Can someone please explain what the intrinsic differences are between the Indian Standard COD method and the APHA method (particularly using 0.1 N FAS vs. using 0.25 N FAS). What are the advantages or disadvantages of using one method over the other?
Also, how does one incorporate the dilution factor into the COD calculation?
Thanks!
It is really irrelevant. If the sample has high COD you need to use a diluted FAS solutio such that you don't end up consuming 0.1 mL, which will incorporate a lot of error in your quantification. If COD in sample is low use 0.25 N.
At the end of of your COD calculation just multiply by the dilution factor.
I am with the opinion of the Professor Omar Gonzalez-Ortega.
The increase in dilution means an increase in the error margin
Using the appropriate dilution avoiding random errors
Hi Michela -
See attached link for US EPA method - it shows the calculation. Upon experimentation with your environmental sample you will characterize which FAS solution you will use, it will depend on concentration of COD in your sample(s). If you start with 0.1 and are using too much titrant for end point then you would switch to the higher concentration FAS, you just don't want to use so much (in terms of volume) that it is going to dramatically change the final volume.
https://www.epa.gov/sites/production/files/2015-08/documents/method_410-3_1978.pdf
