Development of a lipid profiling system using reverse-phase liquid chromatography coupled to high-resolution mass spectrometry with rapid polarity switching and an automated lipid identification software.

Lipidomics requires accurate lipid profiling, which until recently has been challenging at best. In the present study, we developed a practical workflow for high-throughput and exhaustive lipid profiling by combining reverse-phase liquid chromatography coupled to quadrupole orbitrap Fourier transform mass spectrometry, with an automated lipid identification software. This validated method enables highly sensitive and simultaneous analysis of lipids with varying polarities such as glycerophospholipids and sphingophospholipids, by switching the acquisition polarities in mass spectrometry. In addition, it facilitates data-dependent MS(2) analysis targeting the lipid molecular species without any influence from other ions by setting the inclusion list, the target m/z list for the product ion scanning. The m/z values of the target lipid molecular species, stored in the database of Lipid Search software, are added to the inclusion list. Moreover, optimizing the identification conditions of the software for the LC/MS system enables high-throughput and accurate identification of lipid molecular species existing in biological samples. Specifically, LC separation is essential for accurate identification of lipid molecular species that possess some fatty acid chains, because it can be difficult to determine fatty acid chain composition of detected molecular species especially in triacylglycerol compounds in direct infusion mass spectrometry. This method has high reproducibility and can be used for structural analysis even for low-abundance compounds. Using this method, over 400 lipid compounds targeted in this research were detected and identified from a sample of mouse plasma. This result indicates that the LC/MS method in the present study enables efficient lipid profiling.