Analysis of Hydroxyl, Unsaturated, and Cyclopropane Fatty Acids by High Pressure Liquid Chromatography

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Abstract
The investigation describes the HPLC separation of hydroxyl fatty acids as their methoxyphenacyl esters. All separations were performed using two types of reverse phase columns, μ-Bondapak C 18 and Fatty Acid Analysis columns. The solvent system consisted of acetonitrile: water gradient. A simple method for the trifluoroacetylation of the hydroxyl group is described which permits the identification of these specific fatty acids and decreases the lower limit in chain length determination for these fatty acids. A method for the hydrogenation of unsaturated fatty acid mixtures is described, and the effects of variations in time, temperature, pressure, and the amount of catalyst are examined on the percent hydrogenation of unsaturated to the saturated forms of the fatty acids. Further, the effects of the different variables are related to the percent of hydrogenation of the cyclopropane fatty acids. Evidence is provided on the hydrogenation of the cyclopropane which does not agree with previously described ring opening mechanisms which have been proposed from GLC data which may be due to the difference in temperatures under which the chromatographic processes are carried out. These findings indicated the possibility of isolating an intermediate in the process by HPLC.