Determination of Molar Substitution of γ-Hydroxypropyl Starch

A new class of hydroxypropyl starch, γ-hydroxypropyl starch (γ-HPS), is synthesized by using 3-chloropropanol as the etherifying reagent. Two independent procedures for the determination of the number of moles of alkylene oxide combined per anhydroglucose unit (molar substitution, MS) in γ-HPS are described. The feasibility of the Zeisel-gas chromatographic technique and colorimetric determination are testified, and especially in the second approach, the stability and accuracy of dehydration process are also investigated. The concentrated sulfuric acid dehydration oxidation is replaced with 2-iodoxybenzoic acid oxidation while retaining the same acid degradation and the same ninhydrin color reaction. Furthermore, the reliability and the range of application of the methods are tested by analyzing three samples of γ-HPS and unmodified starch derivatives, and the results indicate that values of MS are in good agreement with each testing method.