Determination of degree of deacetylation of chitosan by 1H NMR spectroscopy

This paper describes a novel method to determine the degree of deacetylation of chitosan by 1H NMR spectroscopy. Measurements were carried out at 70°C by using 2 wt% CD3COOD/D2O and 2 wt% DC1/D2O as solvents for chitosan. In the case of DC1/D2O system, effect on hydrolysis of chitosan should be taken into consideration, and the pulse repetition delay required for 45° pulse is 40s. Whereas, in regard to CD3COOD/D2O system, 6s pulse repetition delay is enough for 45° pulse, and moreover, high magnetic field NMR apparatus is necessary, because signal of CD2H residue in CD3COOD overlaps with that of CH3 residue in N-acetyl residue and determination of the difference of two spectra is required. The proposed method is more effective, precise and simple, comparing with the conventional colloid titration and elemental analysis methods. Assignments of 1H and 13C NMR spectra of chitosan are also reported.