Copper-binding efficacy of water-soluble chitosans: characterization by aqueous binding isotherms

The major objective of the study is to measure directly the isotherms of copper binding onto soluble chitosan preparations, using ion-selective electrode technique. Copper uptake is found to decrease strongly when chitosan acetylation degree or chitosan concentration increased. When relating the bound copper concentrations to content of non-acetylated amine groups in a chitosan, differences between copper uptake on different chitosan preparations become reduced but not disappear. Other effects, in addition to the contents of non-acetylated amine groups, can involve differences in the copper binding by different chitosans. Due to isotherm non-linearity, the distribution coefficient Kd of copper between a water-soluble chitosan and an aqueous solution may vary by two orders of magnitude as the free copper concentration Cfree varied. Linear relation between log Kd normalized by free amine group content of chitosans and log Cfree may help in preliminary estimating of the copper binding by water-soluble chitosans at a certain pH.