A Method for Simultaneous Quantification of Chlorine Dioxide and Hypochlorous Acid/hypochlorite and its Application to Disinfection Products

A novel high performance chromatographic method was devised to simultaneously quantify chlorine dioxide and hypochlorous acid/hypochlorite, leveraging their similar chemical properties but distinct toxicities. In this study, it consists of a two-step derivatization reaction: The first step is the reaction of hypochlorous acid/hypochlorite with 2,6-dimethylphenol in a water matrix to produce 4-chloro-2,6-dimethylphenol; the second step is a reaction in which iodine ions added after the first step react with chlorine dioxide to produce iodine and then react with 2,6-dimethylphenol to produce 4-iodo-2,6-dimethylphenol. It was confirmed that the concentration of 4-chloro-2,6-dimethylphenol produced was proportional to the total concentration of hypochlorous acid/hypochlorite, and the concentration of 4-iodo-2,6-dimethylphenol was proportional to the concentration of chlorine dioxide. With a detection limit of 0.011 mg/L for chlorine dioxide and 0.009 mg/L for hypochlorous acid/hypochlorite, the calibration curve showed excellent linearity (r2=0.999) in disinfectant solution. This sensitive and selective method is well-suited for the routine analysis of chlorine dioxide and hypochlorous acid/hypochlorite in water and disinfection byproducts.