CONFIRMATORY MASS-SPECTRAL DATA FOR CYCLIC FATTY-ACID MONOMERS

Cyclic fatty acid monomers (CFAM) are degradation products found in he at-abused edible oils. This study confirms previously published data a nd reports the structural elucidation of hydrogenated and deuterated m onocyclic and bicyclic CFAM prepared from the corresponding unsaturate d species that were previously isolated from healed flaxseed (linseed) oil. CFAM structures were determined as 2-alkyl-4,4-dimethyloxazoline derivatives by using gas chromatography-electron ionization mass spec trometry. The observed retention times for the deuterated CFAM were ab out 0.1 min shorter than those of the corresponding hydrogenated speci es. For two minor six-membered ring CFAM components, an increase in th e mass of the unsaturated ring by eight mass units upon deuteration in dicated the addition of four deuterium atoms to two double bonds in th at ring. These data unequivocally confirmed the identity of cyclohexad ienyl CFAM species in the original CFAM mixture that was isolated from heated linseed oil. The observed electron ionization mass spectrometi c data for minor hydrogenated and deuterated CFAM species, which corre spond to the last two eluting monounsaturated species, were consistent with CFAM having bicyclic (fused 5- and 6-membered rings) structures. The location of the ring along the fatty acid chain was also confirme d for all saturated CFAM mixture components. The presence of a pair of deuterium atoms on two adjacent carbon atoms further confirmed the pr eviously determined double-bond position along the fatty acid chain of the corresponding parent (unsaturated) compound.