Voltammetric procedure for trace metal analysis in polluted natural waters using homemade bare gold-disk microelectrodes

Abstract

Voltammetric procedures for trace metals analysis in polluted natural waters using homemade bare gold-disk microelectrodes of 25- and 125-μm diameters have been determined. In filtered seawater samples, square wave anodic stripping voltammetry (SWASV) with a frequency of 25 Hz is applied for analysis, whereas in unfiltered contaminated river samples, differential pulse anodic stripping voltammetry (DPASV) gave more reliable results. The peak potentials of the determined trace metals are shifted to more positive values compared to mercury drop or mercury-coated electrodes, with Zn always displaying 2 peaks, and Pb and Cd inversing their positions. For a deposition step of 120 s at −1.1 V, without stirring, the 25-μm gold-disk microelectrode has a linear response for Cd, Cu, Mn, Pb and Zn from 0.2 μg L⁻¹ (1 μg L⁻¹ for Mn) to 20 μg L⁻¹ (30 μg L⁻¹ for Zn, Pb and 80 μg L⁻¹ for Mn). Under the same analytical conditions, the 125-μm gold-disk microelectrode shows linear behaviour for Cd, Cu, Pb and Zn from 1 μg L⁻¹ (5 μg L⁻¹ for Cd) to 100 μg L⁻¹ (200 μg L⁻¹ for Pb). The sensitivity of the 25-μm electrode varied for different analytes from 0.23 (±0.5%, Mn) to 4.83 (±0.9%, Pb) nA L μmol⁻¹, and sensitivity of the 125-μm electrode varied from 1.48 (±0.7%, Zn) to 58.53 (±1.1%, Pb  nA L μmol⁻¹. These microelectrodes have been validated for natural sample analysis by use in an on-site system to monitor Cu, Pb and Zn labile concentrations in the Deûle River (France), polluted by industrial activities. First results obtained on sediment core issued from the same location have shown the ability of this type of microelectrode for in situ measurements of Pb and Mn concentrations in anoxic sediments.

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