Analysis techniques of low COD in water sample with high chlorine ion

The interference mechanisms of chlorine ion and the method and principle of measurement of COD using the potassium dichromate oxidation method were analyzed. Based on the digestion time experiment on chlorine ion, a method was proposed to measure COD. First, potassium dichromate and oil of vitriol were heated for 0.5h without silver sulphate added. Then, 0.3g silver sulphate was added into the mixture after a 0.5h-cooling. The total apparent COD was measured when the heating and recycling process was continued for 1.5h. The low COD in water samples with high chlorine was rectified by the apparent COD curve of chlorine ion. This method, with the advantages of high duplicate, no pollution, low cost, can well reflect the COD in waters and is a cleaning analysis method worthy of use in practice.