A form of *chromatography
in which the mixture to be separated is washed through a column packed with beads of an inert gel. The polymer forming the gel contains internal pores, into which molecules below a certain size can penetrate. In general, large molecules, which cannot penetrate the pores, move quickly down the column; smaller molecules, which enter the gel, travel more slowly. The technique exploits differences in size (i.e. molecular weight) and measurements of the rate of travel can give estimates of molecular weight. It is used particularly to separate protein mixtures, but can also be applied to cell nuclei, viruses, and other large molecules. It is sometimes referred to as molecular-exclusion chromatography.