A stirring-related aspecific ion-exclusion effect in an ultrafiltration-aided protein-ligand binding study

The occurrence at 0.1-0.01 m ionic strength of an aspecific ion-exclusion effect at the membrane during ultrafiltrations through Amicon PM 10 and XM 50 membranes is demonstrated. The extent of this phenomenon was found to be related to the shear rate at the membrane surface and to the ionic strength. Concentrations were measured by isotachophoretic analysis. Because of this effect, the use of an internal standard component is strongly recommended in (ultrafiltration-aided) binding studies.