AWWA WQTC65959

This paper describes two improvements of the amperometric titration method (Standard Method 4500-ClO₂ E) for chlorite residual analysis and discusses the interference of nitrite with this method. First, the addition of starch solution into water samples provides a color indicator of the titration end point, aiding the ease of analysis. Second, DPD total chlorine measurements can be used to check the titration accuracy in the method's chlorine titration step. Nitrite was found to cause significant interferences with the amperometric titration method, yet this interference has been largely ignored in practice. This study investigated the magnitude of the nitrite interference; possible mechanisms are discussed herein. If nitrite levels exceed 0.04 mg/L as nitrogen, other chlorite analysis methods such as ion chromatography and colorimetric methods are preferred due to the possible nitrite interference with the amperometric method. A Hach colorimetric method using Horseradish Peroxidase/Lissamine Green B reagent (similar to U.S. Environmental Protection Agency Method 327.0) was beta-tested in parallel with the amperometric titration method. Although the Hach colorimetric method will not likely come to market as indicated by Hach Company, the method was useful in identifying the analytical interferences of the amperometric method. Includes 9 references, table, figures.