Structural Analysis of Phospholipid Using Hydrogen Abstraction Dissociation and Oxygen Attachment Dissociation in Tandem Mass Spectrometry.

Gas-phase hydrogen radicals were introduced into a quadrupole ion trap containing singly charged phospholipids to obtain structural fragmentation patterns in tandem mass spectrometry (MS/MS). Saturated and unsaturated phosphatidylcholines were used as a model phospholipid, whose chain-length ranges between 16 and 24. The MS/MS spectrum yielded a continuous series of fragment ions with a mass difference of 14 Da, representing the saturated fatty acyl chains. The fragment ions corresponding to the double-bond position within a single fatty acyl chain showed a characteristic mass difference of 12 Da. The detection of these diagnostic product ions enabled the structural analysis of double-bond isomers of phospholipids. To further investigate the potential of radical-induced dissociation for the isomeric analysis of phospholipids, gas-phase hydroxyl radicals, and triplet oxygen atoms were employed in tandem mass spectrometry. The methylene bridges adjacent to the double-bond positions were selectively dissociated, accompanied by oxidation of the double bonds. Tandem mass spectrometry incorporating multiple radical species facilitates the structural analysis of isomeric phospholipids.