Endotoxin molecules tend to form micelles or vesicles in aqueous solution these can be removed from a solution by filtration. Ultra filtration (the process works by excluding endotoxin by molecular weight using an ultra-fine filter which blocks molecules of 10,000 Daltons or greater (the molar mass of an endotoxin monomer varies from 10,000 to 20,000 Da.). This process is often coupled with 0.1μm filter for bioburden control.
While effective for water, methods used for decontamination of water, such as ultra filtration, have little effect on endotoxin levels in protein solutions