Is it possible for WQ samples to be affected by manganese?–TC samples are coming back “unsuitable” and we’re stumped.
asked 27 December 2016 asked by Aguanina (420 points)
Usually when you have chlorinated the labs send you the bottles with thiosulfate. Does your lab send you bottles without or with thiosulfate?
Yes, sorry it took so long to reply. The bottles do have thiosulfate. And the listed analysis method is SM 9223B-2004. Thanks
Well this method is for E.Coli determination so with thiosulfate in your bottles you shouln't have chlorine left unless your chlorine concentration is higher than what the sodium thiosulfate can destroyed.
Yes, I understand--but what about the other comment below? What do you think about it? I am in the process of comparing well production data, filter backwash records and anything else that I can link to the timing of these unsuitable samples. In any event, I appreciate you taking the time to comment.
If you want to check for E.Coli with analysis method SM 9223B-2004., from what I found, samples with high iron or manganese in combination with hydrogen sulfide may lead to atypical results and lab usually reject those results. There is few interference with the method. If your lab don,t know they should call their reagent supplier. As for your question about the comment below, I agree with water-witch, some method for chlorine determination can be affected by manganese.
Yes, manganese will interfere with a free chlorine residual even when sodium thiosulfate is present in the bottle. Depending on which method and testing equipment your lab is using, they need to account for the presence of manganese. When manganese is present then you need to use the Hach method 10241 ( assuming they are using a Hach method). This method is for the determination of residual free chlorine in the presence of manganese, chloramines, and other oxidants. all of which interfere with the DPD colorimetric, DPD titrimetric and amperometric methods for free chlorine residual. We have to do this at our plant, as we use chloramines as our secondary disinfection process. I am not familiar with other methods as we do not use anything else. I hope this helps.
Thanks for your reply--sorry it took so long for me to answer. The listed method is SM 9223B-2004. Does this clarify anything? I'll certainly ask the lab about this. Thanks again.