Do you know aproximativaly which is the chloride concentration ?. One option is to dilute the sample, provided that the resulting COD concentration is above the limit of quantification of the method.

By dilution it is possible to measure the COD of sample by conventional method. There may be possibility of some approximation in the results obtained.

I tried dilution of sample, but the organic content in the solution also get diluted very much. So, the bland and sample titre values are almost same. that means it shows no COD. Also, I used mercury sulphate to suppress the chloride ion concentration, even though i am not able to get the proper COD value. The error percentage which i am getting more than 60 %.

The origin of chloride is chlorine (Cl2). Chlorine is a great oxidizer of organics to

include micro organisms. This is why chlorine is a powerful disinfectant in water

treatment. Cl2 works well because the two Cl atoms share an electron, and readily

receive two electrons to become two stable chloride ions (Cl

-2

). This electron

grabbing oxidizes (or destroys) micro organisms, but adds many interferents to

the COD sample.

The reaction between chloride and silver sulfate creates silver chloride (AgCl).

The reduction of silver sulfate correspondingly reduces the activity needed to

oxidize straight chain hydrocarbons, a negative interferent one would think. But

the cloudiness of silver chloride precipitate causes a false positive absorbance

value. Furthermore, the rigorous COD digestion can actually result in the reaction

of dichromate with chloride to form chromic acid (and the elemental form of

chlorine). Adding chlorine to the sample causes a positive interference.

Suffice it to say that all chloride interferences are overcome by complexing

chloride with mercuric sulfate (HgSO4). Chloride concentrations >2,000 mg/L

cannot be corrected. High chloride samples must be run titrimetrically by EPA

410.3, COD for Saline Waters.

EPA approved COD methods for NPDES reporting:

determinative sample

Method Year MDL mg/L technique____ size ml

EPA 410.1 1971 >50 Titrimetric 50

EPA 410.2 1971 5 – 50 Titrimetric 50

EPA 410.3 1971 >250 Titrimetric 50

EPA 410.4 1978 3 – 900 Colorimetric (automated) 2.5

EPA 410.4 1978 20 – 900 Colorimetric (manual) 2.5

Hach 8000 1980 3 – 150 Colorimetric 2.0

Hach 8000 1980 20 – 1,500 Colorimetric 2.0

SM 5520 C 1998 400 Titrimetric 2.5 – 10

SM 5520 D 1998 900 Colorimetric 2.5 – 10

All colorimetric COD methods creat

I would consider using sodium thiosulfate to neutalise the chloride. Either that or dilution.

@Michael_K: Thiosulfate works for chlorine and not chloride. This method is frequently used in tap water sampling to stop chlorine-related reactions.

@Boopathy: If not properly addressed, chloride is indeed a severe problem in COD analysis. According to the German norm (DIN 38409 H41-2) you perform a special pretreatment to samples with >1 g/L chlorine: You get rid of a significant amount of chloride by adding sulfuric acid to the sample and strip the chloride as HCl. Usually you close the reaction container with a special absorber (e.g. http://www.behr-labor.com/htemel/prods/01202f.html ) filled with CaOH2 and allow the mixture reacting for several hours. The remaining chloride is masked by the Hg.

Instead of measuring COD, you could measure TOC (total organic content). Chloride should not be an interference for TOC. There are literature rarios between COD and TOC. Alternatively you could measure both.

I agree with Thomas O'Connor. Measurement of COD requires the use of many chemicals, some of which are hazardous. TOC is the modern alternative.

Dear Boopathy Ramasamy,

You might have followed the APHA Standard Methods. Still I would like to request YOU to look for some Chloride correction options.

Otherwise, it remains as a challange with such a high Chloride concentration.

YOU may also try more rigorous digestion and go for analysis with NOVA - 60 (MERCK).

I would like to look forward to the eventual solutions, you have found out.

Thanks.

Regards.

Please see the attached list of related articles !

No possibility to add the file: I copied it for you:

1. Correlations among chlorine ion, COD and TOC in wastewaters from different sources

By Zhang, Xiuxia; Qin, Lijiao; Li, Yuguo; Xu, Nana; Li, Xiuling; Zhao, Chaocheng

From Huanjing Gongcheng Xuebao (2011), 5(4), 851-855. Language: Chinese, Database: CAPLUS

2. A new approach for chemical oxygen demand (COD) measurement at high salinity and low organic matter samples

By Kayaalp, Necati; Ersahin, Mustafa Evren; Ozgun, Hale; Koyuncu, Ismail; Kinaci, Cumali

From Environmental Science and Pollution Research (2010), 17(9), 1547-1552. Language: English, Database: CAPLUS, DOI:10.1007/s11356-010-0341-z

3. Chloride interference in the determination of COD of landfill leachate

By Yang, Shiying; Zhang, Wenyi; Shan, Liang; Yang, Xin; Wang, Ping

From Huanjing Kexue (2010), 31(4), 1014-1020. Language: Chinese, Database: CAPLUS

4. Method and device for removing high-concentration chloride ions during on-line detection of chemical oxygen demand (COD) of wastewater

By Ding, Guoqin; Zhong, Ming; Lin, Yongzeng; Luo, Jun; Wang, Jianquan

From Faming Zhuanli Shenqing Gongkai Shuomingshu (2010), CN 101634616 A 20100127, Language: Chinese, Database: CAPLUS

