Simple determination method of degree of substitution for starch acetate

To develop a simple method to determine the degree of substitution (dS) for starch ester, we prepared starch acetate with various dS values (0-3) and examined the mode of starch-iodine complex formation for the starch acetate by monitoring the ultraviolet-visible (UV-vis) spectra and their Fourier-t ransform infrared (FT-IR) spectral changes. The effect of acetylation on th e formation of the starch-iodine complex was investigated by monitoring the decrease in absorbance at 680 nm (blue value). The blue value decreased by increasing the standard dS value determined by NMR for starch acetate, but two different correlations between the blue values and the dS values were observed for the low- and highly-substituted starch acetate. The FT-IR spec tra for starch acetate particles were measured using a diffuse reflection m ethod. The peak areas and absorbances of the bands assigned to the acetyl g roup showed a poor correlation with standard dS values from the NMR. On the other hand, the FT-IR peaks assigned to sodium acetate produced by saponif ication of the starch acetate could be detected using the ATR (attenuated t otal reflection) method; they showed a good correlation with the standard d S values from the NMR. From these results, it was concluded that the ATR me thod should be available for the dS determination of starch acetate.