Determination of Ozone In Water By The Indigo Method: A Submitted Standard Method

The indigo method for the determination of ozone as formulated for the new Swiss Standard Methods for Drinking Water Analysis is presented with an international list of suppliers of indigo trisulfonate. Such a new selective and simple method will be needed in many countries because current methods for ozone analysis are generally non-selective when applied on real drinking waters or wastewaters. Ozone rapidly and stoichiometrically decolorizes indigo trisulfonate in acidic solution. The decrease in absorbance at 600 nm is linear with ozone residual and is 0.42±0.01 cm-1 per mg/L (Δ = 20,000 L Mol-1cm-1 at 600 nm when compared to the uv absorption of pure ozone of = 2900 L Mol-1cm-1 at 258 nm). The limits of detection are 2 µg/L for an instrumental and 10 µg/L for a visual field method.