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

Abstract 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 –COONa 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 1 H NMR to be N,O-CM-chitosan, the method is suitable for the parameter determination of N-, O- and N,O-CM-chitosan.