Colorimetric detection of hypochlorite in tap water based on the oxidation of 3,3′,5,5′-tetramethylbenzidine

We have developed a simple method for the colorimetric detection of hypochlorite in tap water based on the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). In aqueous solution at pH 4.0, hypochlorite, an oxidant, rapidly converts colourless TMB to a blue oxidized form. The presence of hypochlorite in tap water can in this way easily be detected with the naked eye, based on the obvious colour change. The system can detect concentrations of hypochlorite as low as 0.05 mu M with an excellent linear relationship and good selectivity.