Revisiting the Determination of the Degree of Deacetylation Using Potentiometric Titration: A New Equation for Modified Chitosan

Abstract

Chitosan is a biopolymer that can be subjected to a variety of chemical modifications to generate new materials. The properties of modified chitosan are affected by its degree of deacetylation (DDA), which corresponds to the percentage of D-glucosamine monomers in its polymeric structure. Potentiometric titration is amongst the simplest, most readily available, and most cost-effective methods of determining the DDA. However, this method often suffers from a lack of precision, especially for modified chitosan resins. This is in large part because the equation used to calculate the DDA does not consider the molecular weight of the chemically modified monomeric units. In this paper, we introduce a new equation that is especially suited for modified chitosan bearing three different types of monomers. To test this equation, we prepared naphthalene-chitosan resins and subjected them to potentiometric titration. Our results show that our new equation, which is truer to the real structure of the polymeric chains, gives higher DDA values than those of the routinely used equations. These results show that the traditional equations underestimate the DDA of modified chitosan resins.

Keywords: chitosan; degree of deacetylation (DDA); determination of DDA of modified chitosan; naphtalene–chitosan derivatives; potentiometric titration.

Figure 1

Derivatization of chitosan with 1-naphtaldehyde.

Figure 2

Titration curve for the chitosan resin Napht-Chit-2a.

Figure 3

DDA values for all of the chitosan involved in this study as determined through potentiometric titration after calculation with Equation (17) (teal), Equation (2) (gray), and Equation (1) (blue).