Mass Spectrometry

Second Edition

Mass Spectrometry

A Textbook

Second Edition

123

Foreword by Peter Roepstorff

Jürgen H. Gross

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ISBN 978-3-642-10709-2 e-ISBN 978-3-642-10711-5DOI 10.1007/978-3-642-10711-5Springer Heidelberg Dordrecht London New York

Jürgen H. GrossInstitute of Organic ChemistryHeidelberg UniversityIm Neuenheimer Feld 27069120 HeidelbergGermanyemail: author@ms-textbook.com

Foreword

Shortly after having graduated in 1966 and just employed as a research assistant in a protein chemistry laboratory, my very first contact with mass spectrometry hap-pened when I stumbled on a paper by Michael Barber, the later discoverer of fast atom bombardment (FAB). Together with a French group he had determined the covalent structure of an almost 1.4 kDa complex peptidolipid called fortuitine by using mass spectrometry. Fascinated by this to me unknown technique, I felt that MS would be a future key analytical method in protein studies. At that time, the only ionization method available was electron ionization, which required a sample to be in the gaseous state in the ion source. Therefore most mass spectrometric analyses were dealing with small organic molecules – and peptides and proteins were not volatile. Fortuitine was a very fortuitous sample, because it was naturally derivatized with the consequence that it could be volatilized into the ion source. Nevertheless, I went into mass spectrometry. My first mass spectrometer was in-stalled in our laboratory in 1968. Mass spectrometers at that time were complex fully manually operated instruments most of them magnetic/electrostatic sector in-struments, and the operator needed to know the instrument well in order to avoid catastrophes by opening wrong valves at the wrong moment. Spectra were re-corded on UV paper with a galvanometer recorder or on photographic plates and mass assignment was performed manually. During the 1970s a number of new ionization methods and mass analyzers became available. These included ioniza-tion by chemical ionization and by field ionization/desorption as well as mass analyses by quadrupoles and ion traps. Computers became available for data ac-quisition and mass assignment. Life became easier but the requirement for volatile samples was still there.

The 1980s revolutionized the possibilities for mass spectrometric analysis. In the early half of the decade introduction of FAB and commercialization of the 10 years earlier developed plasma desorption mass spectrometry allowed for analyses of nonvolatile samples such as peptides, proteins, and nucleic acids. The first commercial fully automated mass spectrometer, the BioIon plasma desorption mass spectrometer, became available and the time-of-flight analyzer, which had unlimited mass range, was revived. Late in the decade the two new and now dominating ionization methods electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) were introduced. These two ionization meth-ods opened a new era for mass spectrometry. Now all the large nonvolatile bio-logical molecules could be analyzed. Till then GC-MS had been extensively used for analysis of complex mixtures in environmental and clinical sciences, but due to its nature it was limited to small volatile molecules. ESI made coupling of LC with MS possible allowing for entirely new applications of mass spectrometry. Proteomics now became a big move forward with mass spectrometry as the key analytical tool. Thousands of scientists took up mass spectrometric analysis and

VI Foreword

the instrument manufacturers realized that a new market had emerged and that the new generation of users were different from the previous technically skilled spe-cialists. The new generation of instruments therefore became computer controlled, equipped with safety features to avoid any erroneous operation and with fully computerized data acquisition. The requirement from the biological sciences for high speed, sensitivity, and mass accuracy resulted in dramatic improvements of the performance of the instruments. Hybrid instruments combining the well-known mass analyzers were constructed, the FT-ICR mass spectrometer, which till then had only been available in highly specialized mass spectrometry laboratories, moved into the biological laboratory. Lately, the orbitrap analyzer, also based on Fourier transformation, has become standard in advanced biological research labo-ratories. Biological mass spectrometry and especially analysis of proteins and pro-teomics now dominate mass spectrometry conferences and mass spectrometry has a strong position in biological conferences, where these subjects ten years earlier were only marginally present.

What are the consequences of this development? For me, having tried to get mass spectrometry into protein science for more than 40 years it is of course en-couraging. Mass spectrometry is without any doubt now the most versatile ana-lytical technique available. It is used in a wide variety of areas from inorganic, nu-clear chemistry, and geochemistry over organic chemistry, environmental analyses, clinical chemistry, to molecular and cell biology. Online separation of complex mixtures is possible using either GC-MS or LC-MS. Almost all commer-cial instruments are highly automated. However, this development also rises seri-ous concerns. Many of the new users consider the mass spectrometer as a black box where they put in the sample in one end and get a result from the computer in the other end. They do not or only marginally understand the principles in their in-strument and rarely look at the raw data. They are satisfied with computer prints with lists of identified compounds. Sample preparation often follows standard pro-tocols and the understanding of the need for optimized sample preparation for each analytical task is often ignored. As a result, a considerable amount of the data obtained are questionable either due to poor sample preparation, poor instrument performance, or suboptimal use of the instruments. It is my wish that the new gen-eration of mass spectrometry users will spend time to understand their instruments and the requirements for optimal preparation of the samples and it is my hope that this book will be read by many of them so that they can use their techniques to the best of the equipment’s potential. Odense, 2010 Peter Roepstorff Department of Biochemistry and Molecular Biology University of Southern Denmark

Preface to the Second Edition

To all readers of the first edition of Mass Spectrometry – A Textbook I would like to express my deepest gratitude. Without their interest in wanting to learn more about mass spectrometry by use of this book, all the efforts in writing it would have been a mere waste of time, and moreover, without their demand for updates, there would be no next edition. I would also like to thank the instructors all over the world who adopted and recommended this book for their own mass spectrome-try courses.

Preparing the second edition of Mass Spectrometry – A Textbook was not an easy task. The years have witnessed a flood of innovations and detailed knowl-edge of interrelationships that were previously hardly understood. The time be-tween the editions may have appeared a bit long for many eager scholars. But the author has used the time effectively to improve and update the entire contents, hopefully to the benefit of all who have been patiently bearing with me in antici-pation.

So, what’s new? The book now comprises fifteen instead of twelve chapters, each of them headed by essential “Learning Objectives”. Chapter 9 inserts meth-ods of ion activation such as CID, ECD, ETD, and IRMPD closely related to the instrumental approaches to tandem mass spectrometry. A second additional chap-ter deals with sampling and ion generation from surfaces under ambient conditions as afforded by DART and DESI, to name the most relevant methods. Finally, a new chapter on inorganic mass spectrometry has been added, for one, to include element speciation that bridges the gap between biomedical and trace elemental analysis and, also, to open a perspective extending beyond the key topics of this book. The chapter on instrumentation has been significantly expanded to cover or-bitrap, linear ion traps, TOF/TOF, FT-ICR, and the ever-changing hybrid instru-ments including IMS-MS systems. More detailed attention is drawn to applica-tions regarding biopolymers, especially in those chapters dealing with MALDI and ESI.

