Comparison of Hydrogen Peroxide to Ammonium Ions and Sulfite as a Free Chlorine Quenching Agent for Disinfection By-Product Measurement

Abstract

Hydrogen peroxide is a potential dechlorinating agent that can preserve chlorinated drinking water samples for the determination of disinfection by-products (DBPs). The impact of hydrogen peroxide on the storage of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and adsorbable organic halides (AOX) generated by chlorination in a model of natural water was investigated and compared with parallel samples quenched by sodium sulfite and ammonium sulfate. Positive errors of up to 9 μg/L for THMs, 19 μg/L for HAAs, 1 μg/L for HANs, and 22 μg Cl/L for AOX were found after adding ammonium and storing for 9 days at 4°C, primarily due to the continued formation of chloroform, bromodichloromethane, dichloro- and trichloro-acetic acids, and dichloroacetonitrile. Hydrogen peroxide and sulfite led to smaller errors in the determination of THMs, HAAs, and AOX, while HANs degraded in the presence of sulfite. Hydrogen peroxide was the most suitable dechlorinating agent of these three for preserving THM, HAA, HAN, and AOX samples, provided that the relatively slow chlorine quenching reaction time (e.g., 3–4 min) is acceptable.