Capillary electrophoretic enantioselective determination of zopiclone and its impurities

A capillary electrophoretic enantioselective method with UV detection was developed and validated for the simultaneous quantification of zopiclone enantiomers and its impurities, zopiclone-N-oxide enantiomers, and 2-amino-5-chloropyridine, in tablets. The analytes were extracted from the tablets using ACN and were separated in an uncoated fused-silica capillary (50 μm, 42 cm effective length, 50 cm total length) using 80 mM sodium phosphate buffer pH 2.5 and 5 mM carboxymethyl-β-cyclodextrin as running buffer. The analytes and the internal standard (trimethoprim) were detected at 305 and 200 nm, respectively. A voltage of 27 kV was applied and the capillary temperature was maintained at 25°C. All enantiomers were analyzed within 8 min and linear calibration curves over the concentration range of 0.4-0.8 mg mL⁻¹ for each zopiclone enantiomer, 0.8-1.6 μg mL⁻¹ for 2-amino-5-chloropyridine and 0.4-0.8 μg mL⁻¹ for each zopiclone-N-oxide enantiomer were obtained. The coefficients of correlation obtained for the linear curves were greater than 0.99. The intra-day and inter-day accuracy and precision were lower than 2% for all analytes. This validated method was employed to study the degradation and racemization of zopiclone under stress conditions. This application demonstrated the importance of a stability-indicating assay method for this drug.