Temperature impact on monochloramine, free ammonia, and free chlorine indophenol methods

摘要

A commercial colorimetric indophenol (IP) method is used for determining monochloramine (NH_2Cl) concentrationsfor process control in chloraminated public water systems and chloramine-related research. TheNH_2Cl – IP method excludes some quality control procedures typically included in drinking water methods andis not approved by the United States Environmental Protection Agency (U.S. EPA) for compliance monitoring.Therefore, the authors developed and validated a more complete NH_2Cl–IP method, building on the commercialtechnique, as a candidate for future approval. During method development, temperature impact on color developmentwas investigated. Color development time increased as temperature decreased. Below 20 °C, timesneeded for full color development were greater than those reported in the commercial method, reachingnearly three times longer at 5 °C. This observed temperature dependence also applies to free ammonia andfree chlorine indophenol methods. To avoid measurement errors of samples analyzed below 20 °C, use of reactiontimes determined in this study is recommended for these indophenol methods.