Sephadex

any of the synthetic derivatives of the polysaccharide dextran in which there is cross-linking to form a three-dimensional network with pores of a given size, that is, a molecular sieve. Sephadexes are produced in the form of granulated powder with particle sizes ranging from 20 to 300 micrometers and are classified according to pore size. Upon swelling in water or in salt solutions, sephadexes form gels, a two-phase system of the solvent within the granules and in the free volume. In chromatography, when columns are filled with sephadexes, large molecules are filtered more rapidly, being unaffected by the pores of the swollen gel; smaller molecules, however, become stuck in the pores and emerge only later. This filtering action accounts for the wide use of sephadexes in chemistry and biochemistry for the separation (fractionation) of mixtures of substances with molecular weights between 10² and 2 × 10⁵. Sephadexes are also used in determining the molecular weight of globular proteins and enzymes and in desalting and concentrating high-molecular-weight molecules. The inclusion of ion-exchange groups in sephadexes produces ion exchangers with a high fractionating capacity, which are used in the purification of biopolymers. Sephadexes are used in industry in the production of vitamins and antibiotics.