Ionization methods fast-atom bombardment

Some mild methods of ionization (e.g., chemical ionization. Cl fast-atom bombardment, FAB electrospray, ES) provide molecular or quasi-molecular ions with so little excess of energy that little or no fragmentation takes place. Thus, there are few, if any, normal fragment ions, and metastable ions are virtually nonexistent. Although these mild ionization techniques are ideal for yielding molecular mass information, they are almost useless for providing details of molecular structure, a decided disadvantage. 

Ionization methods that may be utihzed in LC-MS include electron ionization (El), chemical ionization (Cl), fast-atom bombardment (FAB), thermospray (TSP), electrospray (ESI) and atmospheric-pressure chemical ionization (APCI). 

Fig. 5 Statistical evaluation of LC-MS-based methods for tropane alkaloids referred in this chapter. (a) Relative frequency of ionization methods. +APCI positive atmospheric pressure chemical ionization, +ESI positive electrospray ionization, FAB fast atom bombardment, +TSP positive thermospray, (b) Relative frequency of scan modes used. MS full scan MS, MS/MS tandem mass spectrometry (product ion scan), MRM multiple reaction monitoring, SIM selected ion monitoring, (c) Relative frequency of mass analysers used. EBQtQ2 double focusing sector field mass spectrometer, IT ion trap, QqQ triple quadrupole, SQ single quadrupole. Considered publications were found by PubMed data-based search and references cited in these articles...

Early in the history of mass spectrometry (MS), large biomolecules were not analyzed because efficient methods to transport these molecules into the gas phase were unknown. Degradation typically occurred during vaporization of these nonvolatile molecules so that electron ionization of the intact molecular ion was not possible. Ionization by fast atom bombardment (FAB), field desorption (FD), secondary ionization mass spectrometry (SIMS), and plasma desorption (PD)" from the radioactive decay of Cf finally made the ionization and analysis of peptides possible. These latter techniques, although still used today, are not as popular as electrospray... 

El and Cl methods can be used if the compound to be studied is sufficiently volatile and stable to be vaporized intact. However, only 20% of the organics found in surface water are volatile enough to be amenable to GC-EI-MS or GC-CI-MS. Today, there are a variety of other ionization techniques available electrospray ionization (ESI), atmospheric pressure chemical ionization, matrix-assisted laser desorption ionization, and fast atom bombardment. Each of these has its advantages and disadvantages. A simple guideline to the most likely optimum ionization technique for a given class of substance is given in Table 1. 

After high quality mass spectra are obtained, the next step in data interpretation is to deduce the atomic composition of mass spectral features. Since mass spectra relate ion abundances with their mjz values, in order to find the molecular weight (m) of a compound, it is necessary to predict the charge state (z) of recorded ions. The number of electric charges acquired by ions in the gas phase is influenced by the ionization method. This problem used to be less important because old ionization techniques [e.g., electron ionization (El), chemical ionization (Cl), fast atom bombardment (EAB), secondary ion mass... 

Apart from the above methods of ionization, other notable methods are (i) atmospheric pressure chemical ionization, (ii) fast atom bombardment, (iii) chemiceil ionization emd (iv) inductively coupled plasma. 

See also Biochemical Applications of Mass Spectrometry Biomedical Applications of Atomic Spectroscopy Chromatography-MS, Methods Fast Atom Bombardment Ionization in Mass Spectrometry Isotopic Labelling in Mass Spectrometry. 

See also Chemical Structure Information from Mass Spectrometry Chromatography-MS, Methods Fast Atom Bombardment Ionization in Mass Spectrometry Fragmentation In Mass Spectrometry Hyphenated Techniques, Applications of in Mass Spectrometry Medical Applications of Mass Spectrometry MS-MS and MS Nucieic Acids and Nucieotides Studied Using Mass Spectrometry Peptides and Proteins Studied Using Mass Spectrometry Quadrupoies, Use of in Mass Spectrometry Sector Mass Spectrometers Surface induced Dissociation in Mass Spectrometry Time of Fiight Mass Spectrometers. 

The mass spectrometry section (Chapter 8) has been completely revised and expanded in this edition, starting with more detailed discussion of a mass spectrometer s components. All of the common ionization methods are covered, including chemical ionization (Cl), fast-atom bombardment (FAB), matrix-assisted laser desorption ionization (MALDl), and electrospray techniques. Different types of mass analyzers are desalbed as well. Fragmentation in mass spectrometry is discussed in greater detail, and several additional fiagmentation mechanisms for common functional groups are illustrated. Numerous new mass spectra examples are also included. 

Numerous ionization techniques have been reported in the last century, which are applicable to modern mass spectrometry. Depending on the method of analyte introduction (e.g., direct inlet, GC, LC, or capillary electrophoresis different strategies have been employed including El, Cl, thermospray, particle beam, electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), fast-atom bombardment (FAB), matrix-assisted laser desorption ionization (MALDI), etc. In sports drug testing, only selected approaches have been applied to routine doping control analyses, which are outlined in the following. 

