PRINCIPLE

The COD determination as described in “Standard Method” has been modified for automatic monitoring. The sample is pre-added with mercuric sulfate to prevent chloride interference. Then add mixture of concentrated sulfuric acid and phosphoric acid . The system by esothermic reaction arrived at 110°C. After white measure, potassium dichromate in acid is added. The depletion of the hexavalent chromium ( yellow to green) due to the oxidation-reduction reaction with the sample is measured colorimetrically. The green color is measured at 640 nm

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