Ultrafiltration (UF) is a pressure-driven, convective process that uses semipermeable membranes to separate species by molecular size and shape. UF is highly efficient, allowing for concentration and desalting at the same time. Unlike chemical precipitation (such as with ethanol or phenol/chloroform), there is no phase change, which often denatures labile species. Protein, DNA, and RNA samples can be routinely concentrated with up to 99% recovery of starting material without the use of co-precipitants.
Merck’s pressure-driven UF devices are available in two formats: centrifugal filters and stirred cells.
Large-Volume Centrifugal Filters
Centrifugal filter devices are powerful tools for protein, DNA, and RNA concentration and desalting. Centrifugal concentrator devices are ideal for separating high and low molecular weight species in large volumes. Merck’s large volume centrifugal filter devices come preassembled and ready to use. Individual devices are available for processing up to 70 mL volumes. For larger volumes, multiple devices can be spun simultaneously. Spin times are typically measured in minutes. Learn more about large-volume centrifugal filters
Stirred Cell Ultrafiltration
Choose stirred cell ultrafiltration when your sample volume exceeds the capacity of a centrifugal device or when you need a more gentle method of processing than centrifugation.
Stirred cell devices have been successfully used to purify proteins from large volumes of solution since 1965. Merck stirred cells are designed for gentle, efficient concentration or purification of macromolecular solutions in volumes from 3 to 400 mL. One important advantage of stirred cells is that concentration can be combined with buffer exchange by diafiltration (a process in which the exchange buffer is gradually and continuously added in while the existing solution is filtered out).
Simultaneous diafiltration and concentration using a stirred cell provides the analyte of interest at a concentration and in a buffer that is amenable with additional purification steps or the chosen analysis/detection method. While the concentration of non-permeating species is increased during ultrafiltration and the retained fluid volume is reduced, the concentration of membrane permeating species such as salts and microsolutes remains unchanged. Learn more about stirred cells