In general, you should select a MWCO that is 3 to 6 times smaller than the molecular weight of the protein or other species to be retained. If flow rate or processing time is a main consideration, choose a membrane with a MWCO at the lower end of this range (3x); if retention is the main objective, choose a tighter membrane (6x). These values should be considered a guide, as solute retention and selectivity can vary depending on many factors such as pressure, molecular shape, presence of other solutes, and ionic conditions. Due to their complex shape, proteins behave differently than nucleic acids, which are linear and flexible. For the latter, suitability of centrifugal device MWCO is correlated with fragment length range. Because linear nucleic acid molecules can be forced through many MWCO membranes regardless of size, effective retention by an ultrafiltration membrane will require a reduction in g-force. For maximal nucleic acid retention, Nanosep device speeds must not exceed 5,000 x g and for the other centrifugal devices a speed at the lower end of the recommended g-force range is recommended.
The 100K membrane has 10 nm nominal pore size and is suitable for Biomolecule/particles larger than 30 nm. Centrifugation with nucleic acids is recommended to be carried out centrifugation at the lower end of centrifugal force range