Overall, the book has been expanded by more than 200 pages. No chapter has remained untouched. Numerous passages have been rewritten to improve the clar-ity of explanations while keeping them short and concise. Care has been taken not only to explain how, but also to why things are done a certain way. Several schemes have been added to clarify interrelationships between different tech-niques. Tables compiling data for general reference where transferred to the ex-panded appendix. The book’s website has been updated providing new exercises and supplementary material (http://www.ms-textbook.com).

VIII Preface to the Second Edition

Many kind people have supported me in the process of compiling this second edition. I appreciate the detailed knowledge and great thoroughness of Kenzo Hi-raoka, Yasuhide Naito, Takemichi Nakamura, and Hiroaki Sato allocated to the translation of the first edition into Japanese. The valuable and welcome comments from readers from all over the world, and in particular, from book reviewers and colleagues have revealed some shortcomings in the first edition, which now have been eliminated to the improvement of the resulting new edition.

As in the first edition, several well-respected colleagues have contributed to this book by carefully checking contents in their fields of expertise. For the second edition, I want to express special thanks to Jürgen Grotemeyer, Universität Kiel, for checking Chap. 2 (Principles of Ionization and Ion Dissociation), Alexander Makarov, Thermo Fisher Scientific, Bremen (Chap. 4, Instrumentation), Christoph A. Schalley, Freie Universität Berlin (Chap. 9, Tandem Mass Spectrometry), Belá Paizs, German Cancer Research Center, Heidelberg (Chap. 11, Matrix-Assisted Laser Desorption/Ionization), Zoltán Takáts, Universität Gießen (Chap. 13, Ambi-ent Mass Spectrometry), and Detlef Günther, ETH Zürich (Chap. 15, Inorganic Mass Spectrometry). Without their care and help the many new parts would not have reached the present level of accuracy. Despite intense reviewing and proof-reading some errors inevitably may have remained. I apologize for these in ad-vance and would highly appreciate any feedback from the readership in trying to identify and correcting them.

I am indebted to Peter Roepstorff, Odense University, for writing the Foreword with such a personal connotation. Permission to prepare this 2nd edition, alongside my official professional duties, by A. Stephen K. Hashmi, Director of OCI, and Heinfried Schöler, Dean of the Faculty of Chemistry and Earth Sciences is sin-cerely acknowledged. Many thanks to Doris Lang, Iris Mitsch, and Norbert Nieth, for smoothly running the routine analyses in our MS facility. And again, several mass spectrometry companies are acknowledged for supplying new instrument schemes and other figures for inclusion in the 2nd edition. Theodor C. H. Cole ac-complished a great job in polishing up my English. Finally, I am immeasurably grateful to my family for their patience and solidarity in times when I had to come home late or needed to vanish on Saturdays during the writing of this book.

Have a good time studying, learning, and enjoying the world of massspectrometry!

Heidelberg, 2010

Jürgen H. Gross Institute of Organic Chemistry Heidelberg University Im Neuenheimer Feld 270 69120 Heidelberg Germany email: author@ms-textbook.com

Preface

When non-mass spectrometrists are talking about mass spectrometry it rather often sounds as if they were telling a story out of Poe's Tales of Mystery and Imagina-tion. Indeed, mass spectrometry appears to be regarded as a mysterious method, just good enough to supply some molecular weight information. Unfortunately, this rumor about the dark side of analytical methods reaches students much earlier than their first contact with mass spectrometry. Possibly, some of this may have been bred by mass spectrometrists themselves who tended to celebrate each mass spectrum they obtained from the gigantic machines of the early days. Of course, there were also those who enthusiastically started in the 1950s to develop mass spectrometry out of the domain of physics to become a new analytical tool for chemistry.

Nonetheless, some oddities remain and the method which is to be introduced herein is not always straightforward and easy. If you had asked me, the author, just after having finished my introductory course whether mass spectrometry would become my preferred area of work, I surely would have strongly denied. On the other hand, J. J. Veith's mass spectrometry laboratory at Darmstadt Univer-sity was bright and clean, had no noxious odors, and thus presented a nice contrast to a preparative organic chemistry laboratory. Numerous stainless steel flanges and electronics cabinets were tempting to be explored and – whoops – infected me with CMSD (chronic mass spectrometry disease). Staying with Veith's group slowly transformed me into a mass spectrometrist. Inspiring books such as Fundamental Aspects of Organic Mass Spectrometry or Metastable Ions, out of stock even in those days, did help me very much during my metamorphosis. Hav-ing completed my doctoral thesis on fragmentation pathways of isolated immo-nium ions in the gas phase, I assumed my current position. Since 1994, I have been head of the mass spectrometry laboratory at the Chemistry Department of Heidelberg University where I teach introductory courses and seminars on mass spectrometry.

When students ask what books to read on mass spectrometry, there are various excellent monographs, but the ideal textbook still seemed to be missing – at least in my opinion. Finally, encouraged by many people including P. Enders, Springer-Verlag Heidelberg, two years of writing began.

The present volume would not have its actual status without the critical reviews of the chapters by leading experts in the field. Their thorough corrections, re-marks, and comments were essential. Therefore, P. Enders, Springer-Verlag Hei-delberg (Introduction), J. Grotemeyer, University of Kiel (Gas Phase Ion Chemis-try), S. Giesa, Bayer Industry Services, Leverkusen (Isotopes), J. Franzen, Bruker

X Preface

Daltonik, Bremen (Instrumentation), J. O. Metzger, University of Oldenburg (Electron Ionization and Fragmentation of Organic Ions and Interpretation of EI Mass Spectra), J. R. Wesener, Bayer Industry Services, Leverkusen (Chemical Ionization), J. J. Veith, Technical University of Darmstadt (Field Desorption), R. M. Caprioli, Vanderbilt University, Nashville (Fast Atom Bombardment), M. Karas, University of Frankfurt (Matrix-Assisted Laser Desorption/Ionization), M. Wilm, European Molecular Biology Laboratory, Heidelberg (Electrospray Ionization) and M. W. Linscheid, Humboldt University, Berlin (Hyphenated Methods) deserve my deep gratitude.

Many manufacturers of mass spectrometers and mass spectrometry supply are gratefully acknowledged for sending large collections of schemes and photographs for use in this book. The author wishes to express his thanks to those scientists, many of them from the University of Heidelberg, who generously allowed to use material from their actual research as examples and to those publishers, who granted the numerous copyrights for use of figures from their publications. The generous permission of the National Institute of Standards and Technology (G. Mallard, J. Sauerwein) to use a large set of electron ionization mass spectra from the NIST/EPA/NIH Mass Spectral Library is also gratefully acknowledged. My thanks are extended to the staff of my facility (N. Nieth, A. Seith, B. Flock) for their efforts and to the staff of the local libraries for their friendly support. I am indebted to the former director of our institute (R. Gleiter) and to the former dean of our faculty (R. N. Lichtenthaler) for permission to write a book besides my of-ficial duties.

