Ultrafiltration

noun
1.
Physical Chemistry. a filter for purifying sols, having a membrane with pores sufficiently small to prevent the passage of the suspended particles.
2.
Mathematics. a filter in a topological space, having the property that no other filter exists in the space having among its subsets all the subsets in the given filter.
verb (used with object)
3.
Physical Chemistry. to purify by means of an ultrafilter.
noun
1.
a filter with small pores used to separate very small particles from a suspension or colloidal solution

ultrafiltration ul·tra·fil·tra·tion (ŭl’trə-fĭl-trā’shən)
n.
The filtration of a colloidal substance through a semipermeable medium that allows only small molecules through.