isomer Separation by Reversed-phase Liquid Chromatography Using 2-(1-Pyrenyl) ethyl Stationary Phase Separation of Unsaturated Compounds

Abstract

Separations of positional isomers and geometrical isomers of unsaturated compounds were examined by using octadecylsilylated (C₁₈) phase and 2-(1-pyrenyl)ethylsilylated (PYE)phase on silica gel in reversed-phase liquid chromatography.
C₁₈ phase showed preferential retention of solutes with double bonds at an internal position and with E configuration. The results can be explained in terms of the hydrophobic property of each solute. The interaction between double bonds in a solute and pyrene rings of PYE phase contributed to the unique selectivity of this stationary phase. Stronger interactions were observed with a double bond at a terminal position and with an internal double bond with Z configuration. The tendency can be explained by the steric effect of substituents on the sp² carbon atoms. The electronic interaction was pronounced in a mobile phase of high methanol contents, because of the smaller contribution of hydrophobic interaction in such a mobile phase. In the case of unsaturated carboxylic acid derivatives, PYE phase showed preferential retention for solutes possessing double bonds away from the carboxyl group, and provided separation between linolenic acid and γ-linolenic acid, which cannot be separated by C₁₈ phase.
The complementary use of PYE phase, which has widely different selectivity, with C₁₈phase will increase the capability of reversed-phase liquid chromatography.