Chromatographic studies on oxidative and thermal fatty acid dimers

A chromatographic study was carried out to investigate the nature of polymeric products in edible oils. Dimers from low‐temp oxidation of methyl linoleate were compared with thermal dimers from high‐temp polymerization of conjugated methyl linoleate. The distilled dimers were subjected to liquid‐partition chromatographic separations on silicic acid columns as methyl esters, as free acids, and as methyl esters prepared by saponification and reesterification. Chromatographically isolated dimer fractions were also rechromatographed before and after each treatment. When thermal dimer esters are saponified and reesterified, chromatographic recoveries are quantitative, and the expected changes in polarity result; whereas, with oxidative dimer esters, gross changes in polarity occur. Chromatographic separations of dimer esters or their acids fractionate into distinct areas of increasing polarity.