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

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 ratiosAprobe band/Areference band from IR spectra to determine the degree of acetylation of chitosan were evaluated from 48 combinations to beA1560/A2880,A1560/A2920 andA1655/A3430(A1560/A2880 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 withA1560/A2880 andA1655/A3430were 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.