Determination of thiazinamium, promazine and promethazine in pharmaceutical formulations using a CZE method

We present the validation of a developed method using capillary zone electrophoresis (CZE) for quantitative analysis of three phenothiazines: thiazinamium methylsulphate (TMS), promazine hydrochloride (PMH) and promethazine hydrochloride (PTH) in pharmaceutical formulations. The influence of various parameters affecting the CZE separation (buffer pH and concentration, acetonitrile percentage, capillary temperature and applied voltage) was investigated by means of multivariate optimization using experimental designs so as to obtain the highest efficiency. The method allows the separation of the phenothiazines in 5.0 min at optimized conditions: 100 mM tris(hydroxymethyl)-aminomethane (Tris) buffer at a pH 8.0, 15% acetonitrile, capillary with 58.5 cm in length at 25 °C and a voltage of 30 kV. Detection occurred at 254 nm. Acceptable precision (relative standard deviation (R.S.D.) 5.3%) and linearity were achieved using the internal standard (IS) method. The limits of detection (LODs) were 2.8 μg ml−1 for TMS and 3.3 μg ml−1 for PMH and PTH. The method has been successfully applied in the analysis of pharmaceutical formulations.