Determination of residual chlorine in city water by 4, 4'-bis-dimethylamino-thiobenzophenone.

Abstract

City water always contains 1 ppm or less chlorine for sterilization. The residual chlorine was determined by Michler's thioketone (4, 4'-bis-dimethylamino-thiobenzophenone) spectrophotometrically. City water (10 ml) was mixed with 1 ml of 0.2 M acetate buffer solution (pH 4) and 5 ml of Michler's thioketone solution which was prepared of 0.5 ml of concentrated hydrochloric acid, 4 mg of the ketone and 100 ml of 1-propanol in a 25 ml test tube with a ground stopper with shaking. After 10 min the absorbacne at 650 am was measured in a 10 mm glass cell. The calibration graph showed a straight line which passed through the origin and the molar absorption coefficient was 7.65 × 10⁴, dm³ mol^-1 cm^-1. Coexisting cations and anions in city water in this district did not disturb the determination. The method was applied to flow injection analysis. The reaction solution contained 40 mg of the reagent and 0.5 ml of concentrated hydrochloric acid in 1l of ethanol, and the carrier solution was made of 950 ml of 0.1 M formate buffer solution (pH 3.5), 50 ml of 0.01 M EDTA and 2 ml of 1/500 % (w/v) Triton X-405. Each flow rate was 1.7 and 1.3 ml/min, respectively. The peak height was proportional to the concentration of chlorine over the range of 01.5 ppm.