Mass spectrometry of the phosphatidylcholines: dipalmitoyl, dioleoyl, and stearoyl-oleoyl glycerylphosphorylcholines

Abstract

Mass spectra of the diacyl glycerylphosphorylcholines have been obtained using a direct insertion probe, with a source temperature of 250°C at an ionizing potential of 70 ev. Fragmentation patterns are described for dipalmitoyl, dioleoyl, and 1-stearoyl-2-oleoyl glycerylphosphorylcholines. Significant differences are observed in the fragmentation patterns, and the fragment ions have been identified by high resolution mass measurements. Ions associated with the hydrocarbon chains, glycerol esters, and phosphorylcholine have been identified, and the presence of metastable transitions have been used as confirmatory evidence for some of the steps involved in the fragmentation sequence. A molecular ion was tentatively identified in the case of dioleoyl glycerylphosphorylcholine. The mass spectrum of 1-stearoyl-2-oleoyl glycerylphosphorylcholine shows an important rearrangement ion at m/e 604 and some evidence for the differential cleavage, or stability, of the stearoyl- and oleoyl-containing fragments.Strong similarities exist between the observed spectra for the diacyl glycerylphosphorylcholines and those for the corresponding glycerides.

Keywords

• fragmentation
• pyrolysis
• electron impact
• molecular species