Comparative studies for the demonstration of chlorine in drinking and washing water using o-tolidine and diethyl-p-phenylenediamine (DPD).

The detection of free chlorine with the aid of o-tolidine is connected with systematic errors within the range of concentration below 0.1 mg/l and above 0.7 mg/l, reproducibility being otherwise good. In the case of the simultaneous presence of free and bound active chlorine, especially in bathing water, this method determines 50...70% of varying shares of the bound chlorine in dependence on the reaction time. Determination of chlorine with the aid of diethyl-p-phenylenediamine (DPD) as to the prescription according to Palins is free of systematic errors and makes a correct determination of free and bound active chlorine possible with detection limits of 0.03 mg/l. The DPD method is recommended as a standard method, and for the water-works practice a battery-operated chlorine photometer is developed for rapid determinations.