Characterization of sodiated glycerol phosphatidylcholine phospholipids by mass spectrometry.

Fast atom bombardment mass spectrometry in the positive mode was used for the characterization of sodiated glycerol phosphatidylcholines. The relative abundance (RA) of the protonated species is similar to the RA of the sodiated molecular species. The sodiated fragment ion, M + Na - 59, corresponding to the loss of trimethylamine, and other sodiated fragment ions, were also observed. The decomposition of the sodiated molecule is very similar for all the studied glycerol phosphatidylcholines, in which the most abundant ion corresponds to a neutral loss of 59 Da. Upon collision-induced dissociation (CID) of the M + Na ion informative ions are formed by the losses of the fatty acids in the sn-1 and sn-2 positions. Other major fragment ions of the sodiated molecule result from loss of non-sodiated and sodiated choline phosphate, M + Na - 183, M + Na - 184 and M + Na - 205, respectively. The main CID fragmentation pathway of the M + Na - 59 ion yields the M + Na - 183 ion, also observed in the CID spectra of the M + Na molecular ion. Other major fragment ions are M + Na - 205 and the fragment ion at m/z 147. Collisional activation of M + Na - 205 results in charge site remote fragmentation of both fatty acid alkyl chains. The terminal ions of these series of charge remote fragmentations result from loss of part of the R(1) or R(2) alkyl chain. Other major informative ions correspond to acylium ions.