Analysis of cationic starches: determination of the substitution pattern of O-(2-hydroxy-3-trimethylammonium)propyl ethers

A method was developed to determine the substitution pattern of O-(2-hydroxy-3-trimethylammonium)propyl ethers of starch. As model compounds cationic cyclomaltoheptaose and cyclomaltooctaose were prepared. After cleavage of the glucosidic linkages by methanolysis and subsequent permethylation, the positively charged substituents were transformed to the neutral O-(2-methoxy)-2-propenyl ethers. These compounds could directly be separated by capillary GLC or after mild hydrolysis as the more stable O-(2-oxo)propyl derivatives. To halve the number of degradation products, the methyl glucosides could be reduced to the corresponding 1,5-anhydroglucitols. Results for two model compounds [degree of substitution (ds) 0.33 and 0.46] and three cationic starches (ds 0.02–0.05) are given.