i have a sample that i want to find its COD. i had fined a COD testing method ( that uses permanganate for measuring COD) but i dont know Accuracy of this method. now i want make some standard solutions with specific CODs and test them and finally find Accuracy of my method.
My recommendation is to purchase standard solutions with known COD levels to calibrate your results. That way you do not introduce any more uncertainty to your analysis. Attached is a link to the one we use. Hope that helps.
http://www.hach.com/cod-standard-solution-1000-mg-l-as-cod-nist-200-ml/product?id=7640193222
HI dear Safie Anjomshoa
As Steven Barber said you can purchase standard solutions of KHP but you can make it easily. Now I have a project about chemical oxidation demand in Research Institute of Petroleum Industry (RIPI). If you think I could help you just lemme know. Remember that all of reagents are highly toxic.
Hi Safie, I have another idea. You can make an announcement here on Research Gate that you are looking for standard solutions that other researchers might not be using anymore since their project ended, etc. That way they wouldn't go to waste and unnecessarily disposed of. Offering to pay for the shipping would help.
Good luck,
-Steve
Dear Saife,
You can dissolve 0.4686 g of glucose in distilled water and diluted to 1000 mL. It will yield a 500 mg /L COD solution. You can make the sample according to your requirement.
Reference: Standard method for the examination of water and wastewater (APHA, AWWA, WPCF).
Best!
As per the first answer, the correct standard to use is phthalate monobasic (also known as potassium hydrogen phthalate - KHP). Use ACS grade or better. eg Sigma product 179922. It is not expensive (especially when compared to the COD reagents themselves) and the solid can be kept in a dry dark cupboard for many years.
The standard is not toxic, and has the advantage of being commonly used for TOC standards too.
Use 425mg of KHP into 500ml of DI water in a volumetric flask. This = 1000mg/L.
This is good for a couple of months if kept in the fridge. Throw out after that - make more. To maximise standard life dry volumetric flask and KHP in 105 Deg oven and use autoclaved water. You can also aliquot into 50ml centrifuge tubes and freeze if you want to keep it longer.
Do not buy or use leftover liquid standards - once they are opened they should be disposed of in the 2-3 months, and you never know who has put what dirty tips into them or poured back solution from non-sterile beakers. Your time and the COD reagents are worth far more than the 25 cents ($AUD) of KHP it cost to make the new standard.
Glucose standards have a much shorter shelf life due to microbes, I would recommend against them.
Theoretical oxygen demand for KHP is about 1.175 mg Oxygen per mg KHP in this way if we need to prepare a KHP standard solution having 500 mg/L of COD we have to take 500/1.175=425.53 mg of KHP dissolve in distill water and make up the volume 1000
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