I am experimenting degradation of polystyrene nanoparticle using TiO2 and I face higher final TOC values than initial TOC. I assume it is due to the generation of CO2 while mineralization. However it is not matching the literature since studies show a lower final TOC after degradation. Any comment is appreciated.
Hello,
since you are referring to TOC, I suppose that there was an acidification step removing CO2 and carbonate anions, such that indeed OC is measured. The TOC analyzer should certainly be able to measure the low-molecular weight products of polystyrene degradation. I would ask myself whether TOC is properly measuring the initial system containing nanoparticles. Typically, the TOC is calibrated against solutions having a low molecular weight. If applicable, I would try to check the calibration with nanoparticles/large molecules against low molecular mass standards.
Thank you for your comment Ms. Shelja Sharma
. I agree. However, I am doing the experiments with DI water and for each concentration, I prepare 2 vials analyzed 3 times each. I have prepared and analysed the same experiment 3 times by now but get similar results. TOC is not decreasing.
Mr Mikhail Borisover I am using Teledyne Apollo 9000, able to read 4 ppb concentrations. My initial concentration including PS gets a reading of around 4 ppm and I calibrate the machine regularly. Do you still think it will get a wrong result?
Hi, Ahmad Morid Khurami, well, in no way I may think about wrong results, I was just trying to figure out the reasons for the interesting phenomenon you observed. The question is how do you calibrate it. Here is our old experience: with other machines, we have used, apparently, potassium phthalate for OC calibration. What was a surprise for us when concentrations of nitro-substituted molecules or fulvic and humic acids in aqueous solutions with precisely prepared concentrations, were underestimated by the instrument calibrated by an ordinary reference material. It was an issue of incomplete combustion of our organics. From that case I have learned that sometimes different reference materials might need to be checked to verify the combustion completeness. Can you prepare a precise concentration of PS and that is what determined by the machine? Again, it is just a hypothesis...
Dont know why you chose TiO2 since it is a very small particle, try calcium carbonate, both precipated or ground.
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