SPECTRAL CONFIRMATION OF TRANS MONOUNSATURATED C-18 FATTY-ACID POSITIONAL ISOMERS

The trans octadecenoic acid methyl ester isomers were obtained from a partially hydrogenated soybean oil sample and isolated by silver-ion h igh-performance liquid chromatography. The double bond configuration w as confirmed to be trans by using gas chromatography-direct deposition -fourier transform infrared spectroscopy. The double bond positions fo r nine individual trans octadecenoic acid positional isomers were conf irmed by gas chromatography-electron ionization mass spectrometry afte r derivatization to 2-alkenyl-4,4-dimethyloxazoline. These nine trans positional isomers were resolved on either one of the two polar 100% c yanopropylpolysiloxane 100-m capillary columns, SP 2560 and Cp-Sil 88, at an isothermal temperature of 140 degrees C. These nine isomers wer e confirmed to have double bonds at carbons C-8 through C-16. The pair of trans octadecenoic acid positional isomers with double bonds at C- 13 and C-14 are reported for the first time to be resolved by gas chro matography.