A universal product ion nomenclature for [M−H]−, [M+H]+ and [M+nNa−(n − 1)H]+ (n = 1-3) glycerophospholipid precursor ions based on high-energy CID by MALDI-TOF/RTOF mass spectrometry

The fragmentation behavior of various types of precursor ions ([M−H]−, [M+H]+, [M+Na]+, [M+2Na−H]+ and [M+3Na−2H]+) of the six major classes of glycerophospholipids (glycerophosphatidic acid, glycerophosphatidylglycerol, glycerophosphatidylinositol, glycerophosphatidylserine, glycerophosphatidylethanolamine and glycerophosphatidylcholine) was studied in detail by high-energy collision-induced dissociation (CID)-TOF/RTOF mass spectrometry. Whereas negative-ion CID-spectra of the [M−H]− ion of these lipids primarily exhibited the molecular mass of the fatty acid substituents, protonated and monosodiated precursor ions showed abundant loss of the polar head group identifying the class of glycerophospholipid. In contrast, doubly and triply sodiated singly charged glycerophospholipid precursor ions not only yielded charge-remote fragmentation of the fatty acid substituents, but also several abundant low-mass product ions of diagnostic value for the identification of the phospholipid class as well as specific phosphate-related sodium adduct ions for determining the number of sodium cations attached to the precursor ion. These findings finally lead to the establishment of common fragmentation rules as well as a universal product ion nomenclature for all types of glycerophospholipid precursor ions investigated (applicable for low- and high-energy CID). This nomenclature is based on the A-, B-, C-, D-, E-, F-. and G-product ion nomenclature previously published for sodiated triacylglycerol precursor ions [C. Cheng, M.L. Gross, E. Pittenauer, Anal. Chem. 70 (1998) 4417-4426] with adaptations for the type of precursor ion and class of glycerophospholipid investigated.