Determination of total and free copper(II) and cadmium(II) in freshwater samples by chelating resin titration with a resin containing iminodiacetic groups

The sorption of copper(II) and cadmium(II) on a chelating resin containing iminodiacetic groups from freshwater samples by a batch procedure is investigated. As in most cases sorption is not quantitative, a method is suggested for the evaluation of total concentration, based on the determination of the concentration of the metal ion sorbed on the resin at different values of the ratio V/w, i.e. the volume of the solution phase to the amount of resin. The method is named chelating resin titration (CRT). A good agreement was found between the total concentration of the metal ion in the sample and that found by CRT. The ratio of total to free metal ion (alpha(M(I))) in solution in the presence of the resin could be evaluated by the same procedure, obtaining very high values at the two acidities considered, and for both metal ions. The usual complexing substances commonly present in freshwaters can not be considered responsible for such strong complexations