SILVER ION HIGH PERFORMANCE LIQUID CHROMATOGRAPHY OF POLYNUCLEAR AROMATIC DERIVATIVES OF POSITIONALLY ISOMERIC OCTADECENOIC FATTY ACIDS

Abstract

The chromatographic properties of positionally isomeric octadecenoic fatty acids in silver ion high performance liquid chromatography with hexane-based and dichloromethane-based mobile phases were studied after conversion in 2-naphthacyl, 2-naphthylmethyl and 9-anthrylmethyl derivatives. The retention decreased in the order 2-naphthacyl, 9-anthrylmethyl, 2-naphthylmethyl derivatives. Dichloromethane-acetonitrile mobile phases provided better resolution and 2-naphthacyl and 9-anthrylmethyl derivatives of 6-, 9-, and 11–18:1 were fully resolved with dichloromethane-acetonitrile 100:0.025 (v/v). The behavior of the aromatic derivatives, examined so far by Ag-HPLC, under comparable experimental conditions, was compared and a clear tendency of improving the resolution was observed when the number of aromatic nuclei in the aromatic fragment increased. The effect was ascribed to the increased electron-donating effect of the aromatic rings in the ester moiety, which supposedly enhanced the formation of a three center complex between double bond, a carbonyl oxygen, and silver ion. The good resolution of 9-anthrylmethyl derivatives is of potential practical value since it allows for the determination of nanogram amounts of fatty acids by silver ion HPLC with fluorescent detection.