Identification of diacylglycerols and triacylglycerols in a structured lipid sample by atmospheric pressure chemical ionization liquid chromatography/mass spectrometry

Atmospheric pressure chemical ionization liquid chromatography/mass spectrometry was used in the identification of diacylglycerol and triarylglycerol (TAG) molecular species in a sample of a structured lipid. In the study of acyl glycerol standards, the most distinctive differences between the diacylglycerol and TAG molecules were found to be the molecular ion and the relative intensity of monoacylglycerol fragment ions. All saturated TAG ranging from tricaproin to tristearin, and unsaturated TAG including triolein, trilinolein, and trilinolenin, had ammonium adduct molecular ions [M + NH4](+). Protonated molecular ions were also produced for TAG containing unsaturated fatty acids and the intensity increased with increasing unsaturation. Diacylglycerol fragment ions were also formed for TAG. The ammonium adduct molecular ion was the base peak for TAG containing polyunsaturated fatty acids, whereas the diacylglycerol fragment ion was the base peak for TAG containing saturated and monounsaturated medium- and long-chain fatty acids; the relative intensities of the ammonium adduct molecular ions were between 14 and 58%. The most abundant ion for diacylglycerols, however, was the molecular ion [M - 17](+), and the relative intensity of the monoacylglycerol fragment ion was also higher than that for TAG. These distinctive differences between the diacylglycerol and TAG spectra were utilized for rapid identification of the acylglycerols in the sample of a structured lipid.