Determination of degree of substitution for N-acylated chitosan using IR spectra

Abstract

Chitosans with various degrees of deacetylation (D.D.), which were used as standard sample for FTIR determination, were prepared from completely deacetylated chitosan by homogeneous N-acetylation reaction. By combining four probable probe bands, i.e. 1655, 1560, 1380 and 1320 cm⁻¹, eight probable reference bands, i.e. 3430, 2920, 2880, 1425, 1155, 1070, 1030 and 895 cm⁻¹ and two baseline methods, the most suitable ratiosA _{probe band}/A _{reference band} from IR spectra to determine the degree of acetylation of chitosan were evaluated from 48 combinations to beA ₁₅₆₀/A ₂₈₈₀,A ₁₅₆₀/A ₂₉₂₀ andA ₁₆₅₅/A ₃₄₃₀(A ₁₅₆₀/A ₂₈₈₀ is mostly recommended). The second baseline method, i.e. linking between adjacent two valleys, was better for measuring the absorbances of 1560 and 1655 cm^?1 bands. The determination range of the D.D. (1%–100%) covered almost the whole range. The standard curves withA ₁₅₆₀/A ₂₈₈₀ andA ₁₆₅₅/A ₃₄₃₀were also suitable for the determination of degree of substitution of other N-acylated chitosan, such as N-propionyl chitosan, N-butyryl chitosan and N-hexanoyl chitosan.