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Topic: Elimination the interference of Chloride in COD seawater analysis  (Read 16082 times)

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Offline carnation

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Hi everyone,
I'm doing experiments on seawater analysis. My concern is the interference of Chloride ion. When we determine COD (Chemical Oxygen Demand), we used Potassium Bichromate as oxidizing agent and Choride ion will react to Bichromate and it cause serious error. Ater looking up the Standard method for the examination of water and wastewater, I found that using HgSO4 will eliminate partly the interference of Chloride, but this method is just suitable to the maximum of Chloride about 2g/l. In seawater the average amount of Chloride ion is about 30 - 35g/l.
Could any of you recomend me any advice, document or website that I can find the suitable method.

Offline Borek

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Re: Elimination the interference of Chloride in COD seawater analysis
« Reply #1 on: December 13, 2006, 12:29:58 PM »
I am more then sure that there exists specific methods of COD analysis for sea water, that don't require you to treat Cl as intereference, as it is systematically taken out of the solution (or oxidizing agent is not strong enough to oxidize Cl- to Cl2).

What I am aiming at is - don't try to get rid of chlorides, try to find other COD deterimnation method.
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Offline kevins

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Re: Elimination the interference of Chloride in COD seawater analysis
« Reply #2 on: December 14, 2006, 12:18:41 AM »
We have an experience for COD determination upto 40g/L of Chloride, we add sufficient amount of HgSO4 into the solution. The detection limit is very high and up to 40mg COD/L (1mg COD/L in clean water). :'(

Offline chiralic

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Re: Elimination the interference of Chloride in COD seawater analysis
« Reply #3 on: December 14, 2006, 02:17:57 AM »
Hello Carnation:

I recommend you a couple solutions:

Dichromate Reflux A Proposed Method for Chemical Oxygen Demand Chloride Correction in Highly Saline Wastes by Frank J. Baumann in Analytical Chemistry Vol. 46, NO. 9 (1974) 1337
(The complexing method, as currently practiced, using a weight ratio of HgS04:Cl equal to 1O:l
will yield reproducible results at chloride concentrations up to 5,000 mg/l.)

and Paper from Malaysian Journal of Chemistry (2003) 5:067-072, intitled: Minimizing the use of Mercuric Salts for Chloride and Bromide Corrections in Chemical Oxygenb Demand Test by Choon Fah et.al. (Chloride <10000mg/L; also in this paper "neutralize" interferences by Chloride
using HgSO4 up to 3 g/L...)

In the last paper, the authors suggest change of HgSO4 by Cr(NO3)2 and Al2(SO4)3

I can send you a copy of these papers to your a private email....please send me a email to chiralic@gmail.com...

Regards,

Chiralic

Offline carnation

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Re: Elimination the interference of Chloride in COD seawater analysis
« Reply #4 on: December 14, 2006, 12:12:17 PM »
We have an experience for COD determination upto 40g/L of Chloride, we add sufficient amount of HgSO4 into the solution. The detection limit is very high and up to 40mg COD/L (1mg COD/L in clean water). :'(
Thanks for your information. I am not used to with analysing COD in sea water. Because you have experience in this field, it's very kind of you to let me know your method. Do you have any trouble in precipitation of AgCl cause by AgSO4 as a catalyst and Cl in the sample ?
Best regard

Offline natrium

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Re: Elimination the interference of Chloride in COD seawater analysis
« Reply #5 on: December 15, 2006, 11:43:17 AM »

You should take a look to: Standard Methods for the Examination of water and waste water, from the

american public health association.... There is all you can find about water analysis... I hope this can help

you....


Offline kevins

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Re: Elimination the interference of Chloride in COD seawater analysis
« Reply #6 on: December 17, 2006, 11:04:26 AM »
If you add Hg before Ag, that is no difficult for the Ag catalyst. Please try. ;)

Offline carnation

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Re: Elimination the interference of Chloride in COD seawater analysis
« Reply #7 on: December 18, 2006, 06:11:42 AM »
If you add Hg before Ag, that is no difficult for the Ag catalyst. Please try. ;)
Thanks, I will try

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