COMPLEX EQUILIBRIA IN THE SYSTEM M2-POLYGALACTURONIC ACID (PECTIN) - H2O (M=CO, NI, CU, ZN, CD AND PB)()

Ionisation constants for polygalacturonic acid (pectin) were determine d by pH-metric titration in aqueous solution at different temperatures (283, 293, 303 and 313 K) and ionic strengths (0.1, 0.5, 1.0, 1.5 and 2.0), maintained with NaNO3. Complexing of pectin with Co2+, Ni2+, Cu 2+, Zn2+, Cd2+, and Pb2+ under the same conditions and M:L ratios of 1 :2 or 1:4 was studied. It was found that ML complexes prevail. Stabili ty constants were evaluated. Complexformation is a result of favourabl e entropy changes, whereas there is no significant change of enthalpy. The possibility of metal extraction by complex formation and ultrafil tration was examined. Selectivities in ultrafiltration and productivit ies of membranes for Cu2+ complexes of pectin were determined.