Abstract The active chlorine in 84 disinfectant was determined by back titration. The active chlorine in 84 disinfectant and K2Cr2O7 can be quantitatively reacted with Fe2+ in the sulfuric acid. The excess Fe2+ in the active chlorine react with 0.001 0 mol/L K2Cr2O7 standard solution, and active chlorine content was calculated. Active chlorine within 0~5.50 mg was linearly dependent on the K2Cr2O7 standard solution, the correlation coefficient is 0.999 8 and the detection limit of the method (3S/k) is 6.8 μg. This methods for the determination of active chlorine in samples was simple, fast, and less interference than traditional titration. The relative titer is TNaClO/K2Cr2O 7=0.248 3 mg/mL.
