Jiirgen H. Gross Mass Spectrometry
J urgen H. Gross Mass Spectrometry A Textbook With 357 Illustrations and Tables ~ Springer
DR. JURGEN H. GROSS Institute of Organic Chemistry University of Heidelberg 1m Neuenheimer Feld 270 69120 Heidelberg Germany author@ms-textbook.com Problems and Solutions available via author's website www.ms-textbook.com Library of Congress Control Number: 2006923046 1st ed. 2004. Corr. 2nd printing ISBN 978-3-642-07388-5 DOl 10.1007/978-3-540-36756-7 ISBN 978-3-540-36756-7 (ebook) This work is subject to copyright. All rights reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable for prosecution under the German Copyright Law. Springer is a part of Springer Science+Business Media springer. com Springer-Verlag Berlin Heidelberg 2004 Softcover reprint of the hardcover 1st edition 2004 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Typesetting: Data conversion by author Production: LE-Tpc, Jelonek, Schmidt & V6ckler GbR, Leipzig Coverdesign: KiinkelLopka, Heidelberg Printed on acid-free paper 2/3100NL - 5 4 3 2 1 0
Dedicated to my wife Michaela and my daughters Julia and Elena
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 Imagination. 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 University 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. Having completed my doctoral thesis on fragmentation pathways of isolated immonium 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, remarks, and comments were essential. Therefore, P. Enders, Springer-Verlag Heidelberg (Introduction), J. Grotemeyer, University of Kiel (Gas Phase Ion Chemistry), S. Giesa, Bayer Industry Services, Leverkusen (Isotopes), 1. Franzen, Bruker
VIII 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 NISTIEPAINIH 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 official 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 contribute 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 many facets of mass spectrometry and will satisfy your expectations. Jtirgen H. Gross University of Heidelberg Institute of Organic Chemistry 1m Neuenheimer Feld 270 69120 Heidelberg Germany email: author@ms-textbook.com
Table of Contents Contents... IX 1 Introduction... 1 1.1 Aims and Scope... 1 l.2 What Is Mass Spectrometry?... 2 1.2.1 Mass Spectrometry... 3 1.2.2 Mass Spectrometer... 3 1.2.3 Mass Spectrum... 4 1.3 Filling the Black Box... 7 1.4 Terminology... 7 1.5 Units, Physical Quantities, and Physical Constants... 9 Reference List... 10 2 Gas Phase Ion Chemistry... 13 2.1 Quasi-Equilibrium Theory... l3 2.1.1 Basic Assumptions of QET... 14 2.2 Ionization... 14 2.2.1 Electron Ionization... 15 2.2.2 Ionization Energy... 16 2.3 Vertical Transitions... 18 2.4 Ionization Efficiency and Ionization Cross Section... 20 2.5 Internal Energy and the Further Fate oflons... 21 2.5.1 Degrees of Freedom... 21 2.5.2 Appearance Energy... 22 2.5.3 Bond Dissociation Energies and Heats offormation... 24 2.5.4 Randomization of Energy... 26 2.6 Rate Constants from QET... 27 2.6.1 Meaning of the Rate Constant... 28 2.6.2 Typical k(e) Functions... 29 2.6.3 Description of Reacting Ions Using k(e) Functions... 29 2.6.4 Direct Cleavages and Rearrangement Fragmentations... 30 2.6.5 Practical Consequences ofinternal Energy... 31
