Hydrogenation of soybean oil: a thin-layer chromatography and gas chromatography/matrix isolation/Fourier transform infrared study

By use of gas chromatography/matrix isolation/Fourier transform infrared (GC/MI/FT-IR) spectroscopy, the double-bond configurations of fatty acid methyl esters (FAMEs) derived from hydrogenated soybean oil and margarine were determined from the positions of observed IR bands. However, because of the formation of complex FAME mixtures with overlapping GC peaks, preliminary separation was necessary. Mixtures of FAMEs were separated by silver nitrate thin-layer chromatography and GC using a polar cyanopropylpolysiloxane capillary column. GC eluates were trapped at 12 K under high vacuum in an argon matrix and subsequently analyzed by IR spectroscopy. Because of the high specificity of the MI/FT-IR technique, unique IR spectra were obtained that allowed the characterization of eight C18 diene FAME positional isomers with trans, trans or trans/cis configuration. C18 FAMEs with identical GC retention times were readily distinguished, and their degree of unsaturation and double-bond configuration were established by IR spectroscopy.