How do I interpret the chloride interference table found in method 8000?
Interpreting the chloride interference table in method 8000
This COD test is most accurate in the middle of the concentration range where there is a higher ratio of reagent to chemical oxygen demand (COD), insuring that there is enough oxidizing potential for accurate COD measurements. If the COD or chloride is at a high enough concentration that the sample needs dilution, it would be recommended to make the dilution high enough to eliminate the chloride interference. Column 1 is the maximum chloride concentration based on the amount of mercuric sulfate that has been added to the reagent. Column 2 is the chloride concentration that is recommended for a diluted sample. Column 3 is the maximum chloride concentration if an additional 0.50 g of mercuric sulfate was added to the reagent vial. At the high end of the concentration range of that reagent, dilute the sample and minimize the chloride concentration to 1000 ppm or less.