We have used the Minisart® SRP15 (sartorius) but the real hold-up volume is around 500uL and we have lost a lot of sample. We need other ones which have a lower real hold-up volume.
Maybe you should try high speed centrifugation (7-10k rpm) instead of filtration?
Thank you Andrzej for your prompt answer, but we need to use this kind of filters because of the complexity of the samples (they are extracts of intracellular contents). We use etanol 15% to precipitate all the protein and then centrifuge 5-10 times at 14k rpm until the no appearance of pellet. After that, we use this type of filters to eliminate all the compounds bigger than 0,2um in order to keep in good condition the HPLC column. We are looking for other filters, similar than this one, which hold-up volume were lower. Thanks anyway for your answer!!
So, maybe take a look at this site: http://www.sorbtech.com/catalog.aspx?family_id=12 they claim dead volumes of 5 uL for 3 mm filters. I don't know what pore sizes are.
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