Too much sodium!

Yesterday, I ran another equilibrium dialysis with the same parameters but I doubled the number of spins to 20.

Today, I characterized the resultant nanoparticles, prepared new calibration samples, and ran all of the dialysis samples in the ICP. I diluted the nanoparticle sample to attempt to lower the concentration range the machine was reading. There were a few interesting results. Firstly, both this sample and the last sample are reading positive charges. The polymer coat is negatively charged so the only possible explanation is that the excess sodium (3:1 Na:S in the first sample and 6:1 Na:S in the second) is causing the surface to become positive. The very presence of an excess of sodium is counterintuitive, one would assume that the polymer would only absorb enough sodium to neutralize its charge. Going forward I will be doing more ICP and dialysis to get more data.