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gel-filtration Column-chromatography technique, normally employing polymeric carbohydrate-gel beads of controlled size and porosity as a stationary phase. Mixture components are separated on the basis of their sizes and rates of diffusion into the beads. Smaller molecules tend to diffuse more rapidly into the beads, thereby leaving the mainstream of solvent and so becoming retarded with respect to larger molecules. This method can also be used to determine the molecular weight of an unknown substance.