Despite all efforts, some errors or misleading passages will still have remained. Mistakes are an attribute that make us human, but unfortunately, they do not con-tribute to the scientific or educational value of a textbook. Therefore, please do not hesitate to report errors to me or to drop a line of comment in order to allow for corrections in a future edition.

Hopefully, Mass Spectrometry – A Textbook will introduce you to the manyfacets of mass spectrometry and will satisfy your expectations.

Heidelberg, 2003

Jürgen H. Gross Institute of Organic Chemistry Heidelberg University Im Neuenheimer Feld 270 69120 Heidelberg Germany email: author@ms-textbook.com

Table of Contents

Table of Contents................................................................................................ XI

1 Introduction ........................................................................................................1 Learning Objectives ......................................................................................1

1.1 Aims and Scope ...........................................................................................3 1.1.1 Filling the Black Box ...........................................................................5

1.2 What Is Mass Spectrometry? .......................................................................5 1.2.1 Mass Spectrometry ...............................................................................6 1.2.2 Mass Spectrometer ...............................................................................7 1.2.3 Mass Scale............................................................................................8 1.2.4 Mass Spectrum .....................................................................................9

1.3 Ion Chromatograms ...................................................................................11 1.4 Performance of Mass Spectrometers..........................................................13

1.4.1 Sensitivity...........................................................................................13 1.4.2 Detection Limit ..................................................................................14 1.4.3 Signal-to-Noise Ratio .........................................................................14

1.5 Terminology – General Aspects ................................................................15 1.5.1 Basic Terminology in Describing Mass Spectra ................................16

1.6 Units, Physical Quantities, and Physical Constants ...................................17 References........................................................................................................17

2 Principles of Ionization and Ion Dissociation.................................................21 Learning Objectives ....................................................................................21

2.1 Gas Phase Ionization by Energetic Electrons.............................................21 2.1.1 Formation of Ions ...............................................................................22 2.1.2 Processes Accompanying Electron Ionization....................................23 2.1.3 Ions Generated by Penning Ionization................................................24 2.1.4 Ionization Energy ...............................................................................25 2.1.5 Ionization Energy and Charge-Localization.......................................25

2.2 Vertical Transitions....................................................................................27 2.3 Ionization Efficiency and Ionization Cross Section...................................29

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2.4 Internal Energy and the Further Fate of Ions ............................................. 30 2.4.1 Degrees of Freedom ........................................................................... 31 2.4.2 Appearance Energy ............................................................................ 32 2.4.3 Bond Dissociation Energies and Heats of Formation......................... 33 2.4.4 Randomization of Energy................................................................... 35

2.5 Quasi-Equilibrium Theory......................................................................... 37 2.5.1 QET’s Basic Premises........................................................................ 37 2.5.2 Basic QET .......................................................................................... 38 2.5.3 Rate Constants and Their Meaning .................................................... 39 2.5.4 k(E) Functions – Typical Examples ..................................................... 40 2.5.5 Reacting Ions Described by k(E) Functions ......................................... 40 2.5.6 Direct Cleavages and Rearrangement Fragmentations....................... 40

2.6 Time Scale of Events ................................................................................. 42 2.6.1 Stable, Metastable, and Unstable Ions................................................ 43 2.6.2 Time Scale of Ion Storage Devices .................................................... 44

2.7 Internal Energy – Practical Implications.................................................... 45 2.8 Reverse Reactions and Kinetic Energy Release ........................................ 46

2.8.1 Activation Energy of the Reverse Reaction ....................................... 46 2.8.2 Kinetic Energy Release ...................................................................... 48 2.8.3 Energy Partitioning ............................................................................ 49

2.9 Isotope Effects ........................................................................................... 49 2.9.1 Primary Kinetic Isotope Effects ......................................................... 50 2.9.2 Measurement of Isotope Effects......................................................... 51 2.9.3 Secondary Kinetic Isotope Effects ..................................................... 53

2.10 Determination of Ionization Energies...................................................... 54 2.10.1 Conventional Determination of Ionization Energies ........................ 54 2.10.2 Improved IE Accuracy from Data Post-Processing.......................... 54 2.10.3 IE Accuracy – Experimental Improvements .................................... 55 2.10.4 Photoionization Processes ................................................................ 55

2.11 Determining the Appearance Energies .................................................... 58 2.11.1 Kinetic Shift ..................................................................................... 58 2.11.2 Breakdown Graphs........................................................................... 59

2.12 Gas Phase Basicity and Proton Affinity................................................... 61 References ....................................................................................................... 62

3 Isotopic Composition and Accurate Mass ...................................................... 67 Learning Objectives .................................................................................... 67

3.1 Isotopic Classification of the Elements...................................................... 67 3.1.1 Monoisotopic Elements ..................................................................... 68 3.1.2 Di-isotopic Elements .......................................................................... 68 3.1.3 Polyisotopic Elements ........................................................................ 69 3.1.4 Representation of Isotopic Abundances ............................................. 69 3.1.5 Calculation of Atomic, Molecular, and Ionic Mass............................ 71 3.1.6 Natural Variations in Relative Atomic Mass...................................... 73

3.2 Calculation of Isotopic Distributions ......................................................... 74 3.2.1 Carbon: An X+1 Element................................................................... 74

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3.2.2 Terms Related to Isotopic Composition .............................................77 3.2.3 Binomial Approach ............................................................................77 3.2.4 Halogens.............................................................................................78 3.2.5 Combinations of Carbon and Halogens..............................................80 3.2.6 Polynomial Approach.........................................................................81 3.2.7 Oxygen, Silicon, and Sulfur ...............................................................81 3.2.8 Polyisotopic Elements ........................................................................84 3.2.9 Practical Aspects of Isotopic Patterns ................................................84 3.2.10 Bookkeeping with Isotopic Patterns in Mass Spectra.......................85 3.2.11 Information from Complex Isotopic Patterns ...................................86

3.3 Isotopic Enrichment and Isotopic Labeling ...............................................87 3.3.1 Isotopic Enrichment ...........................................................................87 3.3.2 Isotopic Labeling................................................................................88

3.4 Resolution and Resolving Power ...............................................................88 3.4.1 Definitions..........................................................................................88 3.4.2 Resolution and its Experimental Determination.................................90 3.4.3 Resolving Power and its Effect on Relative Peak Intensity................91

