Dear,

From the results of uniform quality control of COD analysis in Japan, held last year, we had to admit the gap or diffrence of analysisi result between using silver sulfate and silver nitrate.

Maybe changing catalyst for COD analysis will cause a difference in analysis value of COD.

I think it is better not to change the catalyst for COD analysis.

Thank you.

The COD values will different with AgNO3

Additional reactions with NO3 anion will take place in the solution affecting the COD.

Presence of Chlorides boost COD value. For this purpose Mercuric sulfate is used to avoid Chlorides interference. Some researches have suggested pre-treatment with silver nitrate in a controlled manner.

Presence of NO2 ions also add to COD values. But NO3 ion has got no such interference.

If SO4 ion is working as catalyst, we have to Search out sulfate salt.

If Ag ion is working as catalyst, we can search out alternative of silver.

If both ions (Ag and SO4) are working as catalyst, we may have no alternative, or we may have other metallic salt as alternative, or a combination of two different salts in different composition.

Anyhow, I am also searching the answer. When I can access any such research, I will share here.

I am sure, some one may have studied this.

After continues search I came across few references about the alternate catalyst for COD. These are herein attached for discussion.

Regards

For removal of interference and use of Silver Nitrate see this attachment.

Does anybody have a mechanism for the interaction of nitrate with the COD analysis?

I think nitrite (NO2) interfere with COD results, Nitrate (NO3) has no such interference.

I will check it again.

Better no to change the reagents to avoid interference in real waste water sample.

Here are some literatures that may be helpful for those interested in COD.