Centrifugal Filters

Filtration devices can be used to concentrate small to large volume biological and environmental samples in preparation for downstream processing and analysis. Several filter properties should be considered in selection:

• MWCO or NMWL: In general, the molecular weight cut off (MWCO) or nominal molecular weight limit (NMWL) of the membrane filter should be one half to one third of the size of target protein for retention.

• Filter Material: Regenerated cellulose membranes have low protein adsorption and feature low extractables, supporting high sample recovery for protein and biological samples. Hydrophilic PVDF membranes exhibit very low protein binding and are used to clarify protein solutions. Hydrophilic PTFE membranes have high strength and are typically used in clarifying aqueous solutions. Polyethersulfone (PES) membranes offer high flow rates for faster filtration. Cellulose acetate membranes are hydrophobic and may require pre-wetting for use with aqueous samples. Nylon membranes exhibit higher protein binding but have higher chemical resistance and lower extractables.

• Working Volume: Centrifugal filtration devices have specified starting volumes, typically accommodating anywhere form 0.5 mL to 70 mL of sample. Pressurized filtration devices can accommodate larger volumes ranging from 50 mL to >400 ml.

• Final Volume: Many filtration devices utilize a dead stop technology to prevent drying out of sample. The final volume of the device can be used to determine concentration factor.