The HPLC-electrochemical measurement using a BDD electrode as an amperometric detector was carried out in the mobile phase (1:1 (v/v) ratio of acetonitrile:0.05M phosphate solution, which was adjusted to pH 2.5 with phosphoric acid) with an applied
potential of 1.05V vs. Ag/AgCl and a flow rate of 1.0 mL/min.The HPLC system consisted of an HPLC compact pump model 2250 (Bischoff, Germany), a 20L sample loop injection (Rheodyne No. 7125, USA), a thin-layer flow cell (GL Sciences, Inc.),an amperometric detector and a data acquisition system (Ecochemie Netherland). The chromatographic column was a Luna 5u C18 column (150mm×4.6mm i.d.) from Phenomenex and all
chromatographic separations were performed at room temperature (∼25 ◦C). The amperometric determination was performed after obtaining the hydrodynamic voltammogram. The peak current after each injectionwasrecorded along with the corresponding
background current. These data were plotted as a function of applied potential to obtain the hydrodynamic voltammograms. The amperometric measurements were carried out at the potential that provided the maximum signal-to-background (S/B) ratio in the hydrodynamic voltammograms.