The degree of deacetylation of chitosan: Advocating the first derivative UV-spectrophotometry method of determination

Abstract

The degree of deacetylation (DD) is increasingly becoming an important property for chitosan, as it determines how the biopolymer can be applied. Therefore, a simple, rapid and reliable method of determining the DD for chitosan is essential. In this report, the DD of chitosan was determined by nuclear magnetic resonance (NMR), linear potentiometric titration (LPT), ninhydrin test and first derivative UV-spectrophotometry (1DUVS). The DD was calculated on a per mol basis instead of on a per mass basis. This is important as the molecular weights of N-acetyl-D-glucosamine and D-glucosamine are different. By converting the mass of N-acetyl-D-glucosamine and D-glucosamine into mols and calculating for the percentage of D-glucosamine present in the chitosan sample, a more accurate estimation of the DD can be obtained. Of the four methods, there is good correlation between 1DUVS and NMR. The concentration of chitosan solution for 1DUVS analysis was standardised as 0.1000 mg chitosan per ml of 0.0100 M acetic acid solution. The presence of D-glucosamine was corrected for by a reference curve for N-acetyl-D-glucosamine. 1DUVS is easy to perform, sensitive and the interference of other contaminants to the results is minimal compared with the other three methods. Therefore, we advocate 1DUVS to be used as the standard methods for routine determination of DD of chitosan.