Purification and Proof of Structure

Since polysaccharides do not occur pure, it is essential that they be purified before their structures can be determined. Unfortunately, much careful structural work, particularly methylations, has been done on 

Unfortunately, there are no specific tests for absolute purity of polysaccharides. A polysaccharide may be regarded as free from other polysaccharides if it may be separated by at least two suitable procedures into fractions each of which have the same physical and chemical properties. The principal methods for the fractionation of polymeric compoimds are listed below. Most of these are applicable to polysaccharides or glycoproteins. 

Distribution between immiscible solvents (inclusive of Craig 

Ultrafiltration through graded membranes (dialysis and electro- 

Methods depending on electrical charge (applicable to polymers 

---