A connnon feature of all mass spectrometers is the need to generate ions. Over the years a variety of ion sources have been developed. The physical chemistry and chemical physics communities have generally worked on gaseous and/or relatively volatile samples and thus have relied extensively on the two traditional ionization methods, electron ionization (El) and photoionization (PI). Other ionization sources, developed principally for analytical work, have recently started to be used in physical chemistry research. These include fast-atom bombardment (FAB), matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ES). 

FigureBl.7.2. Schematic representations of alternative ionization methods to El and PI (a) fast-atom bombardment in which a beam of keV atoms desorbs solute from a matrix (b) matrix-assisted laser desorption ionization and (c) electrospray ionization.

This method is still in use but is not described in this book because it has been superseded by more recent developments, such as particle beam and electrospray. These newer techniques have no moving parts, are quite robust, and can handle a wide variety of compound types. Chapters 8 through 13 describe these newer ionization techniques, including electrospray, atmospheric pressure ionization, plasmaspray, thermospray, dynamic fast-atom bombardment (FAB), and particle beam. 

Physical Chemical Characterization. Thiamine, its derivatives, and its degradation products have been fully characterized by spectroscopic methods (9,10). The ultraviolet spectmm of thiamine shows pH-dependent maxima (11). H, and nuclear magnetic resonance spectra show protonation occurs at the 1-nitrogen, and not the 4-amino position (12—14). The H spectmm in D2O shows no resonance for the thiazole 2-hydrogen, as this is acidic and readily exchanged via formation of the thiazole yUd (13) an important intermediate in the biochemical functions of thiamine. Recent work has revised the piC values for the two ionization reactions to 4.8 and 18 respectively (9,10,15). The mass spectmm of thiamine hydrochloride shows no molecular ion under standard electron impact ionization conditions, but fast atom bombardment and chemical ionization allow observation of both an intense peak for the patent cation and its major fragmentation ion, the pyrimidinylmethyl cation (16). 

One of the reasons for lack offlterature was probably because environmental analysis depends heavily on gas chromatography/mass spectrometry, which is not suitable for most dyes because of their lack of volatility (254). However, significant progress is being made in analyzing nonvolatile dyes by newer mass spectral methods such as fast atom bombardment (EAB), desorption chemical ionization, thermospray ionization, etc. 

Mass speetrometry has been used to eharaeterize mieroeystins using the method of fast-atom bombardment (FAB) ionization and MS/MS. Anatoxin-a has been analysed by MS in eombination with gas ehromatography in bloom and water samples, and in benthie eyanobaeterial material and stomaeh eontents of poisoned animals.Reeently, liquid ehromatography (LC) linked to MS has been employed to analyse mieroeystins, where FAB-MS and atmospherie-pressiire ionization (API-MS) have been used, and anatoxin-a, where thermospray (TSP-MS) was iised. ... 

Fast-atom bombardment An ionization method used for involatile and thermally labile materials. In this technique, the sample is dissolved in a matrix material and bombarded with a high-energy atom or ion beam. 

Mass spectrometry (MS) in its various forms, and with various procedures for vaporization and ionization, contributes to the identification and characterization of complex species by their isotopomer pattern of the intact ions (usually cation) and by their fragmentation pattern. Upon ionization by the rough electron impact (El) the molecular peak often does not appear, in contrast to the more gentle field desorption (FD) or fast-atom bombardment (FAB) techniques. An even more gentle way is provided by the electrospray (ES) method, which allows all ionic species (optionally cationic or anionic) present in solution to be detected. Descriptions of ESMS and its application to selected problems are published 45-47 also a representative application of this method in a study of phosphine-mercury complexes in solution is reported.48... 

Volatile or volatilizable compounds may be introduced into the spectrometer via a pinhole aperture or molecular leak which allows a steady stream of sample molecules into the ionization area. Non-volatile or thermally labile samples are introduced directly by means of an electrically heated probe inserted through a vacuum lock. Numerous methods of sample ionization are available of which the most important are electron impact (El), chemical ionization (CY), field ionization (FI), field desorption (FD), fast atom bombardment (FAB), and radio-frequency spark discharge. 

Fast atom bombardment FAB Particle induced desorption/ ionization Nonvolatile molecular ions Soft method Large molecules... 

Mass spectrometry is traditionally a gas phase technique for the analysis of relatively volatile samples. Effluents from gas chromatographs are already in a suitable form and other readily vaporized samples could be fairly easily accommodated. However the coupling of mass spectrometry to liquid streams, e.g. HPLC and capillary electrophoresis, posed a new problem and several different methods are now in use. These include the spray methods mentioned below and bombarding with atoms (fast atom bombardment, FAB) or ions (secondary-ion mass spectrometry, SIMS). The part of the instrument in which ionization of the neutral molecules occurs is called the ion source. The commonest method of... 

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