Interactions between native cyclodextrins and n-alcohols studied using thermostated thin-layer chromatography

Abstract

Using thermostated thin-layer chromatography, the retention behavior of α-, β- and γ-cyclodextrin on a C 18 stationary phase was studied. As mobile phases, a homologous series of n-alcohols, from ethanol to pentanol, and their mixtures with water were examined. Chromatographic experiments were performed either at a constant temperature (30°C) and over a wide range of binary mixtures (0–100%, v/v), for ethanol and propanol, as well as at fixed mobile phase composition and different temperatures from 5°C to 60°C. Using isoelution binary mobile phases, the effect of temperature on retention of cyclodextrins was examined. Results were compared with chromatographic retention data from previously reported work in which methanol–water binary phases were used. From linear Van ‘t Hoff plots thermodynamic parameters such as the change of enthalpy (Δ H 0) and the change of entropy (Δ S 0) were estimated. In each case the sign of the calculated parameters is negative. Nonlinearities of Van ‘t Hoff plots were observed when propanol or butanol was used as a component of binary mobile phase.