Analyses of lipids and oxidation products by partition chromatography. Dimeric and polymeric products

A liquid-partition chromatographic method was developed to determine dimers in fats. Silicie acid treated with 20% methanol in benzene served as the immobile phase. A mixture of 2% methanol in benzene was the mobile solvent. Chromatographic separation of free fatty acids from oxidized-deodorized oils gave three well-isolated fractions composed of unoxidized acids, dimeric or polymeric fatty acids, and polar fraction (ethyl ether eluate). Recovery of acidic materials from the column was essentially quantitative (96–100%), reproducibility was good, and the standard error of regression was ±0.26. A linear relationship exists between the dimer content of deodorized soybean oil and the peroxide value of the oil before deodorization. An increase of 1% in dimer concentration corresponds to an increase in peroxide value of approximately 40. Dimer content of different vegetable oils varied from 1 to 3%. The chromatographic method can be used to estimate the degree of oxidation that an oil has received before deodorization and to follow various phases of fat oxidation, polymerization, and processing. Presented at spring meeting, American Oil Chemists' Society, Dallas, Tex., April 4–6, 1960. This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U.S. Department of Agriculture.