Simultaneous Electroanalysis of Hypochlorite and H2O2: Use of I−/I2 as a Probing Potential Buffer

Sodium hypochlorite (NaClO) and hydrogen peroxide (H₂O₂) have been simultaneously analyzed, for the first time, using a simple and rapid potentiometric method. The present method shows a high sensitivity, selectivity and satisfactory reproducibility. Pt electrode was used as an indicator electrode and the I₂/I^? redox couple was used as a probing potential buffer. The large difference in the rates of the oxidation of I^? by the two oxidizing agents, that is, the oxidation of I^? by NaClO is by several orders of magnitude faster than that by H₂O₂, enabled the selective analysis of these two species. Based on such a large difference in the rates, a momentary potential response corresponding to the oxidation of I^? by NaClO and another quite slow one by H₂O₂ could be obtained. Factors affecting the selectivity as well as the sensitivity, such as the concentrations of molybdate (used as catalyst for the oxidation of I^? by H₂O₂), H⁺, I₂, and I^? in the potential buffer were examined. The expected Nernstian responses were obtained over a considerable range of the concentrations of the two oxidizing agents with slopes of 30.5 and 29.9 mV for NaClO and H₂O₂, respectively (in a close agreement with the theoretical value, that is, 29.6 mV) and with a detection limit in the submicromolar range (0.2 μM).