SILVER ION CHROMATOGRAPHY AND GAS-CHROMATOGRAPHY MASS-SPECTROMETRY IN THE STRUCTURAL-ANALYSIS OF CYCLIC MONOENOIC ACIDS FORMED IN FRYING OILS

The nature of the cyclic monoenoic fatty acids formed from linoleic acid in sunflower oil heated to 275-degrees-C has been determined by gas chromatography-mass spectrometry of the picolinyl ester derivatives, before and after hydrogenation and deuteration, and following simplification by silver ion high-performance liquid chromatography. In addition, they were examined by gas chromatography-Fourier transform infrared spectroscopy. Cyclopentene fatty acids (50% of the total monoenes) were formed from C-8 to C-12 and C-10 to C-14 of the original chain in equal amounts with unique stereochemistry. In some isomers the double bond appeared to remain in its original position, and in others it migrated to a substituted ring carbon. Isomers (25% of the total monoenes) were formed with a cis double bond in position 9 or 12 in equal amounts, and either a cyclopentane ring involving C-5 to C-9 or C-13 to C-17 or a cyclohexane ring involving C-5 to C-10 or C-12 to C-17 of the original fatty acid chain. With these compounds, most if not all of the possible configurational isomers were produced. Related compounds (25% of the total monoenes) with a trans double bond in position 9 or 12 were found with only six-membered rings with a restricted stereochemistry. Some bicyclic fatty acids were also present in the mixture.