During my field study, I collected Groundwater samples and filtered them sequentially using 0.2um, 50kDa, and 3kDa. But when I analyzed these samples in the Shimadzu TOC analyzer, I got DOC concentration is high in 50 and 3 kDa in comparison to 0.2um.
E.g., in from sample
0.2um = 7ppm
50kDa = 16ppm
3kDa = 44ppm
How is it possible? Can anyone please explain?
Dear prof. Andersen,
Thank you for your reply.
It means my ultrafiltration membrane itself has organic carbon.
It‘s a theory. You can check by filtering a sample of pure water. I think your filter is made for protein seperation, so likely it isn’t designed for low TOC samples.
Dear Prof. Andersen,
I have already filtered ultrapure water(Resistivity >18.2 megaohm) through ultrafiltration(50 and 3 kDa); after analyzing the filtered samples, I got a high concentration of DOC, around 92 ppm.
I expected you would get higher DOC in ultrapure water. The reason is the polymeres that are used to make the functional part of the filter are not very stable and likely hardness and some salts strength contribute to the stability. You can improve by washing the filter with a mineral media before and perhaps add minerals to the sample (like CaSO2) before filtering. Since the filters are a bit expensive you might ask the supplier if they can recommend a procedure so you avoid loosing too much budget on trial and error.
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