Determination of rufinamide, lamotrigine, and zonisamide by capillary electrophoresis

In this study, a simple, rapid, and sensitive capillary electrophoresis (CE) method was developed for the simultaneous determination of rufinamide (RFN), lamotrigine (LMT), and zonisamide (ZNS). The method was compared to a High-Performance Liquid Chromatography (HPLC) method. CE analysis was performed using a photodiode array detector (DAD) at 210 nm, employing a capillary with a 75 µm internal diameter and a 40 cm effective length. Optimal separation was achieved by using a background electrolyte consisting of 35 mM SDS, 6 mM borate, 10 mM phosphate buffer (pH 9.00), and 5% isopropyl alcohol (IPA), with an applied potential of 15 kV. Under these conditions, the migration times for ZNS, RFN, and LMT were found to be 5.99, 6.77, and 8.46 minutes, respectively. In the HPLC method, detection was also conducted at 210 nm using a C18 column (4.6×100 mm, 3.5 µm) and a mobile phase of 18% acetonitrile and 50 mM phosphate buffer (pH 4.0) at a flow rate of 1.0 mL/min. The retention times for ZNS, RFN, and LMT were 6.41, 7.29, and 4.95 minutes, respectively. Both methods were validated for parameters such as linearity, precision, sensitivity, stability, and robustness. The limits of detection (LOD) in the CE method for ZNS, RFN, and LMT were 1.63×10⁻⁷ M (0.035 μg/mL), 6.86×10⁻⁸ M (0.016 μg/mL), and 2.65×10⁻⁸ M (0.007 μg/mL), respectively. For HPLC, the LOD values were 1.61×10⁻⁸ M (0.003 μg/mL) for ZNS, 9.69×10⁻⁹ M (0.002 μg/mL) for RFN, and 3.33×10⁻⁹ M (0.001 μg/mL) for LMT. Both methods were successfully applied to pharmaceutical formulations and were compliant with USP 47-NF 42 standards.