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 °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 threo/erythro 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.