Determination of the average degree of quaternization of N,N,N-trimethylchitosan by solid state 13C NMR

A novel method in which the quaternary salt of chitosan, N,N,N-trimethylchitosan (TMC) was synthesized using dimethylsulfate as the methylant agent is described. Although the synthesis of chitosan quaternary salts has been reported extensively, there remains some uncertainty in determining the resultant average degree of quaternization, DQ ¯ , in the final products. Here we used CP-MAS 13C NMR spectroscopy, that was able to calculate the DQ ¯ from the acetate salt of TMC. Chitosan in three different morphological forms (powder, wet-gel and flake) yielded TMC with DQ ¯ = 40.1%; 24.7% and 20.8%, respectively.