Photometric determination of chlorine dioxide, chlorite ion and residual chlorine in swimming pool waters with the reagent N,N'-bis(2,4-di-sulfobenzyl)tolidine (SBT)

A method for the determination of chlorine dioxide, chlorite ion and residual chlorine in swimming pool waters with the reagent N,N'-bis(2,4-di-sulfobenzyl)tolidine (SBT) was examined. It was assumed that the phosphate buffer solution of pH 6.3 was used to receive the obstruction of free residual chlorine when chlorine dioxide was measured using the acetate buffer solution of pH 5.0-5.6. However, the absorbance decreases rapidly when phosphoric acid solution is used. Therefore, after the reagent had added, the absorbance spectra was measured at once. If the sulfuric acid solution is added after the potassium iodine solution is added, the free residual chlorine doesn't influence the determination of chlorine dioxide. Measurements by SBT photometric method that had been developed this time since the swimming pool waters was measured were corresponding to measurements by N,N-diethyl-p-phenylenediamine (DPD) photometric method well.