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

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 E(cell)=1.75, 2.0, 3.0 and 2.5 V, respectively (E(cell)=E(anode)-E(cathode)+iR). By varying the cell potential, selective reduction of free metal ions could be achieved in the presence of the EDTA complexes. For Bi(3+) and Pb(2+) this utilised the voltage windows E(cell)=0.6-1.0 and 1.8-2.0 V, respectively. For Ni, deposition at E(cell)=1.7-2.0 V achieved substantial, but not complete, differentiation between Ni(2+) (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 Pb(2+)-NaCl media. Application to natural water samples is complicated by adsorption of natural organic matter to the graphite cathode.