2 Lines for Different Types of Samples and Applications
Under acidic conditions, chloride ions are also oxidized by potassium permanganate. To prevent these ions from reacting, a silver nitrate solution must be added to cause the chloride ions to be precipitated as silver chloride. For this reason, the acid method is suitable when the concentration of chloride ions in the sample solution is low (no more than 10 times the full scale of the measurement range).
When measuring sample water such as seawater that includes many chloride ions, it would be impossible to eliminate the interference effect of the chloride ions with the acid method. For these types of samples, the alkaline method is used. With the alkaline method, the chloride ions are not oxidized by potassium permanganate, so COD can be measured without the interference effect of the chloride ions.
*COD : Chemical Oxygen Demand
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