[Simultaneous determination of levodopa and methyldopa in human serum by capillary electrophoresis]

A simple capillary electrophoresis method was developed for the determination of levodopa and methyldopa in human serum. The effects of pH and concentration of buffer, voltage and injection time on separation were investigated. As a result, an optimized separation was obtained with a fused-silica capillary of 60.2 cm (50 cm effective length) x 75 microm i. d. in a running buffer of 40 mmol/L sodium tetraborate (pH 9.5) with an applied voltage of 22 kV at 25 degrees C. Sample introduction was performed at 3.45 kPa (0.5 psi) for 7 s and on-column detection was made with a diode array detector at 200 nm. The linear responses covered the ranges from 1.0 to 64.0 mg/L (r = 0.999 8) for methyldopa and from 1.0 to 71.0 mg/L (r = 0.999 4) for levodopa. The detection limits (S/N = 3) of methyldopa and levodopa were shown to be 0.6 mg/L and 0.8 mg/L, respectively. The recoveries for levodopa and methyldopa in human serum were between 82.8% and 88.8% with relative standard deviations between 2.10% and 2.63%.