Determination of microgram and nanogram amounts of active chlorine in water by iodine—azide reaction induced by thiosulphate or thioammeline

Abstract

An indirect determination of active chlorine in water based on the induced iodine—azide reaction and measuring the amount of thiosulphate or thioammeline oxidized by chlorine is described. The oxidation products do not induce the iodine—azide reaction. The decrease in the amount of thiosulphate or thioammeline taken in excess with respect to chlorine is proportional to the amount of chlorine in the sample. Three procedures for the determination of chlorine based on this principle were applied: back-titration of an excess of iodine in the reaction medium, titration with an iodine solution which is very slowly added to the sample solution at a constant rate and continuous-flow determination. The concentration ranges for the determination of chlorine are by back-titration 1–12 μg or 0.1–0.7 μg in a 5-ml sample in the presence of thiosulphate or thioammeline, respectively, by titration with iodine solution 3–20 ng in a 10-ml sample in the presence of thioammeline and by continuous-flow determination from 0.5–5 μg l −1 to 0.05–1.5 mg l −1 depending on the reaction conditions and the inductor applied.