A study of copper and cadmium iminodiacetate complexes by ion-selective electrodes and application to cadmium monitoring

The chelating properties of the iminodiacetate ion (IDA2−) towards copper(II) and cadmium(II) were investigated through pM and pH measurements at constant ionic strength of 0.1 M and at 25°C in the pH range 4–9. The acidity constants founds were in good agreement with those already reported but significant differences from reported values were obtained for the stepwise copper complex formation constants, though the overall constant was in good agreement. Evidence is given for the existence of the protonated species CuH (IDA)−2, which proved helpful in explaining the anomalous complexing capacity of IDA in acidic medium. Practical application include the use of IDA for lowering the level of copper interference in monitoring cadmium ion with a cadmium-selective solid-state electrode; this provides reliable measurements which are otherwise impossible.