Determination of degree of substitution for N-acylated chitosan using IR spectra
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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 ratios A(probe) (band)/A(reference) (band) from IR spectra to determine the degree of acetylation of chitosan were evaluated from 48 combinations to be A(1560)/A(2880), A(1560)/A(2920) and A(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.B. (1%-100%) covered almost the whole range. The standard curves with A(1560)/A(2880) and A(1655)/A(3430) were 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.