Cationic starch is a modified starch in which some of the hydroxyl groups are replaced by quaternary ammonium groups, so it is also called quaternary ammonium starch. The degree of substitution refers to the percentage of the number of hydroxyl groups substituted by quaternary ammonium bases in the total number of hydroxyl groups.
The following methods can be used to determine the degree of substitution of cationic starch:
Ion-exchange chromatography (IEC): The cations in the cationic starch are adsorbed by resins with ion-exchange groups, and then eluted with different concentrations of salt solutions, and finally the concentration of cations in the eluent is compared with the total hydroxyl groups in the starch The degree of substitution can be calculated by comparing the concentration.
Iodine titration method: Dissolve cationic starch in acetic acid-iodic acid solution, add excess potassium iodide, oxidize the hydroxyl group to generate carboxylic acid, and make the remaining iodine react with the quaternary ammonium base to generate chloride ion and iodide ion . Then titrate the remaining iodine with sodium thiosulfate solution to determine the content of quaternary ammonium base, and then calculate the degree of substitution.
Nuclear Magnetic Resonance Spectroscopy (NMR): The ratio of the number of quaternary ammonium bases and hydroxyl groups in cationic starch molecules is determined by nuclear magnetic resonance to calculate the degree of substitution.
Beichao reminds you: Different measurement methods may have certain errors and scope of application, and the specific choice needs to be judged according to the actual situation.
