I wanted to know what do you mean by rejection ? In the next phase I will check the activity of both retentate and permeate, and my protein of interest which shows activity, should be present in either , retentate or permeate, but unfortunately I get activity in both, and thus assumes separation is not taking place properly. Which MWCO UF membrane will be suitable ? What about 10KDa? How the separations will take place and how the peptides will be distributed in the retentate and permeate?

Thank you so much I shall proceed in that manner.