The glassy carbon working disc electrode was placed opposite the channel outlet; the distance between the electrode surface and the channel outlet was controlled by the screw. The electrochemical detection compartment was filled with 10 mM phosphate buffer (pH 8). The electropherograms were recorded with a time resolution of 0.1 s and a detection potential of (+1.1 V versus Ag/AgCl wire). Sample injections were performed after the baseline stabilization. All experiments were done at room temperature.