Molecular weight manipulation of chitosan II: prediction and control of extent of depolymerization by nitrous acid

The molecular size of chitosan can be precisely modified by depolymerization with nitrous acid. The stoichiometry and specificity of the reaction, together with the simplicity of the reaction kinetics, provide the basis for derivation of a theoretical expression that relates the number-average molecular weight (Mn) of chitosan before and after depolymerization to the mass ratio of nitrous acid added to chitosan originally present. The simplicity of the expression and the lack of limiting assumptions in its derivation permits its use for the determination of the amount of nitrous acid required to degrade chitosan to a specified molecular weight or for the estimation of the Mn of high molecular weight chitosan. Optimized experimental conditions are identified for quantitative application of the method.