AWWA JAW60489

Chlorine dioxide (ClO₂) is used at many water treatment plants for disinfecting potable water. In such applications, having a simple, convenient, and reliable analytical method to measure the concentration of ClO₂ can simplify the use of it as a disinfectant. However, the presence of the Cl₂O₄^- complex, which forms in ClO₂ solutions in the presence of chlorite ion, can result in significant error in the spectrophotometric measurement of ClO₂. In this article, the authors demonstrate the significance of the Cl₂O₄^- complex and report the formation constant (K_eq) and the molar absorptivity of this complex. Based on the K_eq and the molar absorptivity values, the authors propose two methods to correct for the presence of the complex and suggest the use of one equation in particular. By using the equation suggested, the authors demonstrate that the error of the determined ClO₂ concentrations is reduced to the level of errors associated with the spectrophotometric measurements. Includes 16 references, tables, figures.