I am doing photodegradation experiments on Contaminants of Emerging Concern, and surprisingly I see an increase in TOC from the beginning to the end of the experiment! How this could be possible? Are we producing Carbon?
In both with contaminant and without contaminant this increase are observed. I am using both Humic standards and Effluent Organic matter.
I am using Shimadzu TOC analyzer to measure TOC with NPOC method.
Dear Emad,
On some occasions we have observed similar things. The most normal thing is that there is contamination and that during the analysis process the contamination is desorbed and this is what is giving these results...
Best,
Fran
Also do check if there are any pH changes to your reaction. The increase might also be attributed to dissolved CO2. If the interest of the study is on organics, it might be useful to acidify and purge dissolved CO2 to eliminate this effect.
While I do note that TOC measures organic carbon, the machine actually measures TOC as TC- IC. (total carbon minus inorganic carbon) this will sometimes introduce errors esp when changes to pH is observed. (at least that's what I observed)
Thank you for your response, Francisco Manuel Marquez .
The weird part is that this increasing is happening even when we do not have contamination in our samples. I am trying Humic Acid, Fulvic Acid, and NOM of Suwannee River and all of them have the same issue. Do you have any thought of that?
Thank you, Brandon Lee.
During the photodegradation process the pH increases less than one unit. Is that the reason? But how increasing the pH leads to increasing of carbon?
Do you mean if we want to keep the samples and then measure them by TOC analyzer, we need to acidify them? Because I do this too. I need more context if you don't mind?
Emad Sanei Hi, if the pH change is not that noticeable then it shouldnt be the case. There is some interference due to carbon dioxide/carbonate species with different pH Change. This results in some deviations (at least with that I noticed) if u were to acidify the samples, these deviations would be decreased. If the increase in TOC Is not that much, there might be errors in other parts of the experiments as others have suggested.
Dear, Emad,
Since you've observed TOC increase for your blank samples as well (correct me if I'm wrong), there are few possible reasons that should be considered:
1- the evaporation effects of Photo degradation
2- Degradation of reactor it self, based on its material. I have experienced the same using plexiglass reactors.
Feel free to contact me. Wish you best and happy new Year.
Dear Nelson J O’Driscoll . It could not be that. There is no bacterial growth since we immediately put our samples after the experiments. As far as I was able to find out, washing the reactors we do our experiments in and evaporation were the main reasons. But I still can see this increasing TOC in some experiments as well.
Hai Emad,
Have you got the reason? I had a similar experience with TOC analysis, which I figured out as the catalyst leaching. I was using a carbon based catalyst. I determined the reason by doing the same experiment in the absence of the emerging contaminant. You can think in this way too.
All the best
Jaimy
Jaimy Scaria Thank you so much for your reply. Can I have more context about your reason? I did the experiment without my contaminant, but I still see a little TOC increasing. It does not make any sense.
Emad Sanei , if your catalyst is carbon based, and its traces retained in your filtered samples, you may end up with a slight rise in TOC. In my case, these values were between 4-7 mg L-1. You can compare this scenario with yours. Carry out the optimum experiment in DDW with your catalyst system, and collect samples at same intervals (in the absence of target pollutant). Then you can understand is there any source of TOC present, other than the pollutant.
Jaimy Scaria Thank you so much. You are right but, in my case, I do not have catalyst in my system. It's just sunlight and contaminants in organic matter (both standards humic and effluent).
- Badges
- Science method