Chiral separation of tramadol enantiomers by capillary electrophoresis using cyclodextrins as chiral selectors and experimental design method optimization

Tramadol is a centrally acting analgesic drug, used in therapy as a racemic mixture of its trans enantiomers: (1R,2R) and (1S,2S). A simple capillary electrophoresis (CE) method was developed for the chiral separation of tramadol enantiomers using carboxymethyl-β-CD (CM- β-CD) as chiral selector. Influence of buffer pH and concentration, CD concentration, capillary temperature, applied voltage and injection parameters on the chiral separation was evaluated. Optimization of the analytical conditions was performed using a preliminary “one factor at time” approach followed by a faced-centred central composite design. The best results were obtained when using 25 mM sodium tetraborate buffer at pH 11.0, 5 mM CM-β-CD as chiral selector, + 17.5 kV voltage, 15 °C temperature, and 30 mbar/1 s hydrodynamic injection. The analytical performance of the method was evaluated in terms of precision, linearity, accuracy, detectability and robustness. The method was applied successfully for the determination of tramadol enantiomers from pharmaceutical formulations.