3.5 Accurate Mass ...........................................................................................92 3.5.1 Exact Mass and Molecular Formulas .................................................92 3.5.2 Mass Defect........................................................................................93 3.5.3 Mass Accuracy ...................................................................................95 3.5.4 Accuracy and Precision ......................................................................96 3.5.5 Mass Accuracy and the Determination of Molecular Formulas .........97 3.5.6 Extreme Mass Accuracy – Special Considerations ............................98

3.6 Applied High-Resolution Mass Spectrometry ...........................................99 3.6.1 External Mass Calibration ..................................................................99 3.6.2 Internal Mass Calibration .................................................................101 3.6.3 Compiling Mass Reference Lists......................................................103 3.6.4 Specification of Mass Accuracy.......................................................104 3.6.5 Deltamass .........................................................................................104 3.6.6 Kendrick Mass Scale ........................................................................105 3.6.7 Van Krevelen Diagrams ...................................................................106

3.7 Resolution Interacting with Isotopic Patterns ..........................................107 3.7.1 Multiple Isotopic Compositions at Very High Resolution ...............107 3.7.2 Isotopologs and Accurate Mass........................................................110 3.7.3 Large Molecules – Isotopic Patterns at Sufficient Resolution..........110 3.7.4 Large Molecules – Isotopic Patterns at Low Resolution.......... 112

3.8 Charge State and Interaction with Isotopic Patterns ................................112 References......................................................................................................114

4 Instrumentation ..............................................................................................117 Learning Objectives ..................................................................................117

4.1 How to Create a Beam of Ions.................................................................119 4.2 Time-of-Flight Instruments......................................................................120

4.2.1 Time-of-Flight – Basic Principles ....................................................120 4.2.2 TOF Instruments – Velocity of Ions and Time-of-Flight .................121 4.2.3 Linear Time-of-Flight Analyzer .......................................................123

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4.2.4 Reflector Time-of-Flight Analyzer .................................................. 126 4.2.5 Higher Vacuum Improves Resolving Power.................................... 128 4.2.6 Delay Before Extraction to Improve Resolving Power .................... 128 4.2.7 Analog-to-Digital Conversion.......................................................... 131 4.2.8 Orthogonal Acceleration TOF Analyzers......................................... 132 4.2.9 Operation of the oaTOF Analyzer.................................................... 133 4.2.10 Duty Cycle ..................................................................................... 134 4.2.11 Time-to-Digital Conversion ........................................................... 135

4.3 Magnetic Sector Instruments ................................................................... 135 4.3.1 Evolution of Magnetic Sector Instruments....................................... 135 4.3.2 Principle of the Magnetic Sector ...................................................... 136 4.3.3 Focusing Action of the Magnetic Field ............................................ 138 4.3.4 Double-Focusing Sector Instruments ............................................... 139 4.3.5 Geometries of Double-Focusing Sector Instruments........................ 141 4.3.6 Adjusting the Resolving Power of a Sector Instrument.................... 143 4.3.7 Innovations in Sector Instruments.................................................... 144

4.4 Linear Quadrupole Instruments ............................................................... 146 4.4.1 Introduction ...................................................................................... 146 4.4.2 The Linear Quadrupole .................................................................... 147 4.4.3 Resolving Power of Linear Quadrupoles ......................................... 151 4.4.4 RF-Only Quadrupoles, Hexapoles, and Octopoles........................... 152

4.5 Linear Quadrupole Ion Traps................................................................... 155 4.5.1 Linear RF-Only Multipole Ion Traps ............................................... 155 4.5.2 Mass-Analyzing Linear Quadrupole Ion Trap with Axial Ejection . 158 4.5.3 Mass-Analyzing Linear Ion Trap with Radial Ejection.................... 160

4.6 Three-Dimensional Quadrupole Ion Trap................................................ 164 4.6.1 Introduction ...................................................................................... 164 4.6.2 The Quadrupole Ion Trap................................................................. 164 4.6.3 Visualization of Ion Motion in the Ion Trap .................................... 167 4.6.4 Mass-Selective Stability Mode......................................................... 168 4.6.5 Mass-Selective Instability Mode ...................................................... 168 4.6.6 Resonant Ejection............................................................................. 169 4.6.7 Axial Modulation and Automatic Gain Control ............................... 170 4.6.8 Nonlinear Resonances ...................................................................... 171 4.6.9 Digital Waveform Quadrupole Ion Trap .......................................... 172 4.6.10 External Ion Sources for the Quadrupole Ion Trap ........................ 173

4.7 Fourier Transform Ion Cyclotron Resonance .......................................... 174 4.7.1 Ion Cyclotron Resonance ................................................................. 174 4.7.2 Ion Cyclotron Motion....................................................................... 174 4.7.3 Cyclotron Motion – Excitation and Detection.................................. 175 4.7.4 Cyclotron Frequency Bandwidth and Energy-Time Uncertainty ..... 177 4.7.5 Fourier Transform – Basic Properties .............................................. 179 4.7.6 Nyquist Criterion.............................................................................. 181 4.7.7 Excitation Modes in FT-ICR-MS..................................................... 182 4.7.8 Axial Trapping and Design of ICR Cells ......................................... 183 4.7.9 Magnetron Motion and Reduced Cyclotron Frequency ................... 184

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4.7.10 Detection and Accuracy in FT-ICR-MS.........................................186 4.7.11 FT-ICR Instruments .......................................................................187

4.8 Orbitrap Analyzer ....................................................................................189 4.8.1 Orbitrap – Principle of Operation.....................................................189 4.8.2 Ion Detection and Resolving Power of the Orbitrap ........................191 4.8.3 Ion Injection into the Orbitrap..........................................................192 4.8.4 Hybridization with a Linear Quadrupole Ion Trap ...........................193

4.9 Hybrid Instruments ..................................................................................194 4.9.1 Evolution of Hybrid Mass Spectrometers.........................................196 4.9.2 Ion Mobility-Mass Spectrometry Systems .......................................198

4.10 Detectors ................................................................................................202 4.10.1 Discrete Dynode Electron Multipliers............................................203 4.10.2 Channel Electron Multipliers .........................................................204 4.10.3 Microchannel Plates .......................................................................205 4.10.4 Post-Acceleration and Conversion Dynode....................................206 4.10.5 Focal Plane Detectors .....................................................................207

4.11 Vacuum Technology..............................................................................208 4.11.1 Basic Mass Spectrometer Vacuum System ....................................209 4.11.2 High Vacuum Pumps......................................................................209

4.12 Purchasing an Instrument.......................................................................210 References......................................................................................................210

5 Practical Aspects of Electron Ionization.......................................................223 Learning Objectives ..................................................................................223

