Simultaneous determination of levodopa and its metabolite in human blood by capillary electrophoresis with laser-induced fluorescence detection

A rapid, sensitive and reproducible method is described for the analysis of levodopa and its metabolite dopamine (DA) in human blood. The influence of carbidopa as the inhibitor againist the decarboxylase activity on the metabolism has been also studied. After derivatization in a dark pulsator for 12 h at room temperature, the fluorescein isothiocyanate (FITC) derivative of levodopa and other components were separated by capillary zone electrophoresis (CZE) within 13 min and detected with laser-induced fluorescence (LIF). Under the optimum analysis conditions, the linear range is 3.0 x 10(-8)-4.0 x 10(-6) mol/L and 1.0 x 10(-8)-2.0 x 10(-6) mol/L for levodopa and DA, respectively. The detection limits of levodopa and DA were 7.8 x 10(-9) mol/L (39.0 amol) and 3.1 x 10(-9) mol/L (15.5 amol), respectively. The method was successfully applied to monitoring the levodopa and DA in human blood after one took tablets orally.