Revolutions in Lipid Isomer Resolution: Application of Ultrahigh-Resolution Ion Mobility to Reveal Lipid Diversity
Berwyck L. J. Poad, Lachlan J. Jekimovs, Reuben S. E. Young, Puttandon Wongsomboon, David L. Marshall, Felicia Hansen, Therese M. Fulloon, Michael C. Pfrunder, Tyren M. Dodgen, Mark Ritchie, Stephen C. C. Wong, Stephen J. Blanksby
Abstract
Many families of lipid isomers remain unresolved by contemporary liquid chromatography–mass spectrometry approaches, leading to a significant underestimation of the structural diversity within the lipidome. While ion mobility coupled to mass spectrometry has provided an additional dimension of lipid isomer resolution, some isomers require a resolving power beyond the capabilities of conventional platforms. Here, we present the application of high-resolution traveling-wave ion mobility for the separation of lipid isomers that differ in (i) the location of a single carbon–carbon double bond, (ii) the stereochemistry of the double bond ( cis or trans ), or, for glycerolipids, (iii) the relative substitution of acyl chains on the glycerol backbone ( sn -position). Collisional activation following mobility separation allowed identification of the carbon–carbon double-bond position and sn -position, enabling confident interpretation of variations in mobility peak abundance. To demonstrate the applicability of this method, double-bond and sn -position isomers of an abundant phosphatidylcholine composition were resolved in extracts from a prostate cancer cell line and identified by comparison to pure isomer reference standards, revealing the presence of up to six isomers. These findings suggest that ultrahigh-resolution ion mobility has broad potential for isomer-resolved lipidomics and is attractive to consider for future integration with other modes of ion activation, thereby bringing together advanced orthogonal separations and structure elucidation to provide a more complete picture of the lipidome.