Assessment of some aqueous residual chlorine measurements

Conclusions Sodium hypochlorite solutions, filter effluent, plant effluent, and tap water were analyzed by the amperometric titration (AT), residual chlorine electrode, (EL), and DPD ferrous titrimetric (DPD) methods and the results were compared for the range 0.2 to 2.0 ppm residual chlorine. Overall precision for measurements by all three methods and in three laboratories was 10% RSD for TARC and 20% for FARC. Amperometric titration was judged the method of choice because of precision of measurements, simplicity of operation, and capability for both TARC and FARC determinations.A rapid initial decay of TARC in stored water samples containing high initial levels of FARC was observed. Residual chlorine values obtained from such samples after storage could not be meaningfully correlated with other water parameters obtained during the monitoring study. Correlation was only meaningful for water samples which did not show a significant change in residual chlorine levels after storage.