X Table of Contents 2.7 Time Scale of Events... 32 2.7.1 Stable, Metastable, and Unstable Ions... 33 2.7.2 Kinetic Shift... 35 2.8 Activation Energy of the Reverse Reaction and Kinetic Energy Release.. 36 2.8.1 Activation Energy ofthe Reverse Reaction... 36 2.8.2 Kinetic Energy Release... 37 2.9 Isotope Effects... 40 2.9.1 Kinetic Isotope Effects... 40 2.10 Determination oflonization Energies and Appearance Energies....44 2.10.1 Conventional Determination of Ionization Energies... 44 2.10.2 Experimental Improvements of IE Accuracy....45 2.10.3 Photoelectron Spectroscopy and Derived Modem Methods... 46 2.10.4 Determination of Appearance Energies... 48 2.10.5 Breakdown Graphs... 49 2.11 Gas Phase Basicity and Proton Affinity... 50 2.12 Tandem Mass Spectrometry... 53 2.12.1 Collision-Induced Dissociation... 53 2.12.2 Other Methods of Ion Activation... 57 2.12.3 Reactive Collisions... 59 Reference List... 61 3 Isotopes... 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 Calculation of Atomic, Molecular, and Ionic Mass... 71 3.1.5 Natural Variations in Relative Atomic Mass... 73 3.2 Calculation ofisotopic Distributions... 74 3.2.1 X+l Element Carbon... 74 3.2.2 Binomial Approach... 77 3.2.3 Halogens... 78 3.2.4 Combinations of Carbon and Halogens... 79 3.2.5 Polynomial Approach... 80 3.2.6 Oxygen, Silicon and Sulfur... 81 3.2.7 Polyisotopic Elements... 83 3.2.8 Practical Aspects of Isotopic Patterns... 84 3.2.9 Isotopic Enrichment and Isotopic Labeling... 87 3.3 High-Resolution and Accurate Mass... 88 3.3.1 Exact Mass... 88 3.3.2 Deviations from Nominal Mass... 89 3.3.3 Mass Accuracy... 92 3.3.4 Resolution... 96 3.3.5 Mass Calibration... 99 3.4 Interaction of Resolution and Isotopic Patterns... 104 3.4.1 Multiple Isotopic Compositions at Very High Resolution... 104
XI 3.4.2 Multiple Isotopic Compositions and Accurate Mass... 106 3.4.3 Isotopic Patterns of Large Molecules... 106 3.5 Interaction of Charge State and Isotopic Patterns... 108 Reference List... 109 4 Instrumentation... 111 4.1 Creating a Beam of Ions... 112 4.2 Time-of-Flight Instruments... 113 4.2.1 Introduction to Time-of-Flight... 113 4.2.2 Basic Principle of TOF Instruments... 114 4.2.3 Linear Time-of-Flight Analyzer... 117 4.2.4 Reflector Time-of-Flight Analyzer.... 119 4.2.5 Further Improvement of Resolution... 122 4.2.6 Orthogonal Acceleration TOF... 125 4.2.7 Tandem MS on TOF Instruments... 128 4.3 Magnetic Sector Instruments... 130 4.3.1 Introduction to Magnetic Sector Instruments... 130 4.3.2 Principle of the Magnetic Sector... 131 4.3.3 Double-Focusing Sector Instruments... 134 4.3.4 Setting the Resolution of a Sector Instrument..... 138 4.3.5 Further Improvement of Sector Instruments... 139 4.3.6 Tandem MS with Magnetic Sector Instruments... 140 4.4 Linear Quadrupole Instruments... 145 4.4.1 Introduction to the Linear Quadrupole... 145 4.4.2 Principle of the Linear Quadrupole... 