Analysis of the oxidation products of cis- and trans-octadecenoate methyl esters by capillary gas chromatography-ion-trap mass spectrometry. I. Epoxide and dimeric compounds.

The oxidative behavior of methyl oleate (MeOl) and methyl elaidate (MeEl) was compared by hyphenated chromatographic techniques. MeOl and MeEl were separately oxidized (200 degrees C/30 min) and subjected to solid-phase extraction, in order to isolate the low polarity compounds. The two isomeric 9,10-epoxystearic methyl esters formed in both MeOl and MeEl at different threolerythro ratios (2.3 and 6.2%, respectively). The dimeric products produced in the thermoxidized MeOl and MeEl (1.4 and 1.6%, respectively), showed similar gas chromatographic characteristics and mass spectra, suggesting similar molecular structures and formation mechanisms. A positional and probably configurational mixture of symmetric and asymmetric dehydrodimers was detected, whereas the occurrence of MeEl or MeOl dimeric ethers is to be confirmed.