DETERMINATION OF TRANS-FATTY-ACIDS IN HYDROGENATED VEGETABLE-OILS BY ATTENUATED TOTAL-REFLECTION INFRARED-SPECTROSCOPY - 2 LIMITED COLLABORATIVE STUDIES

An attenuated total reflection infrared spectroscopy procedure was col laboratively studied among two sets of five laboratories for quantitat ing the total trans fatty acid levels in neat (without solvent) hydrog enated vegetable oils, measured as triacylglycerols in one study, and as fatty acid methyl ester derivatives in the other. Unlike the fatty acid methyl esters, the triacylglycerols required no derivatization bu t had to be melted prior to measurement. To obtain a symmetric absorpt ion band at 966 cm(-1) on a horizontal background, the single-beam spe ctrum of the trans-containing fat was ''ratioed'' against that of a re fined oil or a reference material that contained only cis double bonds . A single-bounce horizontal attenuated total reflection cell that req uires 50 mu L of undiluted test samples was used for oils, melted fats , or their methyl esters. For fatty acid methyl esters, the reproducib ility relative standard deviations were in the range of 0.9 to 18.46% for 39.08 to 3.41% trans, determined as methyl elaidate per total fatt y acid methyl esters. For five pairs of triacylglycerol blind duplicat es, the reproducibility and repeatability relative standard deviations were in the ranges of 1.62 to 18.97%, and 1.52 to 13.26%, respectivel y, for 39.12 to 1.95% trans, determined as trielaidin per total triacy lglycerols. Six pairs of spiked triacylglycerol blind duplicates (qual ity assurance standards) exhibited high accuracy in the range of 0.53 to 40.69% trans and averaged a low bias of 1.3%. These statistical ana lysis results were compared to those collaboratively obtained by the r ecently adopted AOCS Cd14-95 and AOAC 994.34 Infrared Official Methods .