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Look into the 0.5 sq. m Millipore Pellicon ultrafiltration/ microfiltration devices (http://www.millipore.com/catalogue/module/ c558). They are moderately expensive, but the membranes are robust, reusable and allow fast concentration steps. We have regularly used them to concentrate cells (microfiltration mode) and/or media (ultrafiltration mode) from 16 L insect cell cultures to volumes of 500 mL in ~1 hr. Given the speed, you could use it for buffer exchange. Michael **************************************************************** R. Michael Garavito, Ph.D. Professor of Biochemistry & Molecular Biology 513 Biochemistry Bldg. Michigan State University East Lansing, MI 48824-1319 Office: (517) 355-9724 Lab: (517) 353-9125 FAX: (517) 353-9334 Email: [log in to unmask] **************************************************************** On Jan 4, 2009, at 8:34 PM, Michael Hothorn wrote: > Dear all, > > sorry for the non-CCP4 question. I am expressing a protein in insect > cells that is targeted for secretion into the medium. After > expression, I want to concentrate the medium containing my protein > of interest (from 10 l to 0.3 L) and at the same time change the > buffer to something that is compatible with my first ion exchange > chromatography step. I would be interested to know what kind of > ultrafiltration devices can be used for this purpose, and whether > some of you could suggest a quick, reliable and efficient system > that we could purchase for our lab. > > Thanks! > Michael >