EFFECT OF DIMETHYLSULFOXIDE AS A MASKING AGENT FOR AQUEOUS CHLORINE IN THE DETERMINATION OF OXYCHLORINES

The aim of this work was to demonstrate that dinethylsulfoxide (DMSO) is an excellent masking agent for aqueous chlorine in the determinatio n of other oxychlorines. By the addition of excess DMSO,specific absor bance of free chlorine disappeared, and the oxidation of iodide to iod ine by chlorine was completely prevented. Chlorine dioxide, chlorite a nd chlorate were not affected by the co-existence of excess DMSO, but chlorosulfamic acid, showed results comparable to free chlorine. By us ing ion chromatographic analysis of the mixed solution of free chlorin e and DMSO, chloride was recovered as the only anionic species and its molar concentration was approximately twice the initial chlorine conc entration. DMSO seems to reduce and mask chlorine completely, without affecting other oxychlorines. Chlorine and DMSO reacted in the molar r atio of 1:1. The reaction seemed to be second-order. The rate constant was larger at a lower pH, and it was dependent not on a concentration of total chlorine, but on that of hypochlorous acid. The redox potent ial of DMSO was higher at a lower pH, and only hypochlorous acid would have a redox potential high enough to oxidize DMSO in acidic conditio ns. These results suggest that DMSO reacts with hypochlorous acid stoi chiometrically. In practical use, DMSO may be successfully used as a m asking agent for aqueous chlorine.