The introduction of Sephadex in 1959 heralded a new era in separation science. The concept of gel permeation chromatography (GPC) developed slowly and the key events leading to the discovery of Sephadex may be traced to Ingelman ?s early studies on the cross-linking of dextran, the subsequent patent by Flodin and Ingelman on the preparation of cross-linked gels and the exploitation of their gel filtration properties by Flodin and Porath.
Perhaps the most critical event was the synthesis of these gels in bead form with considerably improved flow rates, an innovation that led to the immediate acceptance of these gels in separation technology. Several types of Sephadex are currently available, each with a characteristic fractionation range. The most porous gel, Sephadex G-200, will fractionate proteins in the Mw range 4000–800000, whereas the upper limit for Sephadex G-25 is 5000. Although Sephadex gels are widely used for fractionation and purification of biopolymers, desalting constitutes one of the most important applications. In this context, desalting also refers to buffer exchange operations and the removal of low molecular weight impurities other than salts. Sephadex G-25 is now used for desalting or buffer exchange in many large scale operations. Insulin producers use Sephadex G-50 to remove proinsulin and protease impurities in the final stages of purification of porcine or bovine insulins.
The structure of Sephadex G-25 has recently been investigated by Holmberg (285) and the following novel structural features have come to light.
- Only 4% of the glucose units are cross-linked.
- Eight different structural elements were identified, including several glyceryl ethers of glucose and cyclic structures containing 1,4-dioxane rings. Two of these fragments are represented below 3 and 4.
- 80% of the beads consists of dextran.
