Unraveling the complexity of the lipidome requires
the development of novel approaches for the structural characterization of
lipid species with isomeric resolution. Herein,
we introduce an online photochemical approach for lipid isomer identification
through selective derivatization of double bonds by reaction with singlet
oxygen. Lipid hydroperoxide products are
generated promptly after laser irradiation. Fragmentation of these species in a mass spectrometer produces diagnostic
fragments, which reveal the C=C locations in the unreacted lipids. This
approach uses an inexpensive light source and photosensitizer making it easy to
incorporate into any lipidomics workflow. We demonstrate the utility of this
approach for the shotgun profiling of C=C locations in different lipid classes present
in tissue extracts using electrospray
ionization (ESI) and for spatially-resolved analysis of lipids in tissue sections using nanospray desorption electrospray ionization (nano-DESI). These results provide a path for both
rapid profiling and ambient imaging of positional isomers in biological samples.
Rapid Profiling of Isomeric Unsaturated Lipids Through Online Photochemical Derivatization of C=C Bonds