Measurement of phospholipids by hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry: The determination of choline containing compounds in foods

A hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC LC–MS/MS) method using multiple scan modes was developed to separate and quantify 11 compounds and lipid classes including acetylcholine (AcCho), betaine (Bet), choline (Cho), glycerophosphocholine (GPC), lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphocholine (PCho) and sphingomyelin (SM). This includes all of the major choline-containing compounds found in foods. The method offers advantages over other LC methods since HILIC chromatography is readily compatible with electrospray ionization and results in higher sensitivity and improved peak shapes. The LC–MS/MS method allows quantification of all choline-containing compounds in a single run. Tests of method suitability indicated linear ranges of approximately 0.25–25 μg/ml for PI and PE, 0.5–50 μg/ml for PC, 0.05–5 μg/ml for SM and LPC, 0.5–25 μg/ml for LPE, 0.02–5 μg/ml for Cho, and 0.08–8 μg/ml for Bet, respectively. Accuracies of 83–105% with precisions of 1.6–13.2% RSD were achieved for standards over a wide range of concentrations, demonstrating that this method will be suitable for food analysis. 8 polar lipid classes were found in a lipid extract of egg yolk and different species of the same class were differentiated based on their molecular weights and fragment ion information. PC and PE were found to be the most abundant lipid classes consisting of 71% and 18% of the total phospholipids in egg yolk.