A new method based on fiber-optic sensing for the determination of deacetylation degree of chitosans Original Research Article

A novel method for determining the degree of deacetylation of chitosan is described. This involves a two-abrupt-change of the refractive index of solutions. Principle of the method is that the sample reacts with excessive acid, and the excessive acid is measured by alkaline titration. The refractive index of an aqueous chitosan solution was monitored and recorded in the course of acid-base titration. This gives a titration curve having two inflexion points and the difference between the two points corresponds to the volume of base required to neutralize the ammonium groups. It was proved that flocculation did not interfere with the measurement. The method is found to be low-cost, precise, and easy to operate for industrial applications. The DD values of three chitosan samples obtained with this new method show good agreement with those yielded from 1H NMR. Such a mechanism of refractive index monitoring should open up a new application in the field of chitosanolytic enzymes, such as chitosanase, that are important in bioprocesses.