Abstract
The goal of untargeted lipidomics is to have high throughput, yet comprehensive and unambiguous identification and quantification of lipids. Novel stationary phases in LC separation and new mass spectrometric instruments capable of high mass resolving power and faster scanning rate are essential to achieving this goal. In this work, 4 reversed phase LC columns coupled with a high field quadrupole orbitrap mass spectrometer (Q Exactive HF) were thoroughly compared using complex lipid standard mixture and rat plasma and liver samples. A good separation of all lipids was achieved in 24min of gradient. The columns compared include C30 and C18 functionalization on either core-shell or totally porous silica particles, with size ranging from 1.7 to 2.6μm. Accucore C30 column showed the narrowest peaks and highest theoretical plate number, and excellent peak capacity and retention time reproducibility (<1% standard deviation). As a result, it resulted in 430 lipid species identified from rat plasma and rat liver samples with highest confidence. The high resolution offered by the up-front RPLC allowed discrimination of cis/trans isomeric lipid species, and the high field orbitrap mass spectrometer afforded the clear distinction of isobaric lipid species in full scan MS and the unambiguous assignment of sn-positional isomers for lysophospholipids in MS/MS. Taken together, the high efficiency LC separation and high mass resolving MS analysis are very promising tools for untargeted lipidomics analysis.