146 4.4.3 Resolving Power of Linear Quadrupoles... 150 4.4.4 RF-Only Quadrupoles... 151 4.4.5 Tandem MS with Quadrupole Analyzers... 152 4.4.6 Linear Quadrupole Ion Traps... 153 4.5 Three-Dimensional Quadrupole Ion Trap... 15 4 4.5.1 Introduction to the Quadrupole Ion Trap... 154 4.5.2 Principle of the Quadrupole Ion Trap... 155 4.5.3 Operation of the Quadrupole Ion Trap... 157 4.5.4 External Ion Sources for the Quadrupole Ion Trap... 162 4.5.6 Tandem MS with the Quadrupole Ion Trap... 163 4.6 Fourier Transform Ion Cyclotron Resonance... 164 4.6.1 Introduction to Ion Cyclotron Resonance... 164 4.6.2 Principle of Ion Cyclotron Resonance... 165 4.6.3 Fourier Transform Ion Cyclotron Resonance... 166 4.6.4 Experimental Setup offt-icr-ms... 167 4.6.5 Excitation Modes in FT-ICR-MS... 168 4.6.6 Detection in FT-ICR-MS... 169 4.6.7 External Ion Sources for FT-ICR-MS... 171 4.6.8 Tandem MS with FT-ICR Instruments... 172 4.7 Hybrid Instruments... 173 4.8 Detectors... 175
XII Table of Contents 4.8.1 Discrete Dynode Electron Multipliers... 175 4.8.2 Channel Electron Multipliers... 176 4.8.3 Microchannel Plates... 177 4.8.4 Post-Acceleration and Conversion Dynode... 178 4.8.5 Focal Plane Detectors... 179 4.9 Vacuum Technology... 180 4.9.1 Basic Mass Spectrometer Vacuum System... 180 4.9.2 High Vacuum Pumps... 181 4.10 Buying an Instrument... 182 Reference List.... 182 5 Electron Ionization... 193 5.1 Behavior of Neutrals Upon Electron Impact... 193 5.1.1 Formation of Ions... 193 5.1.2 Processes Accompanying Electron Ionization... 195 5.1.3 Efficiency of Electron Ionization... 196 5.1.4 Practical Consequences of Internal Energy... 197 5.1.5 Low-Energy Electron Ionization Mass Spectra... 198 5.2 Electron Ionization Ion Sources... 200 5.2.1 Layout of an Electron Ionization Ion Source... 200 5.2.2 Generation of Primary Electrons... 202 5.2.3 Overall Efficiency of an Electron Ionization Ion Source... 203 5.2.4 Optimization of Ion Beam Geometry... 205 5.3 Sample Introduction... 206 5.3.1 Direct Insertion Probe... 206 5.3.2 Direct Exposure Probe... 210 5.3.3 Reference Inlet System... 211 5.3.4 Gas Chromatograph... 213 5.3.5 Liquid Chromatograph... 213 5.4 Ion Chromatograms... 214 5.4.1 Total Ion Current... 214 5.4.2 Reconstructed Ion Chromatogram... 215 5.5 Mass Analyzers for EI... 217 5.6 Analytes for EI.... 217 5.7 Mass Spectral Databases for EI... 218 Reference List... 218 6 Fragmentation of Organic Ions and Interpretation of EI Mass Spectra '" 223 6.1 Cleavage of a Sigma-Bond... 223 6.1.1 Writing Conventions for Molecular Ions... 223 6.1.2 a-bond Cleavage in Small Non-Functionalized Molecules... 225 6.1.3 'Even-Electron Rule'... 226 6.1.4 a-bond Cleavage in Small Functionalized Molecules... 228 6.2 Alpha-Cleavage... 229 6.2.1 a-cleavage of Acetone Molecular Ion... 229 6.2.2 Stevenson's Rule... 230