5.1 Electron Ionization Ion Sources...............................................................223 5.1.1 Layout of an Electron Ionization Ion Source....................................223 5.1.2 Generation of Primary Electrons ......................................................225 5.1.3 Overall Efficiency and Sensitivity of an El Ion Source....................226 5.1.4 Optimization of Ion Beam Geometry ...............................................227

5.2 Sample Introduction.................................................................................228 5.2.1 Reservoir or Reference Inlet System................................................228 5.2.2 Direct Insertion Probe ......................................................................231 5.2.3 Sample Vials for Use with Direct Insertion Probes..........................232 5.2.4 Fractionation When Using Direct Insertion Probes..........................233 5.2.5 Direct Exposure Probe......................................................................235

5.3 Pyrolysis Mass Spectrometry...................................................................237 5.4 Gas Chromatograph .................................................................................237 5.5 Liquid Chromatograph.............................................................................238 5.6 Low-Energy Electron Ionization Mass Spectra .......................................239 5.7 Analytes for EI.........................................................................................241 5.8 Mass Analyzers for EI .............................................................................241 5.9 Mass Spectral Databases for EI ...............................................................242

5.9.1 NIST/EPA/NIH Mass Spectral Database .........................................243 5.9.2 Wiley Registry of Mass Spectral Data .............................................244 5.9.3 Mass Spectral Databases – General Aspects ....................................244

References......................................................................................................245

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6 Fragmentation of Organic Ions and Interpretation of EI Mass Spectra... 249 Learning Objectives .................................................................................. 249

6.1 Cleavage of a Sigma-Bond ...................................................................... 250 6.1.1 Writing Conventions for Molecular Ions ......................................... 250 6.1.2 σ-Bond Cleavage in Small Nonfunctionalized Molecules ............... 251 6.1.3 Even-Electron Rule .......................................................................... 252 6.1.4 σ-Bond Cleavage in Small Functionalized Molecules ..................... 254

6.2 Alpha-Cleavage ....................................................................................... 255 6.2.1 α-Cleavage of Acetone Molecular Ion............................................. 255 6.2.2 Stevenson's Rule............................................................................... 257 6.2.3 α-Cleavage of Nonsymmetrical Aliphatic Ketones.......................... 259 6.2.4 Acylium Ions and Carbenium Ions................................................... 260 6.2.5 α-Cleavage When Heteroatoms Belong to the Aliphatic Chain....... 262 6.2.6 α-Cleavage of Aliphatic Amines...................................................... 262 6.2.7 Nitrogen Rule ................................................................................... 265 6.2.8 α-Cleavage of Aliphatic Ethers and Alcohols.................................. 266 6.2.9 Charge Retention at the Heteroatom ................................................ 268 6.2.10 α-Cleavage of Thioethers............................................................... 269 6.2.11 α-Cleavage of Halogenated Hydrocarbons .................................... 269 6.2.12 Double α-Cleavage ........................................................................ 271 6.2.13 Double α-Cleavage for the Identification of Regioisomers ........... 272

6.3 Distonic Ions............................................................................................ 273 6.3.1 Definition of Distonic Ions............................................................... 273 6.3.2 Formation and Properties of Distonic Ions....................................... 274 6.3.3 Distonic Ions as Intermediates ......................................................... 275

6.4 Benzylic Bond Cleavage.......................................................................... 275 6.4.1 Cleavage of the Benzylic Bond in Phenylalkanes ............................ 275 6.4.2 The Further Fate of [C6H5]

+ and [C7H7]+.......................................... 277

6.4.3 Isomerization of [C7H8]+• and [C8H8]

+• Ions..................................... 279 6.4.4 Rings Plus Double Bonds................................................................. 280

6.5 Allylic Bond Cleavage............................................................................. 281 6.5.1 Cleavage of the Allylic Bond in Aliphatic Alkenes ......................... 281 6.5.2 Methods for the Localization of the Double Bond ........................... 283

6.6. Cleavage of Non-Activated Bonds ......................................................... 284 6.6.1 Saturated Hydrocarbons ................................................................... 284 6.6.2 Carbenium Ions ................................................................................ 286 6.6.3 Very Large Hydrocarbons................................................................ 287 6.6.4 Recognition of the Molecular Ion Peak............................................ 288

6.7 McLafferty Rearrangement...................................................................... 290 6.7.1 McL of Aldehydes and Ketones....................................................... 290 6.7.2 Fragmentation of Carboxylic Acids and Their Derivatives.............. 293 6.7.3 McL of Aromatic Hydrocarbons ...................................................... 296 6.7.4 McL with Double Hydrogen Transfer.............................................. 297

6.8 Retro-Diels-Alder Reaction ..................................................................... 300 6.8.1 Properties of the Retro-Diels-Alder Reaction .................................. 300

XVII

6.8.2 Influence of Positional Isomerism on the RDA Reaction.................302 6.8.3 RDA Reaction in Natural Products ..................................................303 6.8.4 Widespread Occurrence of the RDA Reaction.................................303

6.9 Elimination of Carbon Monoxide ............................................................304 6.9.1 CO Loss from Phenols .....................................................................304 6.9.2 CO and C2H2 Loss from Quinones ...................................................307 6.9.3 Fragmentation of Arylalkylethers.....................................................308 6.9.4 CO Loss from Transition Metal Carbonyl Complexes.....................310 6.9.5 CO Loss from Carbonyl Compounds ...............................................311 6.9.6 Differentiation Between Loss of CO, N2, and C2H4 .........................311

6.10 Thermal Degradation vs. Ion Fragmentation .........................................312 6.10.1 Decarbonylation and Decarboxylation ...........................................312 6.10.2 Retro-Diels-Alder Reaction............................................................312 6.10.3 Loss of H2O from Alkanols ............................................................312 6.10.4 EI Mass Spectra of Organic Salts ...................................................314

6.11 Alkene Loss from Onium Ions...............................................................315 6.11.1 McL of Onium Ions........................................................................316 6.11.2 Onium Reaction..............................................................................319

6.12 Ion-Neutral Complexes..........................................................................322 6.12.1 Evidence for the Existence of Ion-Neutral Complexes ..................322 6.12.2 Attractive Forces in Ion-Neutral Complexes..................................323 6.12.3 Criteria for Ion-Neutral Complexes................................................324 6.12.4 Ion-Neutral Complexes of Radical Ions .........................................325

6.13 Ortho Elimination (Ortho Effect) ..........................................................326 6.13.1 Ortho Elimination from Molecular Ions.........................................327 6.13.2 Ortho Elimination from Even-Electron Ions ..................................328 6.13.3 Ortho Elimination in the Fragmentation of Nitroarenes ..........331

6.14 Heterocyclic Compounds.......................................................................332 6.14.1 Saturated Heterocyclic Compounds ...............................................333 6.14.2 Aromatic Heterocyclic Compounds ...............................................336

