Matrix materials fast-atom bombardment

Fast-atom bombardment (FAB) is one of a number of ionization techniques which utilize a matrix material, in which the analyte is dissolved, to transfer sufficient energy to the analyte to facilitate ionization. In FAB, the matrix material is a liquid, such as glycerol, and the energy for ionization is provided by a high-energy atom (usually xenon) or, more recently, an ion (Cs+) beam. In conventional FAB, the solution of analyte in the matrix material is applied to the end of a probe which is placed in the source of the mass spectrometer where it is bombarded with the atom/ion beam. 

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. 

Matrix material A material used in fast-atom bombardment and matrix-assisted laser desorption ionization to transfer energy to an analyte molecule to bring about its ionization. 

With the introduction of fast-atom bombardment (FAB) in 1982, and matrix-assisted laser desorption/ ionization (MALDI) and electrospray ionization (ESI), most of the biomedical applications have been directed towards these methods. The 52( f.pD method has been found to have wide applicability, including the study of refractory materials, catalysts, semiconductors and frozen gases. Electronics capable of measuring the timing of events with subnanosecond resolution (the time it takes for a single photon to travel 1 cm) is used by this method as well as event-by-event data acquisition using the computer to make decisions at the molecular level, the basis of correlation mass spectrometry, a unique feature of 252Cf-PD. 

Mass Spectral Analysis of KAS Precursor. Fast atom bombardment (FAB) is the only technique that can be used for salts like the KAS precursor. FiAB requires that the sample be dispersed in a non-interactive matrix for analysis. Unfortunately, all three typical matrix materials, viz. TEA, p-nitrobenzylalcohol (NBA) and glycerol, interact/react with the sample. This problem was encountered during analysis of the spinel precursor (72). NBA was found to interact least with the spinel precursor and was used as the matrix in those studies (72). On this basis, an NBA matrix was used with the KAS precursor. EG can also be used as matrix but its high vapor pressure compared to other matrix materials, leads to much lower intensities for ion fragments. Results of FAB analyses done in both EG and NBA are shown in Table II. At the outset, nominal mass analysis by positive ion FAB were in accord with expectations. The molecular ion peak expected from the proposed precursor structure was seen, along with peaks resulting from interaction with the NBA matrix (Table II). 

By passing a continuous flow of solvent (admixed with a matrix material) from an LC column to a target area on the end of a probe tip and then bombarding the target with fast atoms or ions, secondary positive or negative ions are ejected from the surface of the liquid. These ions are then extracted into the analyzer of a mass spectrometer for measurement of a mass spectrum. As mixture components emerge from the LC column, their mass spectra are obtained. 

In conventional FAB (see Section 3.2.3), the analyte is mixed with an appropriate matrix material and applied to the end of a probe where it is bombarded with a fast-atom, or latterly, a fast-ion, beam. There are two major considerations when linking HPLC to such a system, namely (a) how is the matrix material, which is crucial for effective ionization in conventional FAB, to be incorporated into the system, and (b) how is the flowing HPLC system to be continuously presented to the ionizing beam ... 

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