Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

Binding of Pb²⁺ ions to magnesium pectinates was studied by dialyzation technique in relation to their esterification degree (E) in the interval E = 0 to 84,7%, at an ionic strength I = 0.30. It has been found that the binding of Pb²⁺ ions to pectinates proceeds according to the theory of multiple equilibria. The values of stability constant K and selectivity coefficient K^Pb_Mg evidence the high selectivity of pectinates towards Pb²⁺ ions. Both those constants are, in contrast with value corresponding to other bivalent cations (e.g.Ca²⁺, Sr²⁺), independent on the esterification degree of pectin in the E 50% range. A strong binding of Pb²⁺ to carboxyl groups takes place also at a high esterification degree of pectin. The exchange of Cr³⁺ 3 K⁺ was investigated with a model preparation of potassium pectate crosslinked with epichlorhydrin by a batch method at various pH of equilibrium solutions (I = 0.15). Potassium pectate was shown to be a highly selective ion exchanger towards Cr³⁺. The binding of Cr³⁺ to pectate also occured in a sufficient extent at a low pH of equilibrium solutions (pH 3). Due to a very strong binding of Cr³⁺ to pectate a substantial shift of dissociation equilibrium of carboxyl groups in favour of further binding of Cr³⁺ ions occured.