Comparison of physicochemical speciation procedures with metal toxicity to Chlorella pyrenoidosa. Copper complexation capacity

A comparison was made of methods for measuring the copper complexation capacity of natural and synthetic organic ligands in freshwaters. Complexation capacity values close to theoretical were obtained for nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid, when the following separation or analysis methods were used to detect ionic copper: algal assay (Chlorella pyrenoidosa), an aluminum hydroxide resin, ion‐selective electrode (ISE), and anodic stripping voltammetry (ASV) at the mercury film electrode (MFE) and Nafion‐coated MFEs. No complexation capacity could be measured for Cu‐NTA when the hanging mercury drop electrode (HMDE) was used. Results from the ISE and a resin with adsorbed aluminum hydroxide agreed closely with algal assay for the copper complexation capacity of solutions of fulvic acid and Fe‐humic colloids. Analysis by ASV at the HMDE, MFE, and Nafion‐coated MFE gave values‐of more than an order of magnitude lower than the other techniques because these methods failed to detect the end point for partially labile complexes with a large complexation capacity. On the other hand, the use of differential pulse polarography (DPP) detected these labile copper complexes and yielded results comparable with those for algal assay. Comparable copper complexation capacities for pristine river water samples were obtained by algal assay (2.5–4.1 × 10⁻⁶ M Cu) and DPP (2.0–3.7 × 10⁻⁶ M Cu), with lower values for the aluminum hydroxide resin (0.8–1.1 × 10⁻⁶ M Cu). Because the ASV techniques gave much lower results (0.1–0.4 × 10⁻⁶ M Cu), they are clearly unsuitable for the determination of the complexation capacity of freshwaters.