Speciation of copper(II) in natural waters in thepresence of ligands of high and intermediatestrength

A new procedure is presented for the determination of the ligands of copper(II) in natural waters, based on titration with the metal ion, monitored by measuring the concentration of copper(II) sorbed on the carboxylic resin Amberlite CG 50. The data are treated by the Ruzic linearization method to obtain the concentration of the ligands and the conditional stability constant of the complexes. Ligands with reaction coefficient (alfaM) higher than 0.1 K*w/V are detected, where K* is the ratio of the concentration of sorbed metal to the concentration of free metal in solution, which can be evaluated from the sorption equilibria of copper(II) on Amberlite CG 50, w is the amount of water in the resin phase, and V the volume of the solution phase. Some natural waters at high and low salinity were examined. The ligand concentration determined in these samples ranged from around 50 to 2000 nM, while the original copper concentrations from 11 to 130 nM. The ligand concentration was always much higher than that of copper(II). The conditional stability constants were very high, particularly in low salinity waters, where values as high as K′ = 10^(15.7) were obtained. In high salinity waters values around 10^(9) were found for the complex formation constant of the ligands titrated with copper(II). The investigation was also extended to a model solution, containing EDTA, obtaining K′ = 10^(15.5), in acceptable agreement with that evaluated from the literature values.