Study of the retention properties of warfarin enantiomers on a beta-cyclodextrin polymeric support

High-performance liquid chromatography was used to study the retention prop erties of (R)- and (S)-warfarins on a silica support coated with a beta -cy clodextrin polymer. The influence of the methanol content of the acetate bu ffer eluent was investigated at pH 4. The measure of the variations of rete ntion time with temperature enables one to determine the enthalpy and the e ntropy of adsorption. The plot of the two thermodynamic functions shows a m inimum around 30% (v/v) methanol. At low methanol contents, the decrease of the hydrophobic interactions with increasing methanol content explains the decrease of the enthalpic and entropic terms. Above 40% (v/v) methanol, th e decrease of the adsorption enthalpy absolute value is due to the solvatio n by the organic component. From the analysis of peak shape in mass-overloa d conditions, the column capacity toward each enantiomer was determined. A lower capacity was found toward (S)-warfarin, the more retained enantiomer. Peak shape analysis in mass-overload conditions was used to determine the adsorption isotherm. A Langmuir-type adsorption isotherm accounts well for the experimental data. (C) 2001 Elsevier Science B.V. All rights reserved.