Chitosan Preparation and Characterization

Chitosan results from the deacetylation of chitin and it becomes soluble in aqueous acidic medium when the average DA is lower than 0.5. In fact, this limit depends on the distribution of acetyl groups along the chains. Chitosan fully deacetylated may be reacetylated in homogeneous phase. In these conditions, solubility is observed up to DA 0.6 due to a random distribution of the acetyl groups. 

DA from H NMR (liquid state) insoluble 0.58 0.21 acetyl traces 

The second important characteristic of these polymers is the molecular weight distribution and the average molecular weight as well as the intrinsic viscosity. The first difficulty encountered in the measurement of these values concerns the solubility of the samples and the dissociation of aggregates often present in polysaccharide solutions [48,49]. 

To avoid these artefacts, it was proposed that 0.3 M acetic acid/0.2 M sodium acetate (pH = 4.5) be used as solvent since there was no evidence for aggregation in this mixture [50]. At that time, it was demonstrated that the value of DA modifies the K and a parameters. In this solvent, the absolute M values were obtained from steric exclusion chromatography (SEC) equipped with online viscometer and light-scattering detector, allowing the Mark-Houwink parameters to be determined without fractionation and also the relation between the radius of gyration and the molecular weight. 

A more recent analysis of the molecular weight distribution by SEC using a triple detection (viscosity, concentration, molecular weight) has been described [51-53]. It was performed on heterogeneous chitosans, obtained from commercial sources after solid state treatment and 

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Shinya, Y., Tsnrnshima, H., Tsnrnmi, T., Kajiuchi, T., Kam, and Leong, W. Polyelectrolyte complex films derived from polyethyleneoxide—maleic acid copolymer and chitosan Preparation and characterization. Macromol. Biosci. (2004) 526-531. 

Y. Shin-Ya, H. Tsurushima, T. Tsuriuni, T. Kajiuchi, and K.W. Leong, Polyelectrolyte complex films derived from polyethyleneoxide-maleic acid copolymer and chitosan preparation and characterization, Macromol. Biosci., 4,526-531,2004. 

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