Methanol is usally added to comply with this, however, it has a great effect on the TOC of model pollutants.
There are several AOP prcesses (UV, UV/H2O2, Fe/H2O2, electro Fenton, photo Fenton). Which one you are referring to is not clear at this moment. I hope you are using H2O2. In that case, you have to remove residual H2O2 in the sample. There are several quenching agents including catalase, sodium hypochlorite, sodium thisulphate, etc. But which one you use depends on the nature of the organics present in the sample. Essentially, the method that you choose to quench H2O2 should not interfere with your TOC content. One of the simple method is heating or addition of KI. You should also consider the reaction of quenching agents with the chemicals that you use in TOC testing procedure. You need to experiment and find out the best one to suit your need.
When applying AOPs I normally add sodium thiosulfate (some crystals or few microliters of a concentrated solution) to the vials where sample aliquots for TOC and/or HPLC analysis are going to be collected.
Hope this helps
Can these (Sodium hypochlorite, thiosulfate, heating, KI etc) be used to stop fentons reaction too ??
Fenton reaction is typically the oxidation of ferrous ions from hydrogen peroxide to ferric ions. As long as the Fenton reaction is ongoing (i.e. both of the aforementioned reagents are still available in your solution) and you chose to terminate it you may surely add an appropriate amount of your selected quencher, bearing in mind that its addition will not interfere with your subsequent analysis. For instance you van either add a few drops of a concentrated solution of thiosulfate or use catalase which is very selective for H2O2 elimination; in the latter case, however, you should make sure (i) you adjust the sample pH between 6 and 8 (catalase decomposes otherwise) and (ii) the amount that you will add does not interfere with the COD or TOC measurement. However, if one of your reagents is the limiting factor (e.g. all ferrous has oxidized to ferric ions or all hydrogen peroxide has been consumed) then no quenching is necessary-the reaction has ended and from my opinion even there is some H2O2 available it will not make any significant difference to analyze it within 1hr of sampling.
I agree with Theodora. However, iron (III) could be photoreduced to Fe(II), so if there is still some H2O2 in solution the Fenton (photo-Fenton) reaction would continue. May be in this case samples should be prevented from light (collecting them in brown bottles for example). On the other hand, I would never use sodium hypochlorite (an oxidant) as a quenching agent.
Although I agree with Eva and most of the methods proposed, some of these reagents are expensive or can contaminate your samples. Concerning specifically Fenton reaction, you can keep it simple by adding sodium carbonate or diluted sodium hydroxide up to pH 7...
Sure, Juan! ...and filtering the samples before their analysis to remove Fe(III) hydroxydes
I worked on total petroleum hydrocarbons (TPH) removal by electro-Fenton process and added sodium thiosulfate in order to quench H2O2 after electro Fenton reaction. This quencher agent had no adverse effect on TPH analysis in my work. Moreover I had seen other researcher reported using of MnO2, KI, Na2CO3, NaOH, catalase, sodium hypochlorite as a quencher agent.
I hope this help you.
@ Dr. Giannakis, The TOC analysis is not disturbed by H2O2 so there is no need for destruction in UV/H2O2 experiments.
I think the use of few mL sodium bisulphate is recommended in quenching hydrogen peroxide because the reaction proceeds even after removal from the reactor.
increase the pH up to 10 or use some µL of methanol, thiosulfate or soudium hypochlorite.
I hope this help you.
You did not mention type of AOP used.
1) For fenton based AOP, i would recommend sodium sulfite. this link might prove useful to you.
Experiment Findings Residual Peroxide from Fenton process and a study to evaluat...
You should adjust pH to 10, precipitate out the iron then add in sodium sulfite to quench the residual H202. i would also recommend then adjusting the pH of the supernatent to an acidic pH (pH 3) due to the fact that the carbon dioxide in Air will dissolve into the solution to form carbonic acid. this will mess with the calculation of TOC, (since TOC=TC-IC).
2) For other ozone based AOP, the same quencher can be applied. Again i would suggest acidifying samples before testing for TOC.
Hello, my experience is not related to TOC but HPLC.
Each sample was urgently quenched with N2 gas for 5 min to stop the further reaction between IMI and ozone before the HPLC analysis. Since N2 is an inert gas, I think it would not affect TOC results. You can find further details from my paper.
Article Imidacloprid elimination by O3 and O3/UV: kinetics study, ma...
Best,
Busra S. Baghirzade
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