Simultaneous determination of degree of deacetylation, degree of substitution and distribution fraction of-COONa in carboxymethyl chitosan by potentiometric titration

摘要

A novel method for simultaneously determining the degree of deacetylation (DD), the degree of substitution (DS) and the distribution fraction of-COONa (δ_(-coona)) or-COOH (δ_(-cooh)) in carboxymethyl chitosan (CM-chitosan) was developed by potentiometric titration. The effect of precipitate on the third inflection point, a common problem in the previous method, was eliminated by integrated application of alkaline titration and acidic titration. Calculating formulas of DS, DD and δ_(-CONNAa) considering both the residues (GlcN and GlcNAc) and the carboxymethyl forms (-COONa and -COOH) were proposed. CM-chitosan products in different forms were examined to prove the reliability of the method. The standard deviation of DS, DD and δ_(_COONa) of Na salt CM-chitosan (n = 9) were 0.109, 3.51 % and 4.30%, respectively. As CM-chitosan was confirmed by IR and ~1H NMR to be N,O-CM-chitosan, the method is suitable for the parameter determination of N-, O- and N,O-CM-chitosan.