The analysis of chlorine dioxide and its oxychlorine by products in water is a difficult topic due to the volatility of chlorine dioxide and to the interferences from other species with standard test methods. In the real samples, this is further complicated as chlorine dioxide is often used in a system which is dynamic and therefore sampling is also important.
The USEPA require that both chlorine dioxide (ClO2) and chlorite (ClO2–) are monitored daily at the start of a distribution network and that chlorite is measured less frequently at various points throughout a network. Chlorate is not required, although is included under the Information Collection Rule.
The following are methods that have been approved by the USEPA for ClO2 monitoring:
As DPD has been removed as a standard method for determining ClO2 by the AWWA Standard Methods committee, the EPA will also probably remove it sooner rather than later. As for chlorite, there are a few methods (such as ion chromatography) approved for chlorite monitoring. None of them are truly portable as the ChlordioX Plus is making it the only portable USEPA approved method for determining chlorite.
Other colorimetric methods are available however none are approved for compliance testing.
This summary of methods is based on White’s Handbook of Chlorination and Alternative Disinfectants by the Black and Veatch Corporation, published by Wiley in 2010.
See here for a list of EPA methods approved for chlorine dioxide and chlorite monitoring under the alternative test methods program.
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US-EPA approved technology for measuring free chlorine, chlorine dioxide and chlorite on one compact, field instrument.
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