Enrichment of chlorthalidone enantiomers by an aqueous bulk liquid membrane containing beta-cyclodextrin

A single (one membrane and one strip phase) and a multiple (three membranes and three strip phases) bulk liquid membrane (BLM) containing P-cyclodextr in (CD) as chiral mobile carrier was used for the chiral enrichment of race mic chlorthalidone (CT). Initial solubility and partitioning data of CT in ethylacetate (EtOAc) (feed and strip phase) and in water (membrane phase) g ave a distribution coefficient (K-d = [CT](aq)/[CT](ETOAc)) of 0.04 and a D elta G for complexation of +7.8 kJ mol(-1). The influence of both PH and ca rrier concentration on BLM enrichment was evaluated. In spite of the small Kd and positive Delta G, chiral enrichment was feasible and the highest sel ectivity (alpha = 1.41) was obtained with the multiple BLM at low pH (pH = 5) and low relative carrier concentration (CD : CT ratio = 1 :4), The low p H reduced solubility and thus passive transport of CT in the membrane phase . Both the improvement of selectivity at lower [CD] and the fact that the h ighest selectivity under all conditions was during the initial stages of th e membrane process, illustrated that complexation was kinetically driven. ( C) 2000 Elsevier Science B.V. All rights reserved.