XIII 6.2.3 a-cleavage of Non-Symmetrical Aliphatic Ketones... 232 6.2.4 Acylium Ions and Carbenium Ions... 234 6.2.5 a-cleavage of Amines, Ethers, and Alcohols... 235 6.2.6 a-cleavage of Halogenated Hydrocarbons... 243 6.2.7 Double a-cleavage... 244 6.3 Distonic Ions... 247 6.3.1 Definition of Distonic Ions... 247 6.3.2 Formation and Properties of Distonic Ions... 247 6.3.3 Distonic Ions as Intermediates... 248 6.4 Benzylic Bond Cleavage... 249 6.4.1 Cleavage of the Benzylic Bond in Phenyl alkanes... 249 6.4.2 The Further Fate of [C6Hst and [C 7H 7t... 251 6.4.3 Isomerization of [C7Hst' and [CsHsr'Ions... 252 6.4.4 Rings Plus Double Bonds... 254 6.5 Allylic Bond Cleavage... 255 6.5.1 Cleavage of the Allylic Bond in Aliphatic Alkenes... 255 6.5.2 Methods for the Localization of the Double Bond... 257 6.6. Cleavage of Non-Activated Bonds... 258 6.6.1 Saturated Hydrocarbons... 258 6.6.2 Carbenium Ions... 260 6.6.3 Very Large Hydrocarbons... 262 6.6.4 Recognition of the Molecular Ion Peak... 263 6.7 McLafferty Rearrangement...... 264 6.7.1 McLafferty Rearrangement of Aldehydes and Ketones... 264 6.7.2 Fragmentation of Carboxylic Acids and Their Derivatives... 267 6.7.3 McLafferty Rearrangement of Aromatic Hydrocarbons... 271 6.7.4 McLafferty Rearrangement with Double Hydrogen Transfer... 272 6.8 Retro-Diels-Alder Reaction... 276 6.8.1 Properties of the Retro-Diels-Alder Reaction... 276 6.8.2 Influence of Positional Isomerism on the RDA Reaction... 278 6.8.3 Is the RDA Reaction Stepwise or Concerted?... 279 6.8.4 RDA Reaction in Natural Products... 279 6.8.5 Widespread Occurrence of the RDA Reaction... 280 6.9 Elimination of Carbon Monoxide... 281 6.9.1 CO Loss from Phenols... 281 6.9.2 CO and C 2H 2 Loss from Quinones... 283 6.9.3 Fragmentation of Arylalkylethers... 285 6.9.4 CO Loss from Transition Metal Carbonyl Complexes... 287 6.9.5 CO Loss from Carbonyl Compounds... 288 6.9.6 Differentiation Between Loss of CO, N20 and C2H4........ 288 6.10 Thermal Degradation Versus Ion Fragmentation... 289 6.10.1 Decarbonylation and Decarboxylation... 289 6.10.2 Retro-Diels-Alder Reaction... 289 6.10.3 Loss of H 20 from Alkanols... 290 6.10.4 EI Mass Spectra of Organic Salts... 291 6.11 Alkene Loss from Onium Ions... 292
XIV Table of Contents 6.11.1 McLafferty Rearrangement of Onium Ions... 293 6.11.2 Onium Reaction... 296 6.12 Ion-Neutral Complexes... 300 6.13 Ortha Elimination (Ortha Effect)... 304 6.13.1 Ortha Elimination from Molecular Ions... 305 6.13.2 Ortha Elimination from Even-Electron Ions... 306 6.13.3 Ortha Elimination in the Fragmentation of Nitroarenes... 308 6.14 Heterocyclic Compounds... 311 6.14.1 Saturated Heterocyclic Compounds... 311 6.14.2 Aromatic Heterocyclic Compounds... 315 6.15 Guidelines for the Interpretation of Mass Spectra... 319 6.15.1 Summary of Rules... 319 6.15.2 Systematic Approach to Mass Spectra... 320 Reference List..... 320 7 Chemical Ionization... 331 7.1 Basics of Chemical Ionization... 331 7.1.1 Formation oflons in Chemical Ionization... 331 7.1.2 Chemical Ionization Ion Sources... 332 7.1.3 Sensitivity of Chemical Ionization... 333 7.2 Chemical Ionization by Protonation... 333 7.2.1 Source of Protons... 333 7.2.2 Methane Reagent Gas Plasma... 334 7.2.3 Energetics of Protonation... 336 7.2.4 Methane Reagent Gas PICI Spectra... 337 7.2.5 Other Reagent Gases in PICI... 338 7.3 Charge Exchange Chemical Ionization... 