Investigating the Potential of Drift Tube Ion Mobility for the Analysis of Oxidized Lipids

Epilipids,
a subset of the lipidome that comprises oxidized,
nitrated,
and halogenated lipid species, show important biochemical activity
in the regulation of redox lipid metabolism by influencing cell fate
decisions, including death, health, and aging. Due to the large chemical
diversity, reversed-phase liquid chromatography–high-resolution
mass spectrometry (RPLC-HRMS) methods have only a limited ability
to separate numerous isobaric and isomeric epilipids. Ion mobility
spectrometry (IMS) is a gas-phase separation technique that can be
combined with LC-HRMS to improve the overall peak capacity of the
analytical platform. Here, we illustrate the advantages and discuss
the current limitations of implementing IMS in LC-HRMS workflows for
the analysis of oxylipins and oxidized complex lipids. Using isomeric
mixtures of oxylipins, we demonstrated that while deprotonated ions
of eicosanoids were poorly resolved by IMS, sodium acetate and metal
adducts (e.g., Li, Na, Ag, Ba, K) of structural isomers often showed
ΔCCS% above 1.4% and base peak separation with high-resolution
demultiplexing (HRDm). The knowledge of the IM migration order was
also used as a proof of concept to help in the annotation of oxidized
complex lipids using HRDm and all-ion fragmentation spectra. Additionally,
we used a mixture of deuterium-labeled lipids for a routine system
suitability test with the purpose of improving harmonization and interoperability
of IMS data sets in (epi)lipidomics.