6.15 Guide to the Interpretation of Mass Spectra ..........................................340 6.15.1 Summary of Rules ..........................................................................340 6.15.2 Systematic Approach to Mass Spectra ...........................................341

References......................................................................................................342

7 Chemical Ionization........................................................................................351 Learning Objectives ..................................................................................351

7.1 Basics of Chemical Ionization .................................................................351 7.1.1 Formation of Ions in Positive-Ion Chemical Ionization ...................351 7.1.2 Chemical Ionization Ion Sources......................................................352 7.1.3 Sensitivity of Chemical Ionization ...................................................353 7.1.4 Chemical Ionization Techniques and Terms ....................................353

7.2 Protonation in Chemical Ionization .........................................................354 7.2.1 Source of Protons .............................................................................354 7.2.2 Methane Reagent Gas Plasma ..........................................................355 7.2.3 CH5

+ and Related Ions......................................................................356

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7.2.4 Energetics of Protonation ................................................................. 356 7.2.5 Impurities of Higher PA than the Reagent Gas ................................ 357 7.2.6 Methane Reagent Gas PICI Spectra ................................................. 358 7.2.7 Other Reagent Gases in PICI............................................................ 359

7.3 Proton Transfer Reaction Mass Spectrometry ......................................... 361 7.3.1 Reactant Ion Formation in PTR-MS ................................................ 362 7.3.2 Analyte Ion Formation in PTR-MS.................................................. 362

7.4 Charge Exchange Chemical Ionization.................................................... 364 7.4.1 Energetics of CE .............................................................................. 365 7.4.2 Reagent Gases for CE-CI ................................................................. 365 7.4.3 Compound Class-Selective CE-CI ................................................... 366 7.4.4 Regio- and Stereoselectivity in CE-CI ............................................. 368

7.5 Negative-Ion Chemical Ionization........................................................... 368 7.6 Electron Capture ...................................................................................... 370

7.6.1 Ion Formation by Electron Capture.................................................. 370 7.6.2 Energetics of EC .............................................................................. 370 7.6.3 Creating Thermal Electrons ............................................................. 372 7.6.4 Appearance of EC Spectra ............................................................... 373 7.6.5 Applications of EC........................................................................... 373

7.7 Desorption Chemical Ionization .............................................................. 374 7.8 Analytes for CI ........................................................................................ 375 References ..................................................................................................... 376

8 Field Ionization and Field Desorption .......................................................... 381 Learning Objectives .................................................................................. 381

8.1 Field Ionization Process........................................................................... 382 8.2 FI and FD Ion Sources............................................................................. 383 8.3 Field Emitters .......................................................................................... 385

8.3.1 Blank Metal Wires as Emitters......................................................... 385 8.3.2 Activated Emitters............................................................................ 385 8.3.3 Emitter Temperature ........................................................................ 386 8.3.4 Handling of Activated Emitters........................................................ 387

8.4 Field Ionization Mass Spectrometry ........................................................ 388 8.4.1 Origin of [M+H]+ Ions in FI-MS...................................................... 389 8.4.2 Multiply-Charged Ions in FI-MS ..................................................... 389 8.4.3 Field-Induced Dissociation .............................................................. 390 8.4.4 Accurate Mass FI Spectra ................................................................ 390 8.4.5 Coupling Gas Chromatography to FI-MS ........................................ 391

8.5 FD Spectra ............................................................................................... 392 8.5.1 Ion Formation by Field Ionization in FD-MS .................................. 393 8.5.2 Desorption of Preformed Ions in FD-MS......................................... 394 8.5.3 Cluster Ion Formation in FD-MS ..................................................... 396 8.5.4 FD-MS of Ionic Analytes ................................................................. 397 8.5.5 Best Anode Temperature and Thermal Decomposition ................... 399 8.5.6 FD-MS of Polymers ......................................................................... 400 8.5.7 Types of Ions in FD-MS................................................................... 401

XIX

8.6 Liquid Injection Field Desorption Ionization...........................................402 8.7 General Properties of FI-MS and FD-MS................................................405

8.7.1 Sensitivity of FI-MS and FD-MS .....................................................405 8.7.2 Analytes and Practical Considerations for FI, FD, and LIFDI .........407 8.7.3 Mass Analyzers for FI and FD .........................................................407

References......................................................................................................408

9 Tandem Mass Spectrometry..........................................................................415 Learning Objectives ..................................................................................415

9.1 Concepts of Tandem Mass Spectrometry ................................................415 9.1.1 Tandem-in-Space and Tandem-in-Time...........................................416 9.1.2 Pictograms for MS/MS Experiments................................................418

9.2 Metastable Ion Dissociation.....................................................................420 9.3 Collision-Induced Dissociation................................................................420

9.3.1 Effecting Collisions in a Mass Spectrometer....................................420 9.3.2 Energy Transfer During Collisions...................................................421 9.3.4 Single and Multiple Collisions in CID .............................................424 9.3.5 Time Scale of Ion Activating Processes ...........................................426

9.4 Surface-Induced Dissociation ..................................................................426 9.5 Tandem MS on TOF Instruments ............................................................427

9.5.1 Utilizing a ReTOF for Tandem MS..................................................427 9.5.2 Curved-Field Reflectron...................................................................429 9.5.3 Tandem MS on True Tandem TOF Instruments ..............................429

9.6 Tandem MS with Magnetic Sector Instruments.......................................431 9.6.1 Dissociations in the FFR Preceding the Magnetic Sector.................431 9.6.2 Mass-Analyzed Ion Kinetic Energy Spectra.....................................432 9.6.3 Determination of Kinetic Energy Release ........................................432 9.6.4 B/E = Const. Linked Scan ................................................................434 9.6.5 Additional Linked Scan Functions ...................................................434 9.6.6 Multi-Sector Instruments..................................................................436

9.7 Tandem MS with Linear Quadrupole Analyzers .....................................437 9.7.1 Triple Quadrupole Mass Spectrometers ...........................................437 9.7.2 Scan Modes for Tandem MS with Triple Quadrupole Instruments..438 9.7.3 Penta Quadrupole Instruments .........................................................438

9.8 Tandem MS with the Quadrupole Ion Trap .............................................439 9.9 Tandem MS with Linear Quadrupole Ion Traps ......................................443

9.9.1 Tandem MS on QqLIT Instruments .................................................444 9.9.2 Tandem MS on LITs with Radial Ejection.......................................444

9.10 Tandem MS with Orbitrap Instruments .................................................445 9.10.1 Higher-Energy C-Trap Dissociation...............................................446 9.10.2 Extended LIT-Orbitrap Hybrid Instruments...................................446

