Rapid identification of fatty acids and (O-acyl)-ω-hydroxy fatty acids in human meibum by liquid chromatography/high-resolution mass spectrometry.

We report a rapid liquid chromatography/quadrupole Orbitrap Fourier transform mass spectrometry (LC-FTMS) method for identifying free fatty acids (FAs) and (O-acyl)-ω-hydroxyFAs (OAHFAs) in human meibum without derivatization. Meibum is a lipid-rich secretion and an important component of the tear film lipid layer. FAs are commonly detected by gas chromatography (GC) or GC/MS after methyl ester derivatization. We developed high-throughput lipid profiling using LC-FTMS and lipid identification software, Lipid Search, without derivatization and applied the method to human meibum. Chromatographic separation was performed on a C18 column. We selected negative electrospray ionization [M-H](-), and applied high-resolution full scan mode to FA analysis and data-dependent MS(2) mode to OAHFA analysis. High-resolution Orbitrap MS proved to be an excellent tool for the rapid analysis of lipids from meibum, and 100 FA and 61 OAHFA molecular species were detected. The analysis times were 12 and 16.5min, respectively. Very long chain FAs (up to C37) and OAHFAs (up to C56) were also detected. The results clearly showed that retention time correlates with the number of double bonds and carbon chains. This LC/MS method can be applied to the identification of FAs and OAHFAs in human meibum.