Analysis of optical purity and impurity of synthetic d‐phenylalanine products using sulfated β‐cyclodextrin as chiral selector by reversed‐polarity capillary electrophoresis

Abstract

A new capillary electrophoresis (CE) method has been achieved for simultaneous separation and quantification of phenylalanine, N-acetylphenylalanine enantiomers, and prochiral N-acetylaminocinnamic acid, possibly co-existent in reaction systems or synthesized products of D-phenylalanine. The separation was carried out in an uncoated capillary under reversed-electrophoretic mode. Among the diverse charged cyclodextrins (CDs) examined, highly sulfated (HS)-beta-CD as the chiral selector exhibited the best enantioselectivity. The complete separation of the analytes was obtained under the optimum conditions of pH 2.5, 35 mM Tris buffer containing 4% HS-beta-CD, applied voltage -15 kV, and capillary temperature 25 degrees C. Furthermore, the proposed method was applied to the determination of optical purity and trace impurities in three batches of the asymmetric synthetic samples of D-phenylalanine, and satisfactory results were obtained. The determination recoveries of the samples were in the range of 97.8-103.8%, and precisions fell within 2.3-5.0% (RSD). The results demonstrate that this CE method is a useful, simple technique and is applicable to purity assays of D-phenylalanine.