Fast atom bombardment and tandem mass spectrometry for determing iso- and anteiso-fatty acids

Branched fatty acids can be distinguished from isomeric straight chain fatty acids by collisionally activating the (M-H)⁻ ions desorbed by using fast atom bombardment (FAB) mass spectrometry (MS). In particular, an acid with iso- fatty branching can be readily distinguished from one containing anteiso- branching; the latter undergoes loss of the elements of CH₄ and C₂H₆ but not C₃H₈. These decompositions are another example of remote charge site fragmentation. Mixtures of homologs and isomers can be investigated by using the combination of FAB and tandem mass spectrometry (MS-MS).