Electron-induced dissociation (EID) for structure characterization of glycerophosphatidylcholine: determination of double-bond positions and localization of acyl chains.

Glycerophospholipids are a highly abundant and diverse collection of biologically relevant lipids, and distinction between isomeric and isobaric species is a fundamental aspect for confident identification. The ability to confidently assign a unique structure to a glycerophospholipid of interest is dependent on determining the number and location of the points of unsaturation and assignment of acyl chain position. The use of high-energy electrons (>20 eV) to induce gas-phase dissociation of intact precursor ions results in diagnostic product ions for localizing double-bond positions and determining acyl chain assignment. We describe a high-resolution, tandem mass spectrometry method for structure characterization of glycerophospholipids using electron-induced dissociation (EID). Furthermore, the inclusion of nomenclature to systematically assign bond cleavage sites with acyl chain position and double-bond location enables a uniform platform for lipid identification. The EID methodology detailed here combines novel application of an electron-based dissociation technique with high-resolution mass spectrometry that facilitates a new experimental approach for lipid biomarker discovery and validation.