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

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

► A novel potentiometric titration method for carboxymethyl chitosan was developed.
► Simultaneous determination of DD, DS and the distribution fraction of –COONa.
► The effect of precipitate on the third inflection point was eliminated.
► Calculating formulas of the three parameters were proposed.
► The method is suitable for N-, O- and N,O-carboxymethyl chitosan.