FAST ATOM BOMBARDMENT COMBINED WITH TANDEM MASS SPECTROMETRY FOR THE STUDY OF COLLISIONALLY INDUCED REMOTE CHARGE SITE DECOMPOSITIONS.

Several classes of FAB desorbed, closed-shell ions have been found to decompose upon collisional activation in an unprecedented manner. The fragmentation occurs for ions with long alkyl chains and involves parallel losses of the elements of C//nH//2//n// plus //2 initiated from the alkyl terminus. The mechanism appears to be a 1,4-elimination of H//2 to give a neutral alkene (C//nH//2//n) and an unsaturated charged fragment. The reactions do not rely on charge initiation and, as a result, they are termed 'remote charge site fragmentations. ' Considerable structural information may be obtained by interpreting the spectra of daughter ions. The information includes location of double bonds in fatty acids, indentification of components in complex lipids, determination of compositions of anionic and cationic surfactants, and identification of long-chained alkyl substituents on phosphonium and ammonium ions.