Spectrophotometric determination of chlorine dioxide

Spectrophotometric procedures based on the oxidation of chlorophenol red (CPR), a pH indicator, can determine trace amounts of chlorine dioxide in water. Procedures for measuring three concentration ranges have been developed: 0–0.1 mg/L, 0–0.2 mg/L, and 0–1.0 mg/L. A total of four reagents and a laboratory or portable spectrophotometer were used. The reaction of CPR with chlorine dioxide is very specific, with no interference noted from hypochlorite, chlorite, chlorate, chromate, permanganate, ferric iron, chloramines, turbidity, or sample temperature. At a 0.46‐mg/L chlorine dioxide concentration, the precision of the method as standard deviation is ±0.003 mg/L.