Selective determination of catechol in the presence of hydroquinone at bare indium tin oxide electrodes via peak-potential separation and redox cycling by hydrazine

The electrochemical, selective determination of catechol (CT) in the presence of hydroquinone (HQ) is not readily achieved, because the formal potentials of two phenolic compounds are very close. Here, we have developed a simple electrochemical method for the selective determination of CT by using bare indium tin oxide electrodes and employing CT redox cycling by hydrazine. The cyclic voltammetry of CT and HQ was investigated in Tris buffer (pH 9.0), phosphate buffered saline buffer (pH 7.4), and acetate buffer (pH 4.5). Especially in Tris buffer, the anodic peak potential of CT is much lower than that of HQ, resulting in a large difference between two peak potentials (ca. 0.4 V). The difference allows the selective determination of CT in the presence of excess HQ. The anodic current of CT is amplified using CT redox cycling by hydrazine, which also helps to stabilize CT and HQ in Tris buffer for several hours. The detection limits of CT in Tris buffer containing 0.1 mM HQ are 1 μM and 10 μM in the presence and absence of hydrazine, respectively.