The paper discusses the methods of determination of the position of unsaturated bonds in a chain of acids, the determination of the sum of conjugated unsaturated bonds and the composition of the fatty acids. The position of unsaturated bonds in acids of modified oils may be determined most quickly by the method of pyrrolidide derivatives and determinations by the GLC-MS method. The content of conjugated bonds had been determined by standardized method of UV spectrometry, and the composition of the fatty acids had been determined by gas chromatography.
D e t e r m i n a t i o n of P o s i t i o n I s o m e r s
Determination of the position of unsaturated bonds in fatty acids containing one or several unsaturated bonds in a molecule, is one of the more difficult problems from the analytical point of view, even if one deals with mixtures of acids or their esters with the same number of carbons in the chain, particularly if the molecular weights exhibit significant differences. For such systems there is practically no direct and quick analytic method.
Already in 1959, Heino Susi reported' that by the IR spectroscopy it is possible to determine the position of an unsaturated bond in the carbon chain, by investigating the absorption zone in the 1180-1850 cm ' range. The number of bands in this range is connected with the length ofthechain. Forlonger chains, the number of bands corresponds to a half of the number of carbons in the chain (from the last carboxyl group to the unsaturated bond). This method may be used only for esters of individual fatty acids, and therefore it is not widely utilized.
Some position isomers of fatty acids may be determined in their methyl esters by chromatographic methods. As it was mentioned', the attempts to separate position isomers of octadecane acids by means of argentic thin layer chromatography yielded according Lit.' good results, provided that the silicagel was saturated with 30% AgNO,,and with triple development with toluene in a temperature of -25O C. The following differences in the values of Rf had been obtained: