Piperidine ester derivatives in mass spectrometric analysis of fatty acids from human serum phospholipids and cholesteryl esters.

When fatty acids with unknown structural features are confronted in mass spectral analyses of complex mixtures the cleavage pattern from the widely used methyl ester derivatives is not always sufficiently informative. Their mass spectra often contain only weak signals for the parent or any other characteristic ions. Hence the advantages of piperidides were explored and compared with methyl esters in the structure elucidation of fatty acids from human serum phospholipids and cholesteryl esters. After separation with thin-layer chromatography the fractions were extracted and subjected to alkaline hydrolysis. Methyl esters were prepared using HCl-methanol. Piperidides were obtained by converting the fatty acids first to acyl chlorides via interaction with thionyl chloride and then to piperidyl carboxylates by action with 3-(hydroxymethyl)-N-methylpiperidine. The piperidide derivatives were found more suitable than the methyl esters for the structural analysis of fatty acids because the chain structure can be diagnostically examined according to the specific fragmentation induced by the radical cleavage.