Choosing the Correct MWCO for Better Protein Recovery

Choosing the correct MWCO Once sample volume is determined, the next step is to select the appropriate MWCO (for ultrafiltration) or pore size (for microfiltration). MWCOs are nominal ratings based on the ability to retain > 90% of a solute of a known molecular weight (in Kilodaltons). The table below provides retention characteristics of different MWCO membranes for some solutes. For proteins, it is recommended that an MWCO be selected that is three to six times smaller than the molecular weight of the solute being retained. If flow rate is a consideration, choose a membrane with an MWCO at the lower end of this range (3X); if the main concern is retention, choose a tighter membrane (6X). It is important to recognize that retention of a molecule by an ultrafiltration membrane is determined by a variety of factors, among which its molecular weight serves only as a general indicator. Therefore, choosing the appropriate MWCO for a specific application requires the consideration of many factors including molecular shape, electrical charge, sample concentration, sample composition, and operating conditions. Because different manufacturers use different molecules to define the MWCO of their membranes, it is important to perform pilot experiments to verify membrane performance in a particular application. Common variables that increases molecule passage: • Sample concentration less than 1 mg/mL • Linear versus globular molecules • High transmembrane pressure created by g-force in centrifugal concentrators. (This is especially important in the case of linear molecules, for example DNA fragments. Decreasing the g-force can increase retention of molecules by a membrane.) • Buffer composition that favors breakup of molecules pH and ionic conditions that change the molecule (for example, cause conformational changes or aggregation) Common variables that decrease molecule passage: • Sample concentration higher than 10 mg/mL • Buffer conditions that permit molecules to aggregate • Presence of other molecules that increase sample concentration • Lower transmembrane pressure (in the case of centrifugal concentrators, lower g-force) • Adsorption to the membrane or device • Low temperature (4ºC versus 24ºC) Cytiva and the Drop logo are trademarks of Life Sciences IP Holdings Corp. or an affiliate doing business as Cytiva. Spartan is a trademark of Global Life Sciences Solutions USA LLC or an affiliate doing business as Cytiva. © 2025 Cytiva For local office contact information, visit cytiva.com/contact CY50926-17Mar25-AR cytiva.com Request sample MWCO selection for protein applications MWCO Membrane nominal pore size* Biomolecule size Biomolecule molecular weight 1K – – 3K – 9K 3K – – 9K – 30K 10K – – 30K – 90K 30K – – 90K – 300K 100K 10 nm 30 – 90 nm 300K – 900K 300K 35 nm 90 – 200 nm 900K – 3000K MWCO selection for virus applications MWCO Membrane nominal pore size* Virus or particle diameter 100K 10 nm 30 - 90 nm 300K 35 nm 90 - 200 nm MWCO selection for nucleic acid applications MWCO Base pairs (DS) Bases (SS) 1K 5 – 16 Bp 9 – 32 Bs 3K 16 – 50 Bp 32 – 95 Bs 10K 50 – 145 Bp 95 – 285 Bs 30K 145 – 475 Bp 285 – 950 Bs 100K 475 – 1450 Bp 950 – 2900 Bs 300K 1450 – 9500 Bp 2900 – 9500 Bs * Nominal pore size as measured by electron microscopy