Determination of the degree of the substitution of hydroxyethyl guar gum

An improved chemical method for the determination of the degree of the substitution of hydroxyethyl guar gum by mixed p-toluenesulfonic-acetic anhydride has been described. The hydroxyethyl groups are cleaved from modified galactomannans at 130 °C in the presence of excess mixed p-toluenesulfonic-acetic anhydride for 14 h, and then the products hydrolyzed into ethylene glycol at pH 11 for an hour. Quantifying the mass of reaction products derived from the hydroxyethyl group, the degree of the substitution of hydroxyethyl guar gum can be precisely estimated.