Updated: Continued Au separations with SiN-NP wafer #'s 1029 and 1030
Sarah and I did some more gold separations with 10, 20, 40, 50, 60, 80 and 100 nm Au particles. We used the “clean” water purchased from the medical center. Same as last time, we diluted the “as-bought” gold 3 parts to 1 and loaded each cell with 300 uL before pressurizing at 5 psi for 1029 and 1-3 psi for 1030. We tried to pass approximately 200 uL. The first separations generally took 10 – 30 s and by the end the separations required 5 minutes or more.
We started with water, then 10 nm Au, then consecutively higher particle sizes and finally came back to repeat the smaller sizes to show that the pores were still open.
I think everything looks great….except, the 10 nm particles don’t pass as well as the 20’s, but the 10’s were older and showed multiple size peaks in the DLS tests.
More importantly, the 20’s and 40’s produced S greater than one in the filtrate, which I believe is impossible. Sarah and I spent hours trying to make this go away. We tested the initial solution 3 times, before during, and after the filtrations. We did controls on the water, the filtered water passed through the membrane, and the water in different colored centrifuge tubes. We can’t make any sense of it. (SEE BELOW! WE MADE SENSE OF IT!)
Sarah measured the absorbance of our initial solutions after they sat for approximately 5 minutes in the green centrifuge tubes. For an unknown reason, the absorbance increased. Using these increased values which are appropriate because the filtrates were all stored in green centrifuge tubes, we got the following, updated plots:
So all is right with the world.