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Membrane Selection Guide

Apollo protein retention Molecular Weight Cut Off (MWCO) defines the smallest protein molecular weight which will be at least 90% retained in the retentate chamber.  Apollo protein concentrators are available with either 9k Da, 20k Da, or 150k Da MWCO ratings.

Maximum retention:

Higher retention of a given protein can be achieved by using a device rated for smaller proteins.  For example, a 150k Da protein will be retained more than 90% if a 20k Da MWCO device is used.


Fractionation of proteins by ultrafiltration based on difference in hydrated size (Stokes radius) is a challenging application. Protein-protein interactions and partial steric blockage of pores in the rejecting surface skin of the membrane by larger retained proteins determine the actual retention of the smaller component(s) of the mixture. For practical separation by ultrafiltration, a difference of at least 2 fold in Stokes radius is needed. This requires a difference of at least 8 fold in molecular weight. Other key variables are the concentration of the protein and the flow rate during the fractionation process. Predilution of the mixture to lower protein concentration, and use of a reduced rcf to lower flow rate, will minimize concentration polarization and resulting blockage effects and thus minimize rejection of partially-permeable components. Following fractionation, a smaller MWCO device can be used to rapidly reconcentrate the fraction(s).

General Guideline

Apollo MWCO

Typical Applications

9k Da

Desalting and concentration of proteins larger than 9k Da

20k Da

Desalting and concentration of 20k Da and larger proteins

150k Da

Removal of density gradient solute and smaller proteins from larger proteins, AAV & retroviral vectors

Apollo 90% MWCO ratings are determined with homogeneous purified proteins. Many factors can affect the retention of a specific protein, including concentration, ultrafiltration speed (relative centrifugal force), buffer composition and ionic strength and the chemistry of the protein.

Page last edited 3/16/16