Fast Atom Bombardment (FAB ) in mass spectrometry is a method of ionizing polar thermally unstable compounds.
The sample is added to a non-volatile matrix (e.g. glycerin , thioglycerin, nitrobenzyl alcohol ). Then in a vacuum it is exposed to a high-energy (8 - 35 keV) atomic beam (usually an inert gas such as argon or xenon is used ) or ions (Cs +). As a result, ions of the type [M + H] + and [MH] - are formed, as well as some fragments similar to those formed by ionization by electron impact with an electron energy in the range of 15–25 eV.
The matrix plays a central role (energy distribution, protonization ), but the influence of the matrix has not yet been fully studied. The disadvantage of this method is the presence of a signal from the matrix molecules, which impinges on the spectrum of the test sample.