Disentangling Lipid Isomers by High-Resolution Differential Ion Mobility Spectrometry/Ozone-Induced Dissociation of Metalated Species

The preponderance and functional importance of isomeric biomolecules have become topical in biochemistry. Therefore, one must distinguish and identify all such forms across compound classes, over a wide dynamic range as minor species often have critical activities. With all the power of modern mass spectrometry for compositional assignments by accurate mass, the identical precursor and often fragment ion masses render this task a steep challenge. This is recognized in proteomics and epigenetics, where proteoforms are disentangled and characterized employing novel separations and non-ergodic dissociation mechanisms. This issue is equally pertinent to lipidomics, where the lack of isomeric depth has thwarted the deciphering of functional networks. Here we introduce a new platform, where the isomeric lipids separated by high-resolution differential ion mobility spectrometry (FAIMS) are identified using ozone-induced dissociation (OzID). Cationization by metals (here K+, Ag+, and especially Cu+) broadly improves the FAIMS resolution of isomers with alternative C=C double bond (DB) positions or stereochemistry, presumably via metal attaching to the DB and reshaping the ion around it. However, the OzID yield diminishes for Ag+ and vanishes for Cu+ adducts. Argentination still strikes the best compromise between efficient separation and diagnostic fragmentation for optimal FAIMS/OzID performance.

Automated summary

The prevalence and functional importance of isomeric biomolecules in biochemistry is a hot topic, but identifying and distinguishing them can be challenging due to identical mass. Modern mass spectrometry offers compositional assignments, but proteomics and lipidomics are still facing difficulties in deciphering functional networks due to lack of isomeric depth. The introduction of a new platform utilizing high-resolution differential ion mobility spectrometry (FAIMS) and ozone-induced dissociation (OzID) provides a solution for identifying isomeric lipids. Metal cationization improves FAIMS resolution, but the yield diminishes for certain metals like Cu+. Argentination strikes a balance between separation efficiency and diagnostic fragmentation for optimal FAIMS/OzID performance.