Fast atom bombardment-mass spectrometry instrumentation

The FABMS (Fast Atom Bombardment Mass Spectrometry) technique Is reviewed In this chapter with emphasis upon laboratory Instrumentation and procedures. 

NMR spectra were recorded on a Briiker AM 300 instrument. IR spectra were recorded on a Perkin Elmer 1710 IR FT spectrometer. UV spectra were recorded on a Perkin-Elmer Lambda 6 spectrometer. Electrochemical measurements were conducted on a Princeton Applied Research Potentiostat/Galvanostat Model 273. Fast atom bombardment mass spectra were performed at University College, Swansea by the S.E.R.C. mass spectrometry service. All elemental analyses were carried out by the Inorganic Chemistry Laboratory, Oxford. 

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... 

General. NMR spectra were obtained on a Bruker WM-250 instrument with tetramethylsilane (TMS) as internal standard. UV-visible spectra were taken on a Varian Cary 219. Fast-atom bombardment (FAB) mass spectrometry (MS) analysis were completed on a Vacuum Generators ZAB-2F double-focusing or a Varian MAT CH5 mass spectrometer equipped with an Ion Tech FAB Gun. Solvents for FAB matrix were made up of thioglycerol, dithiothreitol, and dithioerythretol (2 1 1) addition of 0.1M trifluoroacetic acid to the matrix facilitated the ionization of the porphyrins during FAB analysis.(13)... 

Over 30 years of liquid chromatography-mass spectrometry (LC-MS) research has resulted in a considerable number of different interfaces (Ch. 3.2). A variety of LC-MS interfaces have been proposed and built in the various research laboratories, and some of them have been adapted by instmment manufacturers and became commercially available. With the advent in the early 1990 s of interfaces based on atmospheric-pressure ionization (API), most of these interfaces have become obsolete. However, in order to appreciate LC-MS, one carmot simply ignore these earlier developments. This chapter is devoted to the older LC-MS interfaces, which is certainly important in understanding the histoiy and development of LC-MS. Attention is paid to principles, instrumentation, and application of the capillary inlet, pneumatic vacuum nebulizers, the moving-belt interface, direct liquid introduction, continuous-flow fast-atom bombardment interfaces, thermospray, and the particle-beam interface. More elaborate discussions on these interfaces can be found in previous editions of this book. 

Mass spectrometry currently has assumed a central role in protein sequencing. This development has been possible with the introduction of two highly sensitive ionization techniques electrospray ionization (ESI) and matrix-assisted laser desorption and ionization (MALDI) and the advent of improved instrumentation capable of high-mass and high-sensitivity detection. Currently, biopolymers with a molecular mass over 100,000 Da are analyzed routinely. In the past, fast atom bombardment (FAB) [6,7] and Cf plasma desorption (PD) ionization [8] also played a limited role in protein sequencing. Mass spectrometry now has assumed... 

Hyphenated TLC techniques. TLC has been coupled with other instrumental techniques to aid in the detection, qualitative identification and, occasionally, quantitation of separated samples, and these include the coupling of TLC with high-pressure liquid chromatography (HPLC/TLC), with Fourier transform infra-red (TLC/FTIR), with mass spectrometry (TLC/ MS), with nuclear magnetic resonance (TLC/NMR) and with Raman spectroscopy (TLC/RS). These techniques have been extensively reviewed by Busch (1996) and by Somsen, Morden and Wilson (1995). The chemistry of oils and fats and their TLC separation has been so well established that they seldom necessitate the use of these coupling techniques for their identification, although these techniques have been used for phospholipid detection. Kushi and Handa (1985) have used TLC in combination with secondary ion mass spectrometry for the analysis of lipids. Fast atom bombardment (FAB) has been used to detect the molecular species of phosphatidylcholine on silica based on the molecular ion obtained by mass spectrometry (Busch et al, 1990). 

Similar to any mass spectrometric experiment, ions that are intended to be converted to neutrals in NR MS should be first generated by appropriate ionization methods. In principle, all ionization methods described in Chapter 2.28 may be used for the generation of ions for NR MS studies. However, only a limited number of ionization techniques have found practical use for this purpose. They are electron impact, chemical ionization, fast atom bombardment, and secondary ion mass spectrometry. One of the reasons for not using other methods is that NR MS experiments are mostly carried out on sector instruments. The mass spectrometers of this type are usually equipped with relatively old methods of ionization. The second reason for using these methods is that they provide high ion fluxes of ions of interest. This condition is crucial for many NR MS experiments because of the overall low total efficiency (<0.1%) of the neutralization-reionization process. 

Several mass spectrometric techniques including fast atom bombardment (FAB), plasma desorption (PD), matrix-assisted laser desorption/ionization (MALDI), and electrospray (ES) mass spectrometry (MS) are presently available for the analysis of peptides and proteins (Roepstorff and Richter, 1992). Of these techniques, mainly PDMS has gained footing in protein laboratories because the instrumentation is relatively cheap and simple to operate and because, taking advantage of a nitrocellulose matrix, it is compatible with most procedures in protein chemistry (Cotter, 1988 Roepstorff, 1989). Provided that the proper care is taken in the sample preparation procedure most peptides and small proteins (up to 10 kDa) are on a routine basis amenable to analysis by PDMS. Molecular mass information can be obtained with an accuracy of 0.1% or better. Structural information can be gained by application of successive biochemical or chemical procedures to the sample. 

Mass Spectrometry (MS). MS is one of the key techniques used in structure determination of carbohydrates and analyses via electron impact (E.I.) and chemical ionization (C.I.) methods are performed routinely on low molecular weight permethylated or peracetylated carbohydrates. Recently, MS procedures have found wider application in the structure elucidation of less volatile higher molecular weight oligosaccharides as a result of instrumental developments (in particular, desorption methods of ionization, based on fast atom bombardment (FAB) (93), field desorption (FD), laser desorption (LD), plasma desorption (PD), and secondary ion (SI) mass spectrometry) and improvements in derivatization techniques. For example, a series of malto-oligosaccharides, starch and other glycans have been examined with LD FD-MS (94,95) whilst FAB techniques have been employed for studies of cello- and malto-oligosaccharides (96) and branched cyclo-dextrins (97). 

Fast atom bombardment (FAB) mass spectrometry was developed in the 1980s and has a number of advantages over FI molecular masses up to 10 000 can be determined, the instrument can be run in both positive and negative modes permitting both positive and negative ions to be... 

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