As I have prepared a synthetic sample of acetic acid anhydrous which is supposed to give me COD value of 200 mg/L but it is giving me only 50 mg/L all the reagents are checked thrice and made again two times following standards methods of examination water and wastewater.
Hi.
You give little information for a proper reply. Which method are you using (open or closed reflux)? If closed, titrimetric or colorimetric method?
Anyway, I would recommend you to "calibrate" your method with potassium hydrogen phthalate (KHP) as standard. It has a COD of 1.176 mg O2/mg.
Acetic acid is volatile and one may expect a little lower COD than the theoretical value. But from 200 mg/L down to 50 mg/L is too much of a drop. I think you need to give more details i.e. step-wise preparation procedure and calculations.
If you use a long reflex condenser, it may work. Besides this, add chemicals reagents slowly. As mentioned by Mohamed Hussain Isa, acetic acid is sensitive to heat, therefore, reagents, especially sulfuric acid should be added very slowly. For comparison, as reference, run sugar solution. I hope, the problem will be solved.
First of all you will check oxalate standard which may be it was spoil or contain moisture.
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