Characterization of lipid carbon-carbon double-bond isomerism via ion mobility-mass spectrometry (IMS-MS) combined with cuprous ion-induced fragmentation.

Characterization of phospholipid isomers is challenging due to their identical masses and similarities in structures. Here, we report that copper (I) ion complexed with phospholipids can be used to characterize both carbon-carbon double-bond (C=C bond) positional and geometric isomers. We investigate the distinct fragmentation patterns induced by the π-Cu interaction and developed strategies to rapidly characterize the isomerism of phospholipids. The multi-stage fragmentation of Cu-adducted lipids by collision-induced dissociation can generate diagnostic ions to locate C=C bonds in unsaturated lipids. Furthermore, the collision cross sections of Cu-adducted parent lipids and product ions can be used as molecular descriptors in distinguishing C=C bond geometric isomers. A bovine heart lipid extract containing Z-configuration lipids spiked with an E-configuration lipid was analyzed to demonstrate rapidness and effectiveness of the method in distinguishing lipid geometric isomers from a real sample.