Metal speciation by coupled in situ graphite furnace electrodeposition and electrothermal atomic absorption spectrometry

The technique of coupled in situ electrodeposition–electrothermal atomic absorption spectrometry (ED–ETAAS) is applied to the analytes Bi, Pb, Ni and Cu. Bi, Pb, Ni and Cu are deposited quantitatively from their EDTA complexes at Ecell=1.75, 2.0, 3.0 and 2.5 V, respectively (Ecell=Eanode−Ecathode+iR). By varying the cell potential, selective reduction of free metal ions could be achieved in the presence of the EDTA complexes. For Bi3+ and Pb2+ this utilised the voltage windows Ecell=0.6–1.0 and 1.8–2.0 V, respectively. For Ni, deposition at Ecell=1.7–2.0 V achieved substantial, but not complete, differentiation between Ni2+ (ca. 90–100% deposition) and Ni(EDTA)2− (ca. 12–20% deposition). An adequate voltage window was not obtained for Cu. The ability of ED–ETAAS to differentiate between electrochemically labile and inert species was demonstrated by application of both ED–ETAAS and anodic stripping voltammetry to the time-dependent speciation of Pb in freshly mixed Pb2+–NaCl media. Application to natural water samples is complicated by adsorption of natural organic matter to the graphite cathode.