Additional evidence of the operational character of the lability of complexes of copper(II) with simple organic ligands

A fixed analytical window of observation, 5 μmol l−1 free copper and 100 μmol l−1 total copper, but methods different in nature, operation mode and time scale were applied, in parallel, at pH 6.50 and 16 °C, to solutions with copper complexes of very different thermodynamic stabilities. Ethylenediaminetetraacetic acid (EDTA), l-cysteine, l-lysine, l-proline and succinate were used as metal buffers. Chitin (batch and column modes), chelex-100 (column mode) and normal pulse anodic stripping voltammetry (NPASV, −0.3 V deposition potential) were used as techniques. A strategy, based on using the mass of polymer that provided uptake of free copper similar to that taken up by Pseudomonas syringae bacterial cells in absence of ligands, was used for all but NPASV methods. Flame atomic absorption spectrophotometry was used for metal detection. The lability of copper complexes with simple organic ligands showed a strongly operational character. The time scale of the physicochemical method used for the determination of lability was not the only parameter inherent to the method that influenced the extent of copper complex dissociation. The nature of both initial and competing ligands and the operation mode may also condition the speciation results.