An improved SPE method for fractionation and identification of phospholipids

This work reports an efficient and universal SPE method developed for separation and identification of phospholipids derived from complex biological samples. For the separation step, sequential combination of silica gel-aminopropyl-silica gel SPE cartridges is applied. This setup enables separation of phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidic acid, phosphatidylinositol, phosphatidylserine, cardiolipin, and sphingomyelin into four fractions according to the polarity of their headgroups. Sample acquisition of the SPE fractions is performed by a high-resolution LC-MS system consisting of a hybrid linear IT Fourier transform ion cyclotron resonance mass spectrometer coupled to RP-HPLC. The unequivocal advantage of our SPE sample preparation setup is avoidance of analyte peak overlapping in the determination step done by RP-HPLC. Overlapping phospholipid signals would otherwise exert adverse ion suppression effects. An additional benefit of this method is the elimination of polar and nonpolar (e.g. neutral lipids) contaminants from the phospholipid fractions, which highly reduces contamination of the LC-MS system. The method was validated with fermentation samples of organic waste, where 78 distinct phospholipid and sphingomyelin species belonging to six lipid classes were successfully identified.