Hydrophilic interaction liquid chromatography – electrospray ionization - tandem mass spectrometry of a complex mixture of native and oxidized phospholipids.

A mixture of native and oxidized phospholipids (PLs), generated by the soybean lipoxygenase type V-catalyzed partial oxidation of a lipid extract obtained from human platelets, was analyzed by HydrophilicInteraction Liquid Chromatography-ElectroSpray Ionization-Tandem Mass Spectrometry (HILIC–ESI-MS/MS). The complexity of the resulting mixture was remarkable, considering that the starting lipid extract, containing (as demonstrated in a previous study) about 130 native PLs, was enriched with enzy-matically generated hydroperoxylated derivatives and chemically generated hydroxylated forms of PLsbearing polyunsaturated side chains. Nonetheless, the described analytical approach proved to be verypowerful; indeed, focusing on phosphatidylcolines (PCs), the most abundant PL class in human platelets,about fifty different native/oxidized species could be identified in a single HILIC–ESI-MS/MS run. Low-energy collision induced dissociation tandem MS (CID-MS/MS) experiments on chromatographicallyseparated species showed single neutral losses of H2O2 and H2O to be typical fragmentation pathways of hydroperoxylated PCs, whereas a single H2O loss was observed for hydroxylated ones. Moreover, diag-nostic losses of n-hexanal or n-pentanol were exploited to recognize PCs hydroperoxylated on the last butfive carbon atom of a -6 polyunsaturated side chain. Despite the low resolution of the 3D ion trap mass analyzer used, the described HILIC–ESI-MS/MS approach appears very promising for the identification ofoxidized lipids in oxidatively stressed complex biological systems.