Ultrafiltration refers to the separation of very small particles in a fluid using a membrane. The membrane porosity is very small, the size of large molecules. The membranes are organized by molecular weight cut off – MWCO in kiloDaltons – kDa. These ratings mean that >90 % of a molecule of known molecular weight is retained. Ultrafiltration is used to concentrate, desalt, or fractionate proteins, DNA, and other bio-molecules. It is recommended that the MWCO chosen should be 6 to 3 times smaller than that needed to be retained. So if you need to retain a 150kDa protein use the 30kDa MWCO membrane for tight retention or the 50kDa MWCO for faster flow rate. The user should be aware that other factors such as charge and 3D shape of the molecule affect the MWCO of the membrane.
There are several ways to use the ultrafiltration membranes. The membranes are available as centrifugal devices. Volume ranges for the centrifuge tubes with membranes are from 50ul to 60ml. The MWCO membranes are also available in a 96 well filter plate form. Two volumes are available, < 300ul and <900ul. The MWCO membrane can also be ordered as 16in x 25in sheets. Flow cartridges containing the membranes are also available for pilot volumes. GE Lifesciences, Pall, and Thermo Scientific are sources for these ultrafiltration membranes.