Purification and Concentration by Ultrafiltration

  • Paul Schratter
Part of the Methods in Molecular Biology book series (MIMB, volume 244)


Membrane ultrafiltration (UF) is a pressure-modified, convective process that uses semipermeable membranes to separate species in aqueous solutions by molecular size, shape, and/or charge. It separates solvents from solutes (i.e., the dissolved species) of various sizes. The result of removing solvent from a solution is solute concentration or enrichment. Repeated or continuous dilution and reconcentration are used to remove salts or exchange solvent (in such applications as buffer exchange). Definitions of some terms used in UF are given in Table 1.
Table 1

Some Definitions of Terms Used in UF


Enrichment of a solution by solvent removal.

The relative amount of a molecular species in a solution, expressed in percent.

Concentration polarization

Accumulation of rejected solute on the membrane surface; depends on interactions of pressure, viscosity, crossflow (tangetial) velocity, fluid flow conditions, and temperature.

Cutoff (MWCO)

The molecular weight at which at least 90% of a globular protein is retained by the membrane.


Irreversible decline in membrane flux because of deposition and accumulation of submicron particles and solutes on the membrane surface; also, crystallization and precipitation of small solutes on the surface and in the pores of the membrane, not to be confused with concentration polarization.


The solution passing through the membrane, containing solvent and solutes not retained by the membrane.


The fraction of solute held back by the membrane.


The solution containing the retained (rejected) species.


Amount of species recovered at the end of the process as a percentage of the amount present in the sample

Source:Courtesy of Amicon, Inc.


Critical Micelle Concentration Concentration Polarization Membrane Fouling Buffer Exchange Solute Recovery 
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Copyright information

© Humana Press Inc., Totowa, NJ 2004

Authors and Affiliations

  • Paul Schratter
    • 1
  1. 1.Millipore CorporationBedford

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