Chromatographic separation of chlorthalidone enantiomers using beta-cyclodextrins as chiral additives

Different beta-cyclodextrins have been tested as chiral additives in the mo bile phase for the chromatographic analysis of chlorthalidone enantiomers i n a C-18 LiChrospher (125x4 mm I.D.) column. The effect on enantioresolutio n of different parameters was studied: composition of the mobile phase (per centage of organic solvent, type of buffer and pH), mobile phase flow-rate, and type and concentration of beta-cyclodextrin. A 25:75 mixture of methan ol and 0.1 M phosphate buffer, pH 4, containing 2% triethylamine (v/v), and 12.5 mM beta-cyclodextrin, at a flow-rate of 0.8 ml/min, was found to be t he best option for the resolution of chlorthalidone enantiomers. Under such conditions, linear calibration curves were obtained in the 0.5-20-mu g/ml interval using UV detection at 230 nm. The limit of detection for both isom ers was 50 ng/ml. The utility of the described assay has been tested by ana lyzing chlorthalidone in different pharmaceutical preparations. Examples of application to biological samples are also given. (C) 2000 Elsevier Scienc e B.V. All rights reserved.