9.11 Tandem MS with FT-ICR Instruments – Part I .....................................448 9.11.1 Sustained Off-Resonance Irradiation-CID in ICR Cells.................448

9.12 Infrared Multiphoton Dissociation.........................................................451 9.12.1 IRMPD in QITs and LITs...............................................................452

9.13 Electron Capture Dissociation ...............................................................452

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9.13.1 Principles of Electron Capture Dissociation................................... 452 9.13.2 Peptide Ion Cleavages Upon ECD ................................................. 454

9.14 Tandem MS with FT-ICR Instruments – Part II .................................... 455 9.14.1 IRMPD for Tandem FT-ICR-MS................................................... 455 9.14.2 Infrared Photodissociation Spectroscopy ....................................... 456 9.14.3 Blackbody Infrared Radiative Dissociation.................................... 457 9.14.4 ECD for Tandem FT-ICR-MS ....................................................... 458

9.15 Electron Transfer Dissociation .............................................................. 459 9.16 Electron Detachment Dissociation......................................................... 461 9.17 Summary of Ion Activation Techniques ................................................ 462 9.18 Special Applications of Tandem MS ..................................................... 463

9.18.1 Ion–Molecule Reactions in Catalytic Studies................................. 464 9.18.2 Gas Phase Hydrogen–Deuterium Exchange................................... 464 9.18.3 Determination of Gas Phase Basicities and Proton Affinities ........ 466 9.18.4 Neutralization-Reionization Mass Spectrometry............................ 467

References ..................................................................................................... 468

10 Fast Atom Bombardment ............................................................................ 479 Learning Objectives .................................................................................. 479

10.1 Ion Sources for FAB and LSIMS .......................................................... 480 10.1.1 FAB Ion Sources ............................................................................ 480 10.1.2 LSIMS Ion Sources ........................................................................ 482 10.1.3 FAB Probes .................................................................................... 482

10.2 Ion Formation in FAB and LSIMS ........................................................ 483 10.2.1 Ion Formation from Inorganic Samples ......................................... 483 10.2.2 Ion Formation from Organic Samples............................................ 484

10.3 Liquid Matrices for FAB and LSIMS.................................................... 486 10.3.1 The Role of the Liquid Matrix ....................................................... 486 10.3.2 FAB Matrix Spectra – General Characteristics .............................. 487 10.3.3 Unwanted Reactions in FAB-MS................................................... 487

10.4 Applications of FAB-MS....................................................................... 488 10.4.1 FAB-MS of Analytes of Low to Medium Polarity......................... 488 10.4.2 FAB-MS of Ionic Analytes ............................................................ 490 10.4.3 High-Mass Analytes in FAB-MS ................................................... 491 10.4.4 Accurate Mass Measurements in FAB Mode................................. 492 10.4.5 Continuous-Flow FAB ................................................................... 494 10.4.6 Low-Temperature FAB .................................................................. 495 10.4.7 FAB-MS and Peptide Sequencing.................................................. 496

10.5 FAB and LSIMS – General Characteristics........................................... 496 10.5.1 Sensitivity of FAB-MS................................................................... 496 10.5.2 Types of Ions in FAB-MS.............................................................. 497 10.5.3 Analytes for FAB-MS .................................................................... 497 10.5.4 Mass Analyzers for FAB-MS......................................................... 497

10.6 Massive Cluster Impact ......................................................................... 498 10.7 252Californium Plasma Desorption......................................................... 498 References ..................................................................................................... 499

XXI

11 Matrix-Assisted Laser Desorption/Ionization ............................................507 Learning Objectives ..................................................................................507

11.1 Ion Sources for LDI and MALDI ..........................................................508 11.2 Ion Formation ........................................................................................509

11.2.1 Ion Yield and Laser Fluence...........................................................510 11.2.2 Effect of Laser Irradiation on the Surface ......................................511 11.2.3 Temporal Evolution of a Laser Desorption Plume .........................512 11.2.4 Processes of Ion Formation in MALDI ..........................................513 11.2.5 “Lucky Survivor” Model of Ion Formation....................................514

11.3 MALDI Matrices ...................................................................................516 11.3.1 Role of the Solid Matrix .................................................................516 11.3.2 Matrices in UV-MALDI.................................................................516 11.3.3 Characteristics of MALDI Matrix Spectra .....................................519

11.4 Sample Preparation ................................................................................519 11.4.1 MALDI Target ...............................................................................519 11.4.2 Standard Sample Preparation .........................................................520 11.4.3 Cationization ..................................................................................522 11.4.4 Cation Removal..............................................................................524 11.4.5 Solvent-Free Sample Preparation ...................................................526 11.4.6 Additional Methods of Sample Supply ..........................................527

11.5 Applications of LDI ...............................................................................527 11.6 Applications of MALDI.........................................................................529

11.6.1 Protein Analysis by MALDI-MS ...................................................529 11.6.2 Peptide Sequencing and Proteomics...............................................531 11.6.3 Carbohydrate Analysis by MALDI-MS .........................................536 11.6.4 Oligonucleotide Analysis by MALDI-MS .....................................538 11.6.5 MALDI-MS of Synthetic Polymers ...............................................539

11.7 Special Surfaces to Mimic the Matrix....................................................541 11.7.1 Desorption/Ionization on Silicon....................................................541 11.7.2 Nano-Assisted Laser Desorption/Ionization...................................542 11.7.3 Further Variations of the MALDI Theme ......................................543

11.8 MALDI Imaging ....................................................................................544 11.9 Atmospheric Pressure MALDI ..............................................................546 11.10 General Characteristics of MALDI......................................................547

11.10.1 Sample Consumption and Detection Limit...................................547 11.10.2 Analytes for MALDI ....................................................................547 11.10.3 Types of Ions in LDI and MALDI-MS ........................................548 11.10.4 Mass Analyzers for MALDI-MS..................................................548

References......................................................................................................549

12 Electrospray Ionization................................................................................561 Learning Objectives ..................................................................................561

12.1 Development of ESI and Related Methods............................................562 12.1.1 Atmospheric Pressure Ionization....................................................563 12.1.2 Thermospray...................................................................................564 12.1.3 Electrohydrodynamic Ionization ....................................................565

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12.1.4 Electrospray Ionization .................................................................. 565 12.2 Ion Sources for ESI................................................................................ 566

12.2.1 Basic Design Considerations.......................................................... 566 12.2.2 Adaptation to Different Flow Rates ............................................... 568 12.2.3 Improved Electrospray Configurations .......................................... 569 12.2.4 Advanced Electrospray Interface Designs...................................... 571 12.2.5 Nozzle-Skimmer Dissociation........................................................ 573

