I want to test the rejection efficiency of membranes that I have synthesized and to determine if they would be suitable for micro filtration.
The most widely used are polystyrene latex beads, available in wide range of sizes, from Sigma-Aldrich and several other sources - I found Spherotech by Googling.
I agree that latex beads for testing your synthesized membrane are suitable. You should be aware, however, that for defining your membrane with an exact removal rate (pore size) you will need to use specific test bacteria. E.g. for defining a "0.2 µm" membrane you need to use Brevundimonas diminuta under defined conditions. If your membrane will have passed this test, it is per definition a "0.2 µm" membrane, irrespective of the exact pore sizes and their distribution. For other pore sizes, e.g. for 0.1 and 0,45 µm, you need other test micro organisms.
In addition to the previous reply, I would like to add that most suppliers of polystyrene latex beads also offer fluorescent or colored beads. I have found these colored beads to work very well for these tests. The retention can be easily assessed by UV-VIS analysis and don't require the use of particle counters. Our work shows that latex beads give perfectly straight calibration lines with concentration and they allow very accurate determination of retention.
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