| abstract |
The present invention provides a composition for measuring residual chlorine concentration in the sample water, which is an aqueous solution comprising a specific benzidine compound, e.g., N,N'-bis(2-sulfoethyl)-3,3'-dimethylbenzidine disodium salt, and a surfactant, wherein the content of the surfactant is set to be 0.5% by weight or more and to be 0.5 weight-fold or more of the content of the benzidine compound, and the pH is adjusted to be in the acidic region. n This composition can prevent the benzidine compound from crystallizing in the aqueous solution under the low temperature condition such as in winter season or the like. |