Abstract
A combined capillary gas liquid chromatography (GLC) and infrared spectrophotometry (IR) method is described for the determination ofcis andtrans‐octadecenoic acids in margarines made from partially hydrogenated vegetable oils. The totaltrans‐unsaturation of margarine fatty acid methyl esters determined by IR, with methyl elaidate as the external standard, was correlated to the capillary GLC weight percentages of the componenttrans fatty acid methyl esters by the mathematical formula: IRtrans=%18∶1t+0.84×%18.2t+1.74×%18∶2tt+ 0.84×%18∶3t where 0.84, 1.74 and 0.84 are the correction factors which relate the GLC weight percentages to the IRtrans‐equivalents for mono‐trans‐octadecadienoic (18∶2t),trans, trans‐octadecadienoic (18∶2tt) and mono‐trans‐octadecatrienoic (18∶3t) acids, respectively. This formula forms the basis for the determination of totaltrans‐andcis‐octadecenoic acids in partially hydrogenated vegetable oils. From the weight percentages of 18∶2t, 18∶2tt and 18∶3t determined by capillary GLC on a cyanosilicone liquid phase and the totaltrans‐unsaturation by IR, the percentage of the totaltrans‐octadecenoic acids (18∶1t) is calculated using the formula. The difference between the total octadecenoic acids (18∶1), determined by capillary GLC, and the 18∶1t gives the totalcis‐octadecenoic acids.
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