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Colorimetric determination of the molar substitution of 2-hydroxybutyl and related starch ethers
- Harry-O'Kuru, R.E., Moser, K.B., Gordon, S.H.
- Carbohydrate polymers 1992 v.17 no.4 pp. 313
- ethers, chemical reactions, calorimetry, corn starch, spectral analysis, hydroxylation
- The molar substitution (MS) of 2-hydroxyalkyl starch ethers, e.g. 2-hydroxybutyl starch, can be determined spectrophotometrically. The principle involves a dehydrative-hydrolytic generation of n-butyraldehyde from the 2-hydroxybutyl starch ether substituent in concentrated sulfuric acid. The resultant hydrolyzate containing the aldehyde and allylic species of the substituent is complexed with 2,2-dihydroxyindan-1,3-dione (ninhydrin) in bisulfite giving a colored complex the absorbance intensity of which can be determined by a spectrophotometer at 470 nm. From the maximum intensity observed the concentration of butyraldehyde in the sample is derived by interpolation on a standard curve. The percentage of 2-hydroxybutane in the sample is calculated by comparison of the concentration of substituent to that of the hydrolyzed starting material. The MS is then calculated from the per cent substituent.