Identification of milk fat triacylglycerols by capillary supercritical fluid chromatography-atmospheric pressure chemical ionization mass spectrometry.

Identification of milk fat triacylglycerols was accomplished by capillary supercritical fluid chromatography (SFC) combined with atmospheric pressure chemical ionization mass spectrometry [(APCI)MS]. Supercritical carbon dioxide was the carrier fluid in SFC. Ionization was achieved by introducing vapor of ammonia in methanol into the ionization chamber which resulted in the formation of abundant [M + 18]+ and [M - RCCO]+ ions of triaclyglycerols. These ions defined both the molecular weight and the fatty acid constituents of a triacylglycerol, respectively. SFC on a nonpolar stationary phase provided an efficient separation of triacylglycerols according to the combined number of carbon atoms in the acyl chains a molecule. In addition to the identification of the major chromatographic peaks representing molecules with 26-54 acyl carbons, minor peaks representing triacylglycerols with an odd number of acyl carbons were separated and identified. Furthermore, compositional information on partially separated isobaric triacylglycerols, which differed substantially in the chain length of the fatty acyl residues, was achieved within some of the peaks. A new finding of the present study was the formation of abundant [M + 18]+ ions of saturated triacylglycerols in addition to diagnostic fragment ions,being of primary importance in structure elucidation. This extends the applicability of capillary SFC-(APCI)MS in the analysis of both saturated and unsaturated triacylglycerols.