12.3 Nanoelectrospray ................................................................................... 574 12.3.1 Practical Considerations for NanoESI............................................ 575 12.3.2 Spray Modes of NanoESI............................................................... 576 12.3.3 Nanoelectrospray from a Chip ....................................................... 577

12.4 Ion Formation in ESI ............................................................................. 578 12.4.1 Formation of the Electrospray Plume............................................. 578 12.4.2 Disintegration of Charged Droplets................................................ 581 12.4.3 Formation of Ions from Charged Droplets ..................................... 582

12.5 Multiply Charged Ions and Charge Deconvolution ............................... 585 12.5.1 Dealing with Multiply Charged Ions.............................................. 585 12.5.2 Mathematical Charge Deconvolution............................................. 587 12.5.3 Computerized Charge Deconvolution ............................................ 588 12.5.4 Hardware Charge Deconvolution................................................... 590 12.5.5 Controlled Charge Reduction in ESI.............................................. 592

12.6 Applications of ESI-MS ........................................................................ 593 12.6.1 ESI-MS of Small Molecules........................................................... 593 12.6.2 ESI of Metal Complexes ................................................................ 594 12.6.3 ESI of Surfactants........................................................................... 596 12.6.4 Oligonucleotides, DNA, and RNA................................................. 596 12.6.5 ESI-MS of Oligosaccharides .......................................................... 599 12.6.6 High-Mass Proteins and Protein Complexes ................................. 600

12.7 Summary of ESI Characteristics............................................................ 601 12.7.1 Sample Consumption ..................................................................... 603 12.7.2 Types of Ions in ESI....................................................................... 603 12.7.3 Mass Analyzers for ESI.................................................................. 603

12.8 Atmospheric Pressure Chemical Ionization........................................... 604 12.8.1 Ion Sources for APCI ..................................................................... 604 12.8.2 Ion Formation in APCI................................................................... 605 12.8.3 APCI Spectra.................................................................................. 605

12.9 Atmospheric Pressure Photoionization .................................................. 608 12.9.1 Ion Formation in APPI ................................................................... 608 12.9.2 APPI Spectra .................................................................................. 610

References ..................................................................................................... 612

13 Ambient Mass Spectrometry ....................................................................... 621 Learning Objectives .................................................................................. 621

13.1 Desorption Electrospray Ionization ....................................................... 622 13.1.1 Experimental Setup for DESI......................................................... 622 13.1.2 Mechanisms of Ion Formation in DESI.......................................... 626

.

XXIII

13.1.3 Analytical Features of DESI...........................................................627 13.2 Desorption Atmospheric Pressure Chemical Ionization ........................631 13.3 Desorption Atmospheric Pressure Photoionization ...............................632 13.4 Other Methods Related to DESI ............................................................634

13.4.1 Desorption Sonic Spray Ionization.................................................635 13.4.2 Extractive Electrospray Ionization .................................................635 13.4.3 Electrospray-Assisted Laser Desorption/Ionization (ELDI)...........637 13.4.4 Laser Ablation Electrospray Ionization..........................................638 13.4.5 Atmospheric Pressure Solids Analysis Probe.................................640

13.5 Direct Analysis in Real Time.................................................................640 13.5.1 Experimental Setup for DART.......................................................640 13.5.2 Ion Formation in DART .................................................................642 13.5.3 Analytical Applications of DART..................................................642

13.6 Overview of Ambient Mass Spectrometry ............................................644 References......................................................................................................645

14 Hyphenated Methods ...................................................................................651 Learning Objectives ..................................................................................651

14.1 Concept of Chromatography-Mass Spectrometry..................................652 14.1.1 Ion Chromatograms........................................................................653 14.1.2 Repetitive Acquisition of Mass Spectra During Elution ................654 14.1.3 Selected Ion Monitoring .................................................................656 14.1.4 Selected Reaction Monitoring ........................................................658

14.2 Quantitation ...........................................................................................659 14.2.1 Quantitation by External Standardization.......................................659 14.2.2 Quantitation by Internal Standardization........................................660 14.2.3 Quantitation by Isotope Dilution ....................................................661 14.2.4 Retention Times of Isotopologs......................................................663

14.3 Gas Chromatography-Mass Spectrometry .............................................663 14.3.1 GC-MS Interfaces...........................................................................663 14.3.2 Volatility and Derivatization ..........................................................664 14.3.3 Column Bleed.................................................................................665 14.3.4 Fast GC-MS....................................................................................667 14.3.5 Multiplexing for Increased Throughput .........................................667

14.4 Liquid Chromatography-Mass Spectrometry.........................................668 14.4.1 Multiplexed LC-ESI-MS................................................................671

14.5 Ion Mobility Spectrometry-Mass Spectrometry.....................................673 14.6 Tandem MS as a Complement to LC-MS .........................................675 14.7 Ultrahigh-Resolution Mass Spectrometry .............................................678 References......................................................................................................680

15 Inorganic Mass Spectrometry .....................................................................685 Learning Objectives ..................................................................................685

15.1 Thermal Ionization Mass Spectrometry .................................................689 15.2 Spark Source Mass Spectrometry ..........................................................691 15.3 Glow Discharge Mass Spectrometry......................................................694

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15.4 Inductively Coupled Plasma Mass Spectrometry .................................. 697 15.4.1 Laser Ablation ICP-MS.................................................................. 700

15.5 Secondary Ion Mass Spectrometry ........................................................ 701 15.5.1 Atomic SIMS ................................................................................. 702 15.5.2 Instrumentation for Atomic SIMS.................................................. 702 15.5.3 Molecular SIMS ............................................................................. 704 15.5.4 Polyatomic Primary Ion Beams...................................................... 705

15.6 Accelerator Mass Spectrometry............................................................. 707 15.7 Conclusion ............................................................................................. 710 References ..................................................................................................... 711

Appendix ............................................................................................................ 717 A.1 Units, Physical Quantities, and Physical Constants ................................ 717 A.2 Isotopic Composition of the Elements .................................................... 718 A.3 Carbon Isotopic Patterns......................................................................... 725 A.4 Chlorine and Bromine Isotopic Patterns ................................................. 726 A.5 Silicon and Sulfur Isotopic Patterns........................................................ 727 A.6 Isotopologs and Accurate Mass .............................................................. 727 A.7 Characteristic Ions .................................................................................. 728 A.8 Common Impurities ................................................................................ 729 A.9 Amino Acids........................................................................................... 730 A.10 Method Selection Guide ....................................................................... 731 A.11 How to Recognize Cationization .......................................................... 732 A.12 Systematic Approach to Mass Spectra.................................................. 733 A.13 Rules for the Interpretation of Mass Spectra......................................... 733 A.14 Nobel Prizes for Mass Spectrometry .................................................... 734

Subject Index ..................................................................................................... 735