The Fast-Atom Bombardment Method

The basic method involves the addition of a source of fast atoms to a conventional mass spectrometer. This neutral atom beam is directed 

The factor that makes FAB-MS so different from EI-MS is that, in its usual form, the sample coating the probe tip consists of a solution or suspension in a relatively nonvolatile matrix liquid such as glycerol. This provides for a continually renewed surface exposed to the atom beam and thus spectra that are stable over a period of many minutes. No heating of the sample is required other than the localized energy implanted in the sample by the atom beam. Although complications may result from interactions with the matrix liquid, they are often less than, or certainly no worse than, such complications as thermal decomposition or ion molecule reactions, involved in other techniques for sample volatilization. In addition, FAB-MS is looking at condensed-phase systems similar to those investigated by NMR or IR. Thus perhaps the data are easier to correlate. Several reviews or introductions to the method have appeared (4, 7-9,13, 15-22). 

The study of various doping materials in a FAB matrix can, in fact, lead to the determination of chemical equilibrium constants as demonstrated by Caprioli (31) who was able to measure the pKa values of a series of acids. 

It is also possible to do the FAB experiment on solid materials without the presence of a matrix liquid. In such cases, the lifetime of the observed spectra is very much shorter but often adequate to characterize the material of interest. We have had considerable success with 

A new and promising matrix for less polar organometallics and coordination compounds is p-nitrophenyl octyl ether. 

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