341 7.3.1 Energetics of CE... 341 7.3.2 Reagent Gases for CE-CI... 342 7.3.4 Compound Class-Selective CE-CI... 343 7.3.5 Regio- and Stereoselectivity in CE-CI... 344 7.4 Electron Capture... 345 7.4.1 Ion Formation by Electron Capture... 345 7.4.3 Energetics ofec... 345 7.4.4 Creating Thermal Electrons... 347 7.4.5 Appearance of EC Spectra... 348 7.4.6 Applications of EC... 348 7.5 Sample Introduction in CI... 348 7.5.1 Desorption Chemical Ionization... 349 7.6 Analytes for CI... 350 7.7 Mass Analyzers for CI... 351 Reference List... 351 8 Field Ionization and Field Desorption... 355 8.1 Field Ionization Process... 355 8.2 PI and FD Ion Source... 357
xv 8.3 Field Emitters... 358 8.3.1 Blank Metal Wires as Emitters... 358 8.3.2 Activated Emitters... 358 8.3.3 Emitter Temperature... 359 8.3.4 Handling of Activated Emitters... 360 8.3.5 Liquid Injection Field Desorption Ionization... 362 8.4 FI Spectra... 363 8.4.1 Origin of [M+Ht Ions in FI-MS... 363 8.4.2 Field-Induced Dissociation... 364 8.4.3 Multiply-Charged Ions in FI-MS... 364 8.5 FD Spectra... 365 8.5.1 Ion Formation in FD-MS... 365 8.5.2 Cluster Ion Formation in FD-MS... 369 8.5.3 FD-MS of Ionic Analytes... 371 8.5.4 Best Anode Temperature and Thennal Decomposition... 372 8.5.5 FD-MS of Polymers... 373 8.5.6 Sensitivity of FI-MS and FD-MS... 373 8.5.7 Types of Ions in FD-MS... 374 8.6 Analytes for FI and FD... 375 8.7 Mass Analyzers for FI and FD... 376 Reference List... 376 9 Fast Atom Bombardment... 381 9.1 Ion Sources for F AB and LSIMS... 382 9.1.1 FAB Ion Sources... 382 9.1.2 LSIMS Ion Sources... 383 9.1.3 FAB Probes... 383 9.2 Ion Formation in FAB and LSIMS... 384 9.2.1 Ion Formation from Inorganic Samples... 384 9.2.2 Ion Formation from Organic Samples... 385 9.3 FAB Matrices... 387 9.3.1 The Role of the Liquid Matrix... 387 9.3.2 Characteristics of FAB Matrix Spectra... 388 9.3.3 Unwanted Reactions in FAB-MS... 389 9.4 Applications offab-ms... 389 9.4.1 FAB-MS of Analytes of Low to Medium Polarity... 389 9.4.2 FAB-MS oflonic Analytes... 391 9.4.3 High-Mass Analytes in FAB-MS... 392 9.4.4 Accurate Mass Measurements in FAB... 393 9.4.5 Continuous-Flow FAB... 395 9.4.6 Low-Temperature FAB... 396 9.4.7 FAB-MS and Peptide Sequencing... 398 9.5 Massive Cluster Impact....400 9.6 252Califomium Plasma Desorption... 400 9.7 General Characteristics of FAB and LSIMS....402 9.7.1 Sensitivity offab-ms... 402
XVI Table of Contents 9.7.2 Types of Ions in FAB-MS... 402 9.7.3 Analytes for FAB-MS... 403 9.7.4 Mass Analyzers for FAB-MS... 403 Reference List.... 404 10 Matrix-Assisted Laser Desorption/Ionization... 411 10.1 Ion Sources for LOI and MALOI... 411 10.2 Ion Formation... 413 10.2.1 Ion Yield and Laser Fluence....413 10.2.2 Effect of Laser Irradiation on the Surface... 414 10.2.3 Temporal Evolution of a Laser Oesorption Plume....415 10.2.4 Ion Formation in MALDI... 416 10.3 MALOI Matrices... 416 10.3.1 Role of the Solid Matrix... 416 10.3.2 Matrices in UV-MALOI...... 417 10.3.3 Characteristics ofmaldi Matrix Spectra....418 10.4 Sample Preparation... 