Development of a selective and sensitive measurement method for permanganate and its first quantification under...

Environmental water typically contains manganese, and when treated with ozone (O₃), MnO₄^- is produced, sometimes turning the water pink. However, there has been no measurement method that could specifically detect only MnO₄^- with sufficient sensitivity. Furthermore, the MnO₄^- concentration during ozonation has never been reported. Therefore, as an initial step in this study, we developed a selective and sensitive method for quantifying MnO₄^-, which is unaffected by other oxidizing agents (O₃, H₂O₂, HClO, HBrO, and Cr₂O₇^2-) and has a 4 nM limit of quantification-eight times lower than that of existing methods. This method is based on the mechanism in which MnO₄^- reacts with p-vinylbenzoic acid to produce 4-(1,2-dihydroxyethyl)benzoic acid even in the presence of dissolved iodide ions, whereas other oxidizing agents are reduced by the iodide ions. Using the newly developed method, the concentration of MnO₄^- produced during the ozonation of river water was measured while varying the reaction conditions. Under all conditions, MnO₄^- was rapidly formed within 30 s after ozone addition and tended to remain present. This study provides a powerful tool for investigating manganese oxidation in ozonation and is expected to facilitate the identification of optimal conditions for efficient manganese removal.