Gel filtration is a technique used for separation of proteins by molecular weight when passed  through the colums of gels. Several kinds to gels which have well defined pore size are employed. Materials such as synthetic resins, porous glass beads, agarose or sephadex are suspended in a suitable solvent. The polysaccharide gel, sephadex is commonly used, which when placed in water swells and forms an insoluble gel. The choice of gel is determined on the basis on the basis of the molecular weight of proteins. Sephadex allows small size protein molecule to pass through the column, while large-size particles are excluded.