Analyses of Vegetable Oil Triacylglycerols by Silver Ion High Performance Liquid Chromatography with Flame Ionization Detection

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Abstract
Silver ion high performance liquid chromatography with a commercially available column with a simple isocratic mobile phase of acetonitrile in hexane and flame ionization detection was employed to separate and quantitate triacylglycerol species of vegetable oils. Coconut, palm, cottonseed, olive, safflower, sunflower, corn, pumpkinseed, linseed, soybean, and canola oils were analyzed, as well as randomized corn and soybean oils, and the blends and interesterified products of corn and soybean oil with cottonseed oil stearine. Fractionated triacylglycerol species were identified by gas chromatography of their methyl esters. Triacylglycerol composition was obtained by reversed phase and silver ion high performance liquid chromatography of the same oil. Oil fatty acid composition was determined by gas chromatography of the transmethylated oil and correlated with that calculated from the triacylglycerol composition by silver ion chromatography of the same oil. The triacylglycerol separation was mostly based on the total unsaturation of the fatty acids attached to the glycerol moiety. However, partial separation of triacylglycerols with the same unsaturation content but different fatty acids indicates that other separation mechanisms, in addition to fatty acid complexation with silver ions, such as adsorption and partition, are involved. The flame ionization response (area percent) was determined to be proportional to weight percent for oil triacylglycerol composition. In addition to analyses of vegetable oils, the efficacy of the silver ion high performance liquid chromatography method with flame ionization detection for analyses of margarine base stocks produced from corn and soybean oils was demonstrated.