Comparison of the Chromatographic Retention in Octadecyl- Bonded Silica/(Methanol-Water) System with Partition Coefficient in Dodecane/(Methanol-Water) System

Abstract

Liquid chromatographic capacity factors (k′) were measured for thirty two compounds including alkanes, aromatic hydrocarbons, esters, ketones and alcohols in an octadecyl bonded silica gel (ODS)/(methanol-water) system. The k′ of each compound was compared with the partition coefficient (P) in the liquid-liquid system consisting of dodecane and the methanol-water of a composition identical to that used in the chromatography (the molar fraction of methanol in the mixture, 0.4-1.0). A ratio, k′/P, increased with decrease in P. The k′/P ratio of a relatively polar compound was noticeably affected by the composition of methanol-water. The energy difference in the solute-solvent interactions occurring in the methanol-water phase and in the dodecane phase was estimated using the scaled particle theory. It was found that the more strongly a solute interacted with a polar solvent, such as methanol and/or water, than a nonpolar solvent such as dodecane, the more easily the solute transfer tended to occur from the polar phase to the ODS phase rather than to the dodecane phase.