A sensitive voltammetric method has been developed for the determination of noscapin and leucine on glassy-carbon electrode modified by multiwalled carbon nanotubes. The method was based on catalytic effect of multiwalled carbon nanotube as a hetrogeneous catalyst on the oxidation of the noscapine and leucine on the surface of a modified glassy carbon electrode. Cyclic voltammtery method was used for determination of the species and result has shown that peak current is dependent on concentration of them. The effect of pH and scan rate on the sensitivity were studied. Optimum pH values for voltammetric determination of noscapine and leucine were 6.0 and 10, respectively. Under the optimized conditions the calibration curves were linear in the concentration range of 0.1-100.0and 10.0-1500.0 µM for noscapine and leucine, respectively and relative standard deviation of methodes were lower than 1% and near one for noscapine and leucine respectively. The detection limit (signal to nise equal to 3) were 0.08, and 0.40 µM for first and second anodic noscapine peak and 3.0 to 5.0 µM for variouse leucine peak, respectively. Performance of methodes was estimated by determination of noscapine and leucine contents in plasma, urine and multi drug as real sample with satisfactory results. The electrone transfer number and diffusion coefficient of noscapine and leucine were calculated and mechanism for multistep oxidation of noscapine and leucine were proposed.