419 10.4.1 Standard Sample Preparation....419 10.4.2 Cationization and Cation RemovaL....420 10.4.3 Solvent-Free Sample Preparation... 421 10.4.4 Sample Introduction... 422 10.4.5 Additional Methods of Sample Supply....423 10.4 Applications of LDI... 423 10.5 Applications of MALDI... 425 10.5.1 MALDI-MS of Synthetic Polymers....425 10.5.2 Fingerprints by MALDI-MS... 427 10.5.3 Carbohydrates by MALDI-MS....427 10.5.4 Structure Elucidation of Carbohydrates by MALDI... 428 10.5.5 Oligonucleotides in MALDI... 429 10.6 Oesorption/lonization on Silicon... 430 10.7 Atmospheric Pressure MALOI... 431 10.8 General Characteristics of MALOI...... 432 10.8.1 Sample Consumption and Oetection Limit... 432 10.8.2 Analytes for MALOI..... 432 10.8.3 Types of Ions in LDI and MALDI-MS... 433 10.8.4 Mass Analyzers for MALDI-MS... 433 Reference List.... 434 11 Electrospray Ionization... 441 11.1 Oevelopment of ESI and Related Methods... 441 11.1.1 Atmospheric Pressure Ionization... 441 11.1.2 Thermospray... 442 11.1.3 Electrohydrodynarnic Ionization... 443 11.1.4 Electrospray Ionization... 444 11.2 Ion Sources for ESI.... 444 11.2.1 Basic Oesign Considerations... 444
XVII 11.2.2 ESI with Modified Sprayers... 445 11.2.3 Nano-Electrospray... 447 11.2.4 ESI with Modified Spray Geometries... 449 11.2.5 Skimmer CID... 451 11.3 Ion Formation... 451 11.3.1 Formation of an Electrospray....451 11.3.2 Disintegration of Charged Droplets... 453 11.3.3 Formation of Ions from Charged Droplets....454 11.4 Charge Deconvolution....455 11.4.1 Problem of Multiple Charging....455 11.4.2 Mathematical Charge Deconvolution....458 11.4.3 Hardware Charge Deconvolution....460 11.4.4 Controlled Charge Reduction in ESI......461 11.5 Applications of ESI...... 462 11.5.1 ESI of Small Molecules....462 11.5.2 ESI of Metal Complexes... 462 11.5.3 ESI of Surfactants....464 11.5.4 Oligonucleotides, DNA, and RNA....464 11.5.5 ESI of Oligosaccharides....465 11.6 Atmospheric Pressure Chemical Ionization....465 11.7 Atmospheric Pressure Photoionization....467 11.8 General Characteristics of ESI..... 467 11.8.1 Sample Consumption... 467 11.8.2 Types of Ions in ESI......468 11.8.3 Mass Analyzers for ESI......468 Reference List... 468 12 Hyphenated Methods... 475 12.1 General Properties of Chromatography-Mass Spectrometry Coupling..475 12.1.1 Chromatograms and Spectra... 477 12.1.2 Selected Ion Monitoring... 478 12.1.3 Quantitation... 479 12.2 Gas Chromatography-Mass Spectrometry... 482 12.2.1 GC-MS Interfaces... 482 12.2.2 Volatility and Derivatization....483 12.2.3 Column Bleed... 483 12.2.4 Fast GC-MS... 484 12.3 Liquid Chromatography-Mass Spectrometry....485 12.3.1 LC-MS Interfaces... 485 12.3.2 Multiplexed Electrospray Inlet Systems....487 12.3 Tandem Mass Spectrometry....488 12.4. Ultrahigh-Resolution Mass Spectrometry... 490 Reference List... 491
XVIII Table of Contents Appendix... 495 1 Isotopic Composition of the Elements....495 2 Carbon Isotopic Patterns... 50 1 3 Silicon and Sulfur Isotopic Patterns... 502 4 Chlorine and Bromine Isotopic Patterns... 503 5 Characteristic Ions... 503 6 Frequent Impurities... 505 Subject Index... 507