Selective enrichment of phosphatidylcholines from food and biological matrices using metal oxides as solid-phase extraction materials prior to analysis by HPLC-ESI-MS/MS

A zirconia (ZrO(2))-modified solid-phase extraction sorbent has been evaluated for selective extraction of phosphatidylcholines from biological samples, followed by analysis of the isolated solutes by reversed-phase liquid chromatography-electrospray ionization-tandem mass spectrometry. The clean-up process was optimized using seven standard phosphatidylcholines including two lyso derivatives. Different acidic conditions were tested for the bonding and washing steps; for elution, various aqueous or methanolic bases were studied. Experiments were conducted hydrodynamically using extraction cartridges, and statically in batch mode; the performance of the sorbent was significantly better when used in the flow-through mode. The developed clean-up procedure was used to selectively enrich phosphatidylcholines from whole milk, human plasma, and mouse plasma, to show the wide applicability of the method. For the preceding extraction of total lipids from the matrix, different solvent mixtures (methanol-chloroform, methanol-methyl tert-butyl ether, and ethanol-ethyl acetate) were compared. Accuracy and reproducibility of the proposed sample-preparation procedure were evaluated. Matrix effects possibly affecting mass spectrometric analysis were studied before and after the solid-phase extraction. They were found to be significant for several analytes, stressing the importance of a sample clean-up procedure. Under identical experimental conditions, recovery of bound phosphatidylcholines by zirconia was superior to that by other metal oxides, for example titania (TiO(2)) and stannia (SnO(2)).