The nitrogen-doped carbon nanotube (CN_x nanotube) modified glassy carbon elec-trodes were prepared for the study of electrochemical behavior of dopamine (DA) and ascorbic acid (AA). The effects of the content of nitrogen in the framework of CN_x nanotubes on the electrochemical behavior of DA and AA at the modified glassy carbon electrodes were investigated in acidic and neutral buffer solutions. The results of cyclic voltammetry indicated that the CN_x nanotube modified electrodes with a high content of nitrogen exhibited higher electrocatalytic activities for the AA, the modified electrodes with a low content of nitrogen, however, showed the favorable electrocatalytic activity for DA. Additionally, the modified electrodes showed a linear response to DA in the concentration range of 5.0×10^－6～2.0×10^－4 mol/L and AA in the concentration range of 3.0×10^－5～1.0×10^－2 mol/L. The detection limit (S/N＝3) is 1.64×10^－6 mol/L for DA and 3.26×10^－6 mol/L for AA, respectively. Such different catalytic behavior for DA and AA allowed the determination of DA in the presence of extremely excess AA (up to 20000 fold).

Key words: nitrogen-doped carbon nanotube, modified electrode, dopamine, ascorbic acid