Electrospray ionization for analysis of platelet‐activating factor

Platelet‐activating factor (PAF) was analyzed by electrospray‐ionization spectrometry (ESI‐MS) using a single quadrupole mass spectrometer. The positive‐ion spectrum was dominated by an ion corresponding to a sodiated molecule when a low potential difference between the capillary exit (nozzle) and the skimmer was employed, but when the capillary exit voltage was increased, fragmentation of PAF was observed. Initial fragmentation involved the loss of the elements of trimethylamine from the sodiated molecule to yield [M+Na−59]⁺. An intense ion at m/z 147, generated by the loss of trimethylamine from the sodiated phosphocholine portion of the molecule was also detected, along with a lower intensity ion at m/z 184 which is representative of a protonated phosphocholine moiety. With negative‐ion detection the major molecular species was [M + Cl]⁻. Interpretation of the mass spectral fragments was verified by ESI tandem mass spectrometry on a triple‐quadrupole tandem mass spectrometer.