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Abstract:
Enatioselective chromatography on chiral stationary phase has become integral part of drug research, development and production on the industrial scale. Development of new highly selective stationary phases and effective techniques of chromatographic separation such as SMB or Varicol processes resulted in increasing interest in chromatographic process as an effective separation method. Due to high cost of chiral stationary phases chromatographic separation should be conducted under conditions guaranteeing the highest process performance. An important operating variable is composition of the mobile phase, which has crucial influence on the selectivity of separation. Hence, type and concentration of active components of the mobile phase should be properly selected and their effect on the process performance should be quantified.
In this work adsorption of the mobile phase has been investigated on Chirobiotic-T stationary phase. Binary mixtures of polar solvents allowing enantioseparation of amino acid, D and L threonine, have been considered. Absorption equilibria of three different systems of binary water-alcohol mixtures have been examined: water mixed with methanol, ethanol or propan-2-ol. The excess adsorption of the alcohols have been measured and isotherm equations have been quantified. Strongly nonideal behavior of solvents in both the mobile and the stationary phases has been identified and accounted for by the activity coefficients. The Margules or van-Laar equations for water-alcohol mixtures reported in literature have been exploited to quantify nonideality of the mobile phase. Activity coefficients in the adsorbed phase have been determined by fitting the simulations to the experimental data of the excess adsorption.
In the next stage adsorption equilibria of isomers of threonine have been determined at different alcohol contents in the mobile phase. The heterogeneous mechanism of adsorption has been identified and was approximated by bi-Langmuir isotherms. The results obtained for all three systems have been compared. Strong influence of adsorption of alcohols on the retention behavior of the solutes have been evidenced and analyzed. The results obtained will be presented and discussed.
