GAS-CHROMATOGRAPHIC MATRIX-ISOLATION FOURIER-TRANSFORM INFRARED SPECTROSCOPIC DETERMINATION OF TRANS-MONOUNSATURATED AND SATURATED FATTY-ACID METHYL-ESTERS IN PARTIALLY HYDROGENATED MENHADEN OIL

Elaidic acid (t-18:1) has been the focus of a literature debate about its effect on blood cholesterol levels. A method is presented that can accurately quantify the level of t-18:1, a single geometric isomer, i n hydrogenated menhaden oil. Fatty acid methyl esters (FAMEs) were det ermined by Fourier transform infrared spectroscopy. The t-18:1 FAME an d related trans-monounsaturated and saturated compounds were quantitat ed by linear regression analysis from the intensities of the 971- and 1121-cm-1 infrared bands, respectively. The 971-cm-1 band is produced for trans geometric isomers only; thus, interference from cis isomers, due to GC peak overlap, is eliminated. At an iodine value of 78, the t-18:1 composition of hydrogenated menhaden oil was 2.6% by weight. Th e use of internal standards was essential for quantitation. Satisfacto ry repeatability was achieved for quantitation of FAMEs from duplicate high-performance liquid chromatographic fractions; the t-18:1 FAME we ight percent varied by 7.4%.