100K Microcon Hydraulic Permeability
I ran the same 100K microcon system through numerous pressure ranges and put together the spread of hydraulic permeability results.
These results show that the hydraulic permeability of the microcon membranes decrease with increasing pressure. Once I finished running the tests at these pressures I reran a test at 19.52psi (3800RPM) to see if we would get the same permeability having ran it at higher pressures already. What I found was that the permeability decresed with the second test (not shown on the plot above). The first time I ran it at 19.52psi I found the permeability to be 20.4632 (ul/min*cm^2*psi); the second time I ran the same membrane at 19.52psi I found the permeability to be 13.1154 (ul/min*cm^2*psi).
Mike – there appear to be two bars at each pressure. That is an artifact of the graphic program, right. Because you shouldn’t get exact duplicates.
yes it is an artifact of the graphic.
Mike – how many microcons were run to generate each data point? How long was each experiment run?
Also, given that you see a considerable decrease in permeability at 19 psi after the experiments, are we sure this is a function of running at higher pressures, or is it just a function of time exposed to the buffer? They were never run dry, correct?
If you are using the same device each time and it seems to degrade, then you don’t know if the effect you are seeing is from reuse or higher pressure.
Its also possible that the measurement has some uncertainty or error so that the difference between your two measurements at the same pressure might just be experimental variation.
I suggest that you run triplicates at four pressures and use fresh microcons for each run. Then repeat the experiment using the same devices at the same pressures. Each bar should be lower if the membranes are being compressed during the test, but the higher pressures should suffer more. If buffer exposure is the culprit, I suspect you’ll see a similar drop in permeability at all pressures.
You mentioned that you were going to intentionally dry a membrane overnight and test it because you accidently did this once and found no flow. Did you do this? This would confirm that the membranes are shipped with an impregnated wetting agent.