Catalase enzyme is frequently used to quench the residual H2O2 / OH radicals.

Alternatively, also sodium thiosulfate can be used.

Thanks dear Tero Luukkonen, in my case Catalase may not be of importance, and in case of Sodium thiosulfate problem of pH rise is crucial one,

Nevertheless so nice of you sharing your view :)

KI, i-PrOH and tert-BuOH any of these can be used as OH radical scavenger.

Great HO radical scavenger is also methanol in concetration higher than 0,01 mol/l.

If you don't observed complexation effect of humic acid, its can be used also. :)

"stop residual OH". Do you mean to remove OH from the solution after reaction has been completed?  If yes, you should not worry. The life time of OH radical is too short. It will not be present in your solution. It's not easy task to remove not reacted H2O2.  You may try to add dimethylsulfide . It should quickly react with H2O2 to form DMSO, but it may also react with Cr(VI)

H2O2 you can remove from solution with Na2SO3. Its guaranteed. :)

It's also guaranteed that Cr(VI) will be reduced by Na2SO3

Catalase is the obvious choice and it is very common for removing H2O2 in Fenton experiments. Unless the pH is so low it destroys catalase I cannot see any reason why you reject that suggestion by Tero Luukkonen.

Perhaps it would be relevant that you state the pH and what "the org. compound" is!

Dear Lukas, Dr Yuri is right, and that's the problem I am facing as my Cr(VI) also get reduced and completely vanished from sample, though I have alternative steps to determine Cr(VI), but I want to have sample with Cr(VI)+Org Comp. after H2O2 residual is quenched.

Yeah, it's right, but Na2SO3 its capable to reduce Cr(VI) only in strong acidic condition (Under pH = 2). How level of pH in acidic area have you in your system?

Well I have seen it reduced at pH 3, what could be the possible stoichiometric relation between Cr(VI) and Na2SO3  so that I might use minimum Conc./Vol of Na2SO3 to eradicate H2O2 and not reduce Cr(VI).

Maybe that's the way. You can try it. I'm curious about results. :)

Dr James! TBA is indeed a good OH scavenger, but it cant quench residual H2O2, and I have experimentally checked this fact, therefore there must be an additional step along with TBA to control residual H2O2 (Specifically).

sodium sulfite,sodium persulfate, Vc. You can try them, but to see whether there is interference for your reaction

I feel that there is some misinterpretation of the question.  As far as I understand the question is not how to scavenge HO-radical during the reaction, but how to safely remove a residual HO-radical and H2O2 AFTER the reaction. The life time of OH radical is too short. It is present in solutions  in a very low steady state concentration if it is continuously generated. The hydroxyl radical does not exist as a "residual" compound. The question is how to selectively remove  H2O2. Catalase seems to be ideal if the solution pH is adjusted after the reaction. 

Normal catalase doesn't work at pH 3 and adding sulfite or thiosulfate is likely to reduce Cr(IV). 

Still, I think it might be possible to remove H2O2 at pH 3 without losing Cr(VI), but in order to select a procedure you must state that the organic compound is and that you intend to do afterwards. Generally it is much easier to discuss experimental problems if the important parameters and concerns are included from the beginning.

Activated carbon can quench peroxide. Bisulfides can remove the peroxide but may reduce the Cr 6. Chlorine may also be used for quenching peroxide. 

Dear Najmul

I suggest that you can try alcohols like methanol, ethanol or t-butanol as a radical scavenger.  T-butanol would be the best choice . 

Regards,

Meysam

Hello

I suggest you tu use T-butanol, it's usually used as a radical scavenger .

regards