Spectrophotometric Determination of Ozone in Water by the Color-Fading Reaction of Sodium Indigo Disulfonate

In a H3PO4-Na2HPO4 buffer medium of pH 2.0, fading of color due to the reaction of sodium indigo disulfonate with ozone was observed. It was found that the magnitude of decrease in absorbance measured at 610 nm kept a linear relationship with the concentration of ozone in the range of 0.12-3.0 mg·L-1. Apparent molar absorptivity of the reaction system was found to be 1.8×104L·mol-1·cm-1. Based on these facts, a spectrophotometric method for determination of ozone in water was proposed. Water samples were analyzed by the present method, giving values of RSD′s (n=20) in the range of 0.6% to 2.8%.