COD Testing FAQs

Where do the errors of COD detection mainly come from?

Chlorine is the most influential factor in COD detection. Each COD test vial used in the potassium dichromate method contains mercury sulfate, a substance capable of removing chlorine interference at concentrations listed in the Hach Method Manual. The vacuum pretreatment device used in the Mil method can remove chlorine with a concentration of 1000 mg/.

How to remove the effect of chlorine on COD detection?

Prepare a blank containing deionized water and the same chlorine concentration as your sample. The blank will quickly turn very dark after adding the digest, but then you can subtract the effect of chlorine and get a test result that can be applied to your sample.

Can I use the same COD blank for multiple assays?

Answer: The same blank sample can be reused for multiple experiments using the same experimental bottle. This blank must be kept in the dark. Measure the absorbance of the blank over time to check that the results are stable. Use bottled deionized water to zero the instrument in absorbance mode, and then measure the absorbance of the blank sample. Record the test results. When the absorbance changes more than 0.01 absorbance units, it is necessary to prepare a new blank sample.

How to verify the accuracy of COD test results?

Use a COD standard solution that falls within the concentration range you are using. Use this standard solution as your sample for testing. If your test results are close to the standard concentration, you can be confident that your instruments and reagents are working properly and that your test is operating correctly.