Desalting of chitin derivatives by the electrodialysis via ion-exchange membranes

Using an electrodialysis technique, chitin derivatives in aqueous solutions containing various salts were desalted. The anodic cell (Part A: 0.1 mol/dm(3) KOH, 95 ml) and the cathodic cell (Part C: 0.1 mol/dm(3) HCl, 95 ml) were separated from the sample cell (Part O: 95 ml) by an anion-exchange membrane and a cation-exchange membrane,, respectively. The potential between the electrodes was regulated to 10 V (free current). Because N-acetylation of chitosan and N-deacetylation of chitin were respectively performed under acidic and strongly basic conditions unless enzymatic methods were not employed, neutralization in workup produced considerable amount of salt. Therefore, chitin derivatives such as partially deacetylated chitin (DAC) and partially acetylated chitosan (PAC) were sometimes contaminated with various salts. Aqueous solutions of PAC and carboxymethylated DAC containing NaCl, AcONa or AcOH were desalted by the electrodialysis. In the case of the suspension containing AcONa and gels produced by N-acetylation reaction of chitosan with Ac2O in aqueous AcOH/MeOH, the electrodialysis of the sample suspension eliminated AcONa inefficiently. This problem was solved by the treatment of the sample suspension with a homogenizer for 1 or 2 min before the electrodialysis. Since chitin and its derivatives have received growing attention as biologically active substances, the electrodialysis method provides a convenient way for the preparation of salt-free samples of chitin derivatives. (C) 1999 John Wiley & Sons, Ltd.