Human milk triacylglycerols (TAG) were analyzed by ammonia negative ion chemical ionization tandem mass spectrometry. The deprotonated molecular ions of triacylglycerols were fractionated at the first mass spectrometry (MS) stage. Twenty-nine of the deprotonated TAG ions were further analyzed based on their collisionally activated (CA) spectra. The tandem MS analysis covered eleven major acyl carbon number fractions, two of which contained odd carbon number fatty acids. Fatty acids of 28 different molecular weights were recorded from the daughter spectra. Hexadecanoic acid was present in all CA spectra, octadecenoic acid in the CA spectra of all mono- and higher unsaturated TAG, and octadecadienoic acid in the CA spectra of all di- and higher unsaturated TAG. The major fatty acid combinations in triacylglycerols were: with 0 double bonds (DB), 12.0/12:0/16:0, with 1 DB, 12.0/16:0/18:1; with 2 DB, 16:0/18:1/18:1; with 3 DB, 16:0/18:2/18:1; with 4 DB, 18:2/18:1/18:1; and with 5 DB, 18:2/18:2/18:1; hexadecanoic acid typically occupied the sn-2 position. The most abundant TAG was shown to be sn-18:1-16:0-18:1, comprising about 10% of all triacylglycerols.
