Analysis of vancomycin and related impurities by micellar electrokinetic capillary chromatography. Method development and validation

A fast and highly selective micellar electrokinetic capillary chromatograph y (MEKC) method for quantitative analysis of vancomycin and related impurit ies is described. Among the tested surfactants, cetyltrimethylammonium chlo ride (CTAC) offered the best selectivity. Another important parameter, whic h strongly influenced the selectivity, was buffer pH. It was found that the selectivity increased with buffer pH decreasing from 9 to 5. Using Tris-ph osphate buffer containing CTAC, satisfactory separation could be obtained i n the pH range from 5.0 to 5.5. Excellent repeatability in terms of migrati on time and peak area could be obtained when the capillary was carefully wa shed between two runs. In order to obtain optimal conditions and to evaluat e the method robustness, a central composite experimental design was carrie d out. The optimal conditions were: 44 cm length of fused-silica capillary with 50 mum ID, 120 mM Tris-phosphate buffer (pH 5.2) containing 50 mm CTAC , -15 kV applied voltage, UV detection at 210 nm, and a column temperature of 25 degreesC. Under the optimal conditions, more than 20 peaks could be s eparated within 8 min. The method has a linearity range from 0.004 to 1.2 m g/ml (concentration of vancomycin B, active component). The limit of detect ion (LOD) and limit of quantitation (LOO) were 0.4 mug/mL vancomycin, equiv alent to 0.3 mug/mL vancomycin B (0.04%) and 1.1 mug/mL vancomycin, equival ent to 0.9 mug/mL vancomycin B (0.1%), respectively.