Characterization of deacetylated chitosan and chitosan molecular weight review

Starting from a chitosan sample with a degree of deacetylation of 71%, thre e separate sample sets were generated by successive deacetylation and reace tylation processes. The degree of deacetylation of samples was determined b y UV spectrometry supported by thermogravimetric analysis. The molecular we ight of chitosan samples was determined in a solvent system of 0.25 M CH3CO OH/0.25 M CH3COONa, using viscometry and gel permeation chromatography (GPC ) with a TSK-gel column. The first set of samples had a similar degree of d eacetylation (DDA) but differing molecular weights. The second set of sampl es had a similar molecular weight but differing degrees of deacetylation. T he Mark-Houwink-Sakurada constants used for the determination of viscosity average molecular weight and the universal calibration of the GPC system we re K = 1.40 x 10(-4) dL/g and a = 0.83. Results showed that molecular weigh ts determined from both techniques are in good accord only at lower degrees of deacetylation. This may be attributed to the fact that the chemical str ucture of chitosan samples could have been largely altered with increasing or decreasing degree of deacetylation. Nevertheless, the trend with which t he molecular weights vary with the deacetylation time is consistent over a limited DDA range. A literature review of molecular weight analysis of chit osan is included.