Confirmatory mass‐spectral data for cyclic fatty acid monomers

Abstract

AbstractCyclic fatty acid monomers (CFAM) are degradation products found in heat‐abused edible oils. This study confirms previously published data and reports the structural elucidation of hydrogenated and deuterated monocyclic and bicyclic CFAM prepared from the corresponding unsaturated species that were previously isolated from heated flaxseed (linseed) oil. CFAM structures were determined as 2‐alkyl‐4,4‐dimethyloxazoline derivatives by using gas chromatography‐electron ionization mass spectrometry. The observed retention times for the deuterated CFAM were about 0.1 min shorter than those of the corresponding hydrogenated species. For two minor six‐membered ring CFAM components, an increase in the mass of the unsaturated ring by eight mass units upon deuteration indicated the addition of four deuterium atoms to two double bonds in that ring. These data unequivocally confirmed the identity of cyclohexadienyl CFAM species in the original CFAM mixture that was isolated from heated linseed oil. The observed electron ionization mass spectrometic data for minor hydrogenated and deuterated CFAM species, which correspond 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 confirmed for all saturated CFAM mixture components. The presence of a pair of deuterium atoms on two adjacent carbon atoms further confirmed the previously determined double‐bond position along the fatty acid chain of the corresponding parent (unsaturated) compound.