SPECROPHOTOMETRIC DETERMINATION OF CHLORINE DIOXIDE WITH CRESOL RED

Trace amounts of chlorine dioxide in water were determined by spectrophotometric procedures based on the reduction of Cresol Red (CR), a pH indicator. A linear relation was obtained between the absorbance and the amount of chlorine dioxide in the range of 0.004 to 1.36 ppm. The optimum pH for the reaction of chlorine dioxide with CR was 3.0 and the optimum pH for the absorbance measurement was 13.0. The reaction of CR with chlorine dioxide was very specific, and not influenced very much by such ions as iron(III), sodium, potassium, copper(II), magnesium, zinc, manganese, sulfurous and lead ions. The lower limit of determination of this method was 4 ppb.