Analysis of steroids by nonaqueous capillary electrophoresis

A simple method for the separation and determination of steroids (estradiol valerate, triamcinolone, levonorgestrel and ethinylestradiol) in single and compound tablets by nonaqueous capillary electrophoresis with ultraviolet (UV) spectrophotometric detection has been developed for the first time. After optimizing the electrophoretic parameters, including the nature of electrolytes and composition of organic solvent, the running buffers of methanol-acetonitrile (95: 5, v/v) containing 20 mM sodium acetate (pH 6.5) and methanol-acetonitrile (90: 10, v/v) containing 25 mM sodium acetate (pH 7.0) were found to be most suitable for determining estradiol valerate and triamcinolone, respectively. Reliable separation and simultaneous determination of levonorgestrel and ethinylestradiol were achieved in methanol containing 20 mM of ammonium acetate and 10 mM of sodium dodecyl sulfate (SDS). Tamoxifen was used as internal standard. Performance of the method, including migration time and peak area reproducibility, linearity, sensitivity and accuracy, were also evaluated. The limits of detection (S/N = 3) for four analytes were in the range of 9.8–19.5 μ g/mL. The relative standard deviations (RSD) of the migration times and peak areas of the analytes were in the range of 0.14–1.0% and 0.7–2.7% (intraday), 0.5–2.8% and 1.5–4.2% (interday), respectively. Within the tested concentration range, linear relationships between peak area ratios and concentrations of the analytes were obtained (correlation coefficients: 0.9987–0.9996). The method has been successfully applied to the determination of ingredients with recoveries over the range of 96.6–100.6%.