Fast atom bombardment methods

Mass spectrometry is a valuble tool with which an abundancy of structural information may be obtained from a minute amount of material. Capillary electrophoresis may be interfaced with mass spectrometry by electrospray ionization [124-126] or continuous-flow, fast-atom bombardment methods [127,128]. Several reviews discuss applications of the interfacing techniques, and address the attributes and disadvantages associated with these methods [129,130]. Critical parameters involved in the optimization of CE-electrospray ionization mass spectrometry analysis have been reviewed as well [131],... 

J. R. Chapman. Analysis of glycoproteins and glycopeptides using fast-atom bombardment. Methods in Molecular Biology 1997, 61, 161-253. 

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.

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. 

This method is still in use but is not described in this book because it has been superseded by more recent developments, such as particle beam and electrospray.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. ... 

The mass spectrometry of diazo compounds was reviewed by Zeller (1983) and by Lebedev (1991). It is difficult to record mass spectra of diazonium salts using conventional techniques. With the water thermospray method, however, Schmelzeisen-Redeker et al. (1985) observed the diazonium ion and various fragments such as [Ar+ - N2 + 2H]+ and [Ar + N2 + H20]+. Ambroz et al. (1988) applied the fast atom bombardment (FAB) technique using a 3-nitrobenzylalcohol matrix. Peaks for ArNJ, Ar+, and [M + ArN2]+ and further peaks due to solvated ions were found. 

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). 

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. 

Whereas the use of conventional fast atom bombardment (FAB) in the analysis of polymer/additive extracts has been reported (see Section 6.2.4), the need for a glycerol (or other polar) matrix might render FAB-MS analysis of a dissolved polymer/additive system rather unattractive (high chemical background, high level of matrix-, solvent- and polymer-related ions, complicated spectra). Yet, in selected cases the method has proved quite successful. Lay and Miller [53] have developed an alternative method to the use of sample extraction, cleanup, followed by GC in the quantitative analysis of PVC/DEHP with plasticiser levels as typically found in consumer products (ca. 30 %). The method relied on addition of the internal standard didecylphthalate (DDP) to a THF solution of the PVC sample with FAB-MS quantitation based on the relative signal levels of the [MH]+ ions of DEHP and DDP obtained from full-scan spectra, and on the use of a calibration curve (intensity ratio m/z 391/447 vs. mg DEHP/mg DDP). No FAB-matrix was added. No ions associated with the bulk of the PVC polymer were observed. It was... 

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... 

S. Beranova-Giorgianni and D. M. Desiderio. Fast Atom Bombardment Mass Spectrometry of Synthetic Peptides. In Methods in Enzymology Solid-Phase Peptide Synthesis, ed. G. B. Fields. Methods in Enzymology 289. Academic Press, San Diego, 1997, 478-499. 

R. M. Caprioli and W. T. Moore. Continuous-Flow Fast Atom Bombardment Mass Spectrometry. In Methods in Enzymology Mass Spectrometry, ed. J. A. McCloskey. Methods in Enzymology 193, Academic Press, San Diego, 1990, 214-237. 

While fast atom bombardment (FAB) [66] and TSI [25] built up the basis for a substance-specific analysis of the low-volatile surfactants within the late 1980s and early 1990s, these techniques nowadays have been replaced successfully by the API methods [22], ESI and APCI, and matrix assisted laser desorption ionisation (MALDI). In the analyses of anionic surfactants, the negative ionisation mode can be applied in FIA-MS and LC-MS providing a more selective determination for these types of compounds than other analytical approaches. Application of positive ionisation to anionics of ethoxylate type compounds led to the abstraction of the anionic moiety in the molecule while the alkyl or alkylaryl ethoxylate moiety is ionised in the form of AE or APEO ions. Identification of most anionic surfactants by MS-MS was observed to be more complicated than the identification of non-ionic surfactants. Product ion spectra often suffer from a reduced number of negative product ions and, in addition, product ions that are observed are less characteristic than positively generated product ions of non-ionics. The most important obstacle in the identification and quantification of surfactants and their metabolites, however, is the lack of commercially available standards. The problems with identification will be aggravated by an absence of universally applicable product ion libraries. 

Numerous chromatographic methods coupled with MS have been developed for quaternary ammonium compounds. HPLC and fast atom bombardment mass spectrometry (FAB-MS) techniques have been applied to analyse concentrations of alkyldimethylbenzyl ammonium... 

Early work by Rivera et al. [27] indicated that GAC filters installed at the waterworks Llobregat were capable of retaining different polar pollutants including LAS, NPEO and PEG, but most of them reached (to an unknown portion as the applied fast atom bombardment (FAB)-MS method only yielded qualitative results) the drinking water. Hence, further examinations covering at least one GAC cycle should be performed to obtain more information on the efficacy of GAC filtration... 

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