Colorimetric determination of the molar substitution of 2-hydroxybutyl and related starch ethers

• Published in: Carbohydrate polymers Vol. 17; no. 4; pp. 313 - 318
• Main Authors: Harry-O'Kuru, R.E., Moser, K.B., Gordon, S.H.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1992; Elsevier Science
• Subjects: Applied sciences; calorimetry; chemical reactions; corn starch; derivatives; ethers; Exact sciences and technology; hydroxylation; Natural polymers; Physicochemistry of polymers; spectral analysis; Starch and polysaccharides; Colorimetry; Investigation method; Molecular structure; Starch derivative; Experimental study
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/0144-8617(92)90175-P

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.