Characterization of alkylacyl, alk-1-enylacyl and lyso subclasses of glycerophosphocholine by tandem quadrupole mass spectrometry with electrospray ionization

Positive ion tandem quadrupole mass spectrometric methods for structural characterization of the subclasses of sn-glycero-3-phosphocholine (PC), including alkylacyl- and alk-1-enylacylphosphocholine and lysophosphatidylcholine (LPC), are described. Following collisionally activated dissociation, the [M + Li]⁺ ions generated by electrospray ionization yield abundant informative fragment ions that permit structural determination, and distinction of regioisomers among lysophosphatidylcholine can be easily achieved. In contrast, structurally informative ions arising from [M + H]⁺ or [M + Na]+ ions are less prominent. The most abundant ion observed in the product-ion spectra of the [M + Li]⁺ ions of plasmenyl- and plasmanyl-PC and of LPC arises from loss of N(CH₃)₃ ([M + Li - 59]⁺). This feature permits their distinction from a product-ion spectrum arising from a diacylphosphatidylcholine, in which the [M + Li - 183]⁺ ion reflecting loss of phosphocholine is the most prominent. Examples for identification of various subclasses of PC in biological extracts by tandem mass spectrometry applying various constant neutral loss scannings are also shown.