Determination of the degree of substitution of acetylated starch by hydrolysis, 1H NMR and TGA/IR

The suitability of TGA/IR method for the analysis of the degree of substitution (DS) of acetylated starch (SA) was assessed. Ten standard samples were analysed for their DS by hydrolysis method and, those of the standards which could be properly dissolved, also by 1H NMR. NMR analysis shows as well that the standards had other structural differences than DS. By TGA using derivatives of thermograms (DTG) it was possible to predict the DS with percentual coefficient of determination of 98. Somewhat more accurate results (R2=98.7) were received when the evolving acetic acid was analysed by IR. The result is very good because it is at the same precision level as the results of the hydrolysis and 1H NMR methods.