 17 Atom or Ion Beams 18 The Ionization Process 18 Momentum Transfer 18 Ionization by Electron Transfer 19 Random Fragmentation 20 Properties of the Solvent (Matrix) 20 The Mass Spectrum 21 Conclusion 22