Biomedical Engineering Reference
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100
90
80
R90 value:
30 kDa
Membrane
selectivity
profile
70
60
50
40
30
20
10
Θ=
Membrane efficiency
0
1
10
100
1000
MWCO (kDa)
Figure 6.3. Membrane selectivity profile for determining MWCO.
of species. The membrane, concentration of the solute at the membrane surface, and to a
lesser extent permeate flux and tangential flow velocity also influence the retention.
To aid in initial membrane selection, manufacturers providemolecular weight cutoff
(MWCO) ratings for their membranes. The MWCO is often specified based on the R90
value that corresponds to a MW that is 90% retained by the membrane (Fig. 6.3). The
MWCO is generally determined using dextran and is merely an approximation to actual
solute retention.
As shown in Fig. 6.4, the shape of the membrane selectivity profile and MWCO
rating varies significantly between membrane manufacturers. The more vertical
the profile, the better the performance since more of the unwanted lower MW species
Figure 6.4. Membrane selectivity profiles for 10 kDa PES membrane from three manufacturers.
 
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