Liquid Chromatography-Mass Spectrometry of Phospholipids in Soybean Products Using Particle Beam and Ionspray Interfaces

Particle beam (PB) high-performance liquid chromatography (HPLC)/MS and ionspray (ISP) HPLC/MS were investigated for the separation and mass spectral characterization of the phospholipids phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol. Fragmentation patterns obtained in both positive-ion and negative-ion chemical ionization modes using the PB/MS technique were not useful in differentiating phospholipid classes. The HPLC/ISP-MS technique was able to provide direct information about the molecular weights of the individual homologues; more complete characterization of the fatty acid chains and of the polar head group was obtained by using ionspray with tandem mass spectrometry (MS/MS). The HPLC/ISP-MS system was used to characterize the lipid fraction of different soybean products; phosphatidylserine and less polar lipids such as triglycerides were also identified from the on-line mass spectra of eluates. Finally, the potential of the MS/MS selected-reaction monitoring (SRM) technique for the analysis of phospholipids at the nanogram level was explored. The higher selectivity observed with SRM compared with that obtained by using selected-ion-monitoring suggests the potential of the former method for the analysis of these substances in samples with a low content, such as biological and clinical ones.