Sephadex:

Sephadex is available as a free-flowing powder consisting of regular bead from Pharmacia Fine Chemicals. While this is suspended in water, a bead swells. Drying and swelling of Sephadex is a reversible procedure. The material is capable of retaining its chromatographic behaviour after repeated drying and swelling. Sephadex is available in different types which differ in their degree of cross-linkage and, thus, the swelling properties. The several types are characterized through the letter G followed through a number. The range of the material available is Sephadex G - 10 to Sephadex G - 200. The numbers correspond approximately to the water regain value of the gel multiplied through a factor 10. In addition, there are special types of Sephadex known as Sephadex LH-20 and LH-60 that are intended for use along with polar organic solvents.

Sephadex is very chemically stable. Weakest points of attack within the structure are the glucosides linkages that are hydrolysed at low pH. It is stable in alkaline solutions. Its prolonged exposure to oxidizing agents may cause an increase in the carboxyl group content. The rise of carboxyl group within the structure impairs the chromatographic behaviour of the gel. It might be remembered that initially Sephadex contains an extremely small amount of carboxyl groups. That amount is so low in which most of the charge effects observed is attributed to Donnan effects caused through solutes.

Sephadex gels were the first for which a close relationship between molecular size and elution behaviour was observed. Within Sephadex series, there are gels available along with fractionation ranges distributed over an extremely wide interval of molecular masses. A few differences are evident in the fractionation properties of different group of substances. In most of the cases, these differences are relatively small and the general shape of the fractionation curves is similar.