5. Complex biological degradability test of pharmaceutical waste

By Princz, Peter; Olah, Jozsef; Smith, Scot; Horvath, Imre

From Technical Papers of ISA (2001), 417(IMEKO Special Millennium Sessions, 2001), 27-36. Language: English, Database: CAPLUS

6. A new approach for chemical oxygen demand (COD) measurement at high salinity and low organic matter samples

By Kayaalp Necati; Ersahin Mustafa Evren; Ozgun Hale; Koyuncu Ismail; Kinaci Cumali

From Environmental science and pollution research international (2010), 17(9), 1547-52, Language: English, Database: MEDLINE

7. Chloride interference in the determination of COD of landfill leachate

By Yang Shi-ying; Zhang Wen-yi; Shan Liang; Yang Xin; Wang Ping

From Huan jing ke xue= Huanjing kexue / [bian ji, Zhongguo ke xue yuan huan jing ke xue wei yuan hui "Huan jing ke xue" bian ji wei yuan hui.] (2010), 31(4), 1014-20, Language: Chinese, Database: MEDLINE

Well, I see significant problems regarding the TOC determination. By using the persulfate method you will have too low readings because of the chloride and by using the combustion method the lab workers will "love" you because of the increased wear of the combustion tube and inactivation of the catalyst. If you chose TOC (and combustion) instead of COD consult the lab if they use a kind of matrix separation.

Dear Boopathy,

please find the correct requirement, why do you want to find COD in sea water? is sea water contaminated with some organic pollutants? how and what is source of pollutant? (bio masses or other organic solvents), can't you get any facts and figures COD in sea water? (from books, internet......).

sorry, I don't know the real requirement, as you mentioned above "For the sea water treatment", my idea is you don't need worry about the COD value,

first! treat the sea water to remove major ions (Cl-, Na, Mg, SO42-........)

then, find the COD in treated sea water in the normal way.

please don't add more and more HgCl2 to remove Cl-, just consider the environment.

still if you want to find the COD in sea water, just find TOC (as Thomas O'Connor and Patrick Brezonik said). sample dilution is not the good answer for this.

thanks,

AmilA.

Dilute the wastewater 100 times and estimate the COD by standard method mentioned in APHA book

I think, the intension is to store the water samples for needbased analysis of particular type of water quality in future depending on the nature of pollution.

But the main issue is how to preserve the water samples for such a long time year after year. What type of preservative is to be used without knowing the water quality to be analysed in future?

So it will perhaps be better, if the testing and analysis of all parameters is carried out and the Test Reports are saved for future use.

Hi, I am sorry that I made a mistake. Actually, the above update was supposed to be for the discussion initiated by Valenti Turu Michels in Water Quality section. But due to some technical problems, it has been uploaded here. So I would like to withdraw the same from here.

Thanks.

With Regards.

Hi, we are working with Hach Lange cuvette tests, like this one: http://www.hach-lange.de/view/content/facetsearch?fn=defaultParameters&fv=45443&type=Product

This test is fast and valid for chloride up to 4 g/L, but you can dilute it, as in your case.

firstly practicised the activated Cu,Pt,Sb compound and after then remove sludge by membrane method.

I dont know

There are preperative columns for chloride removal based on silver ions which are used for ion chromatography. Such a column may be used before COD is analysed e.g. by the hach-lange kit.

Vijay Charde ACS College, Koradi, RTM Nagpur University, Nagpur, India

The method for chloride correction in high saline waters is given in "Baumann, F.I. 1974, Anal. Chem. 46:1336".

I think if you use higher concentration of dichromate for COD estimation and repeat process with control sample with same salinity in distilled water and then making correction may solve your problem.

Please let me know how many methods for determination of chemical oxygen demand in natural water are there?

Please refer the method for chloride correction in high saline waters is given in "Baumann, F.I. 1974, Anal. Chem. 46:1336". It is also referred in APHA in the reference. I have done the experiment with high saline water and it gives +_5% accuracy.

Open reflux method for COD, you will find it in APHA standerd method.

Did you get your required answer? I am also searching for the same. And dilution is not the proper method....as there are manual and analytical errors. Apart from that, please let me know in case you do get a proper protocol for this one.

Yup i think i got one answer..check to see the relevance.. Document attached here...

Here is the procedure which i got to do the COD at saline condition. The procedure is almost similar to the procedure suggested by Ashwini Zaware.

Thank You Dr. Vyrides. I am using your method of COD analysis only.

thanks everyone for the suggestions.  Ashwini I already have the method proposed by you.  It's quite lengthy.  The method given by Virendra Saxena seems ok.  I will surely try it.

I think you can use closed reflux system methods at APH 2005 book for COD determination.

actually we used  silver sulfate during prepraing the reagents of sulfric acid digestion for your sample to eliminate  the interferncewith Cl ions specially when you deal with seawater analysis or highly saline waste water.

please read this paper:

edgeanalytical.com/wp-content/uploads/Inorganic_SM5220.pdf

regards,

please see this discusiion it may help you:

Pre precipitation of chloride ions prior to COD analysis? - ResearchGate. Available from: https://www.researchgate.net/post/Pre_precipitation_of_chloride_ions_prior_to_COD_analysis2#58d8cb56eeae39e9c14857c2 [accessed Mar 27, 2017].