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

Summary

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.