Characterization of the neutral products formed upon the charge-remote fragmentation of fatty acid ions.

Collisionally activated dissociation (CAD) of the carboxylate anions, [M-H]-, or dilithiated cations, [M-H+2Li]+, from fatty acids results in charge-remote fragmentations at the alkyl chain C-C bonds leading to structure-indicative fragment ions. The neutral molecules eliminated during these reactions are characterized in this study using neutralization-reionization mass spectrometry (NRMS). The major neutral losses detected are alkenes (or dienes, in the case of monounsaturated fatty acids), not alkanes or alkyl radicals. This is consistent with the initially proposed mechanism proceeding by a pericyclic 1,4-elimination of H2.