Silver ion high-performance liquid chromatography of isomeric cis- and trans-octadecenoic acids -: Effect of the ester moiety and mobile phase composition

The effects of the ester moiety and of the mobile phase composition on the resolution of cis and trans positional isomers of octadecenoates have been studied by silver ion HPLC with UV detection. The efficiency of the separation increases in the order phenethyl<phenacyl<p-methoxyphenacyl esters. Retention and resolution are substantially affected by small changes in the proportion of acetonitrile in the mobile phase. Dichloromethane influences retention but has a small effect on resolution. Clear resolution of cis and trans positional isomers of octadecenoic acid in partially hydrogenated sunflower oil has been achieved after conversion into p-methoxyphenacyl esters on a silver ion column by isocratic elution with a mobile phase of hexane-dichloromethane-acetonitrile (60:40:0.2, v/v) in only 22 min. (C) 1998 Elsevier Science B.V.