GLC and TLC analysis of isopropylidene derivatives of isomeric polyhydroxy acids derived from positional and geometrical isomers of unsaturated fatty acids

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Abstract
Gas-liquid chromatography (GLC) and thin-layer chromatography (TLC) were used to investigate the isomeric positional geometrical isopropylidene derivatives of nine isomeric dihydroxy esters, four isomeric methyl 9,10-12-trihydroxystearates, and eight isomeric methyl 9,10-12,13-tetrahydroxystearates prepared from unsaturated fatty acids. The isopropylidenes derived fromcis andtrans monounsaturated fatty acids were easily separated on both polar and nonpolar columns. Positional isopropylidenes derived from positional isomers of monounsaturated fatty acids were not separated on either liquid phase but were resolved by TLC. Four of the eight isomeric isopropylidenes derived from the four geometrical isomers of linoleic acid were resolved on the polar column; the other four isomers eluted as a single peak. The four isomeric isopropylidene-trifluoroacetate derivatives derived from ricinoleic and ricinelaidic acids were also resolved on the polar column. GLC analyses were carried out with liquid phases of ethylene glycol succinate methyl silicone polymer (EGSS-X) and methyl silicone polymer (SE-30) packed columns. Isopropylidenes, in addition to their applicability for the resolution of polyhydroxy acid mixtures, are particularly useful for the determination of double bond positions and geometrical configurations of fatty acids without cleavage.