Fast atom bombardment FAB and liquid secondary ion mass spectrometry LSIMS

3 Fast atom bombardment (FAB) and liquid secondary ion mass spectrometry (LSIMS) 

FAB and LSIMS ionise samples from a liquid matrix. They are applicable to involatile, high-molecular-weight and ionic species and therefore to most species of surfactant. For this reason a large part of this chapter is devoted to these techniques. Ionisation by FAB and LSIMS is soft. The spectra are dominated by molecular ions and quasimolecular ions. The high level of such ions allows identiflcation of species even from complex mixtures, for example whole-product formulations or environmental 

The matrix acts as a medium to promote ionisation (e.g. by cation attachment) and prolong the life of the sample. As material is lost from the matrix surface, diffusion of sample through the matrix allows a fresh supply of sample to be presented to the ionising beam. Commonly used matrices include glycerol, m-nitrobenzyl alcohol and thioglycerol. Anionic and cationic surfactants give intense spectra due to the presence of preformed ions in the matrix. Nonionic surfactants ionise by cation attachment. 

These sputtering techniques suffer from two main drawbacks, discrimination and irreproducibility. Highly surface-active species may dominate the spectra as a result of their suppression of other components of the sample at the surface of the matrix. This discrimination may result in poor sensitivity for certain species and makes quantitation difficult (see section 12.6.2). Ionisation of the matrix gives rise to chemical noise, and the spectra may be further complicated by the formation of sample-matrix adduct ions. These effects prevent the use of libraries in the interpretation of FAB and LSIMS spectra. 

Both FAB and LSIMS can be used in conjunction with continuous-flow inlet systems to optimise sensitivity, to improve reproducibility and to allow the use of in-line liquid chromatography for LC-MS. In the flow technique an LC pump delivers a continuous flow of solvent (containing a low concentration of the FAB/LSIMS matrix) to the point where the atom or ion beam is applied. The sample is introduced into this solvent flow by an LC injection valve and is delivered to the point of ionisation in a sharp concentrated slug. A good account of the method of continuous flow FAB is given in reference [5]. 

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Fast-atom bombardment (FAB) and liquid secondary-ion mass spectrometry (LSIMS) methods make up the category of the particle bombardment ionization. In both methods the analyte is dissolved in a liquid such as glycerol, thioglycerol, m-nitrobenzyl alcohol, or diethanolamine and about 1 1 is placed on a... 

Fast Atom Bombardment (FAB) and Liquid Secondary Ion Mass Spectrometry (LSIMS)... 

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