[mferris]

I am facing a bit of a technical problem in the lab.  I have a solution that contains particles that have a diameter of roughly 100 nm as well as enzymes that have a diameter of roughly 7 nm.  I need to separate the enzymes from the solution without removing the larger particles.  I've tried using a normal filter syringe, separating all of the solution and enzymes and then trying to recover the larger particles from the filter, but the larger particles just remain lodged in the filter and are not recoverable. Does anyone know a good technique to separate smaller molecules from a solution of larger molecules?  Thanks!

[Yggdrasil]

Centrifugation may be an option, though ultracentrifugation may be required for such small beads.  Another option could be to use a centrifugal filter unit with a very high molecular weight cutoff such that, the enzyme will pass through the filter, and you can collect the beads in the filter unit.  For concentrating viruses (also particles with ~ 100 nm size) from solution, PEG precipitation is often used, though I'm not sure how efficient this will be at completely removing the enzyme.

[Babcock_Hall]

Why not use gel permeation (size exclusion) chromatography with a gel of the appropriate pore size?