A Comprehensive UHPLC Ion Mobility Quadrupole Time-of-Flight Method for Profiling and Quantification of Eicosanoids, Other Oxylipins, and Fatty Acids

Analysis
of oxylipins by liquid chromatography mass spectrometry
(LC/MS) is challenging because of the small mass range occupied by
this diverse lipid class, the presence of numerous structural isomers,
and their low abundance in biological samples. Although highly sensitive
LC/MS/MS methods are commonly used, further separation is achievable
by using drift tube ion mobility coupled with high-resolution mass
spectrometry (DTIM-MS). Herein, we present a combined analytical and
computational method for the identification of oxylipins and fatty
acids. We use a reversed-phase LC/DTIM-MS workflow able to profile
and quantify (based on chromatographic peak area) the oxylipin and
fatty acid content of biological samples while simultaneously acquiring
full scan and product ion spectra. The information regarding accurate
mass, collision-cross-section values in nitrogen (DTCCSN2), and retention times of the species found are compared
to an internal library of lipid standards as well as the LIPID MAPS
Structure Database by using specifically developed processing tools.
Features detected within the DTCCSN2 and m/z ranges of the analyzed standards are
flagged as oxylipin-like species, which can be further characterized
using drift-time alignment of product and precursor ions distinctive
of DTIM-MS. This not only helps identification by reducing the number
of annotations from LIPID MAPS but also guides discovery studies of
potentially novel species. Testing the methodology on Salmonella
enterica serovar Typhimurium-infected murine bone-marrow-derived
macrophages and thrombin activated human platelets yields results
in agreement with literature. This workflow has also annotated features
as potentially novel oxylipins, confirming its ability in providing
further insights into lipid analysis of biological samples.