Retention in reversed-phase liquid chromatography: solvatochromic investigation of homologous alcohol-water binary mobile phases

Abstract

The mechanism of retention in reversed-phase liquid chromatography (RPLC) has been further investigated using the E T(30) solvatochromic solvent polarity scale. The retention behavior of a variety of solutes was measured using a homologous series of normal alcohols as the organic modifiers in hydroorganic mobile phases. The results imply that a systematic change in the extent of solvation of the stationary phase occurs with respect to the size of the organic modifier. It was also found that a linear extrapolation of the log k′ versus E T(30) plots for different mobile phases using methanol, ethanol and acetonitrile (but not n-propanol) as modifiers, intersected at approximately the E T(30) value of pure water. This intersection is further evidence that the E T(30) model of solute retention is a useful tool with which to study the mechanism of retention in RPLC. The extrapolated retention value in water, log k′ w, from the E T(30) plots should then prove to be a more reliable means of estimating solute lipophilicity using RPLC than the percent organic modifier model.