Qualitative and quantitative determination of the cis and trans fatty-acid content of fats and oils using FTIR.
The aim of this work was to assess the potential of FTIR spectroscopy in the analysis of the cis
and trans fatty acid contents of fats and oils.
Preliminary studies on the liquid and solution phase spectra of individual FAME's (fatty acid
methyl esters), and on mixtures of FAME's, were conducted to establish whether spectral
features enhanced by FTIR could be used to provide improved methods of determining cis
and trans contents.
A number of previously unreported bands and spectral features associated with the cis and
trans isolated double bond(s) were discovered. None of the trans bands were considered
suitable for quantitation, however. methods of determining the cis content were developed.
based on the the two bands listed below. These methods were compared with current IR
methods. and with a capillary GC method.
(a) The cis C=C stretching band (= 1654 em-1).
(b) An unassigned band at .. 913 cm-1. observed only in the spectra of non-conjugated diand
All the established methods as well as those developed in this work. for the quantitative
analysis of FAME's have inherent disadvantages. For example. with the capillary GC method.
difficulties are encountered in resolving and identifying samples containing complex mixtures
of isomers. With the IR techniques. the difficulties involve the elimination of interfering bands.
and the absorbance of similar fatty acids at the same frequencies.
The application of GC-FTIR was seen as a logical extension of this project. because it offered a
great potential for the separation and charactisation of components of complex mixtures.
Studies conducted on vapour phase spectra showed that the identification of many FAME's
could be ascertained from various band ratios. Furthermore. band ratios could be used to
quantify the cisltrans content of co-eluting isomers. Different types of capillary columns were
tried. and optimum conditions established where possible.