Fast atom bombardment

File:FAB MS.jpg

ThermoQuest AvantGarde MS with quadrupole detector and FAB/EI source.

Fast atom bombardment (FAB) is an ionization technique used in mass spectrometry in which a beam of high energy atoms strikes a surface to create ions. It was developed by Michael Barber at the University of Manchester. When a beam of high energy ions is used instead of atoms, the method is known as liquid secondary ion mass spectrometry. The material to be analyzed is mixed with a non-volatile chemical protection environment called a matrix and is bombarded under vacuum with a high energy (4000 to 10,000 electron volts) beam of atoms. The atoms are typically from an inert gas such as argon or xenon. Common matrices include glycerol, thioglycerol, 3-nitrobenzyl alcohol (3-NBA), 18-crown-6 ether, 2-nitrophenyloctyl ether, sulfolane, diethanolamine, and triethanolamine. This technique is similar to secondary ion mass spectrometry and plasma desorption mass spectrometry.

How it works

FAB is a relatively low fragmentation (soft) ionization technique and produces primarily intact protonated molecules denoted as [M + H]⁺ and deprotonated molecules such as [M - H]⁻. The nature of its ionization mechanism is similar to electrospray ionization and matrix-assisted laser desorption/ionization (MALDI).

Applications

The first example of the practical application of this technique was the elucidation of the amino acid sequence of the oligopeptide efrapeptin D. This contained a variety of very unusual amino acid residues. The sequence was shown to be: N-acetyl-L-pip-AIB-L-pip-AIB-AIB-L-leu-beta-ala-gly-AIB-AIB-L-pip-AIB-gly-L-leu-L-iva-AIB-X. PIP = pipecolic acid, AIB = alpha-amino-isobutyric acid, leu = leucine, iva = isovaline, gly = glycine. This is a potent inhibitor of the mitochodrial ATPase activity.