Spectrophotometric Determination of Trace Amounts of Chlorine Dioxide with the Fading Reaction of Chlorophenol Red

A sensitive spectrophotometric method for the determination of trace amounts of chlorine dioxide based on the fading reaction of chlorophenol red by chlorine dioxide has been developed in the alkaline solution. The maxmium fading wavelength is at 575 nm, The ΔA(A 0-A) is proportional to the concentration of chlorine dioxide, its molar absorptivitie is 2 6×10 4 L·mol -1 ·cm -1 and the detection limit is 2.0 μg/L for chlorine dioxide. The method has high selectivity and has been applied to the determination of chlorine dioxide in tap water samples with satisfactory results.