Determination of Levodopa and Benserazide Hydrochloride in Pharmaceutical Formulations by CZE with Amperometric Detection

A novel method, capillary electrophoresis with amperometric detection, has been established for rapid and effective measurement of levodopa (L-dopa), and benserazide (BS) and its impurity (R,S)-2-amino-3-hydroxypropanohydrazide (Ro-04-1419) in co-beneldopa pharmaceutical formulations. Suitable separation and amperometric detection conditions were investigated and optimized. The optimum conditions of CZE detection were 40 mm phosphate solution at pH 5.3 as running buffer, 17 kV separation voltage, carbon-disk working electrode, 0.95 V (relative to Ag/AgCl) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 1.25 to 50 g mL^–1 for L-dopa, 1.2 × 10^–1 to 25.5 g mL^–1 for BS, and 1.0 × 10^–2 to 4.4 × 10^–1 g mL^–1 for Ro-04-1419, with correlation coefficients of 0.9994, 0.9951, and 0.9933, respectively. The detection limits for L-dopa, BS, and Ro-04-1419 were 0.38, 0.02, and 0.004 g mL^–1, respectively. Average recoveries were 100.2% for L-dopa, 102.4% for BS, and 90.8% for Ro-04-1419. This method was successfully applied to co-beneldopa granules and tablets.Revised: 30 November and 22 December 2004