Fast Atom Bombardment (FAB) or Liquid Secondary Ionization (LSI)
In this technique, the sample is first dissolved in a low-pressure liquid, like glycerol or 3-nitrobenzyl alcohol. The mixture is not crystallized as done in MALDI, but instead a few microlitres of this liquid are placed on a small metal target at the end of a probe, which is inserted into MS.

The liquid surface is then bombarded with a beam of high kinetic energy atoms (xenon or argon) or ions (caesium) rather than laser used in MALDI. Molecules are sputtered from the surface is then bombarded with a beam of high kinetic energy atoms (xenon or argon) or ions (caesium) rather than laser used in MALDI. Molecules are sputtered from the surface, enter the gas phase and ionize.