Utility of nicotinoyl derivatives in structural studies of mono‐ and diacylglycerols by gas chromatography/mass spectrometry. Part 1

The 1- and 2-monoacylglycerols and 1,2- and 1,3-diacylglycerols of saturated and unbranched fatty acids with 8, 10, 12, 14, 16 and 18 carbon atoms were synthesized and subsequently derivatized with nicotinic acid chloride hydrochloride. The resulting nicotinoyl derivatives were examined by mass spectrometry in the case of pure substances and as mixtures by gas chromatography/mass spectrometry (GC/MS). From the electron impact mass spectra, differentiation between mono- and diacylglycerols and between the two positional isomers of mono-acylglycerols and diacylglycerols is possible. The molecular masses of the partial acylglycerols and the identities of the bonded fatty acid were also determined. Similarly to the nicotinoyl derivatives of saturated fatty alcohols, the nicotinoyl derivatives of partial acylglycerols produce a fragmentation pattern that reflects every methylene group of the alkyl chains. These results offer rules for the structure elucidation of partially acylated acylglycerols and probably for mixed diacylglycerols by means of GC/MS, which includes the detection of double bonds and methyl branch positions at the fatty acid alkyl chains. The molecular formulae of all the important fragments in the mass spectra of the nicotinoyl derivatives were confirmed by high-resolution mass spectrometry. Their structures and fragmentation pathways are proposed.