Determination and quantification of fatty acid C=C isomers by epoxidation reaction and liquid chromatography-mass...

The location of double bond in unsaturated fatty acids (FAs) plays a critical role in their physiological properties. However, structural identification and quantification of unsaturated FAs by mass spectrometry are still challenging. In this work, we reported the coupling of epoxidation reaction of the C=C in unsaturated FAs and liquid chromatography-mass spectrometry (LC-MS) with multiple reaction monitoring (MRM) mode for accurate identification and quantification of C=C isomers of FAs. Epoxidation of the C=C in unsaturated FAs was induced by a dioxide of ketone, tetrahydrothiopyran-4-one 1,1-dioxide, as a catalyst and Oxone as an oxidant in less than 5 min with nearly 100% yield. All the C=C bonds were epoxidized to obtain a single product, simplifying the chromatographic separation of epoxidation products to enable more accurate quantification analysis. The epoxidation products were stable at room temperature and can produce highly abundant diagnostic ions indicative of C=C locations by tandem mass spectrometry using collision-induced association (CID). The application of this approach for the analysis of FAs isomers in human plasma demonstrated the potential of our method for the qualitative and quantitative analysis of unsaturated FAs in complex biological samples, which is valuable in biological and medical analysis.