DETERMINATION OF TRACES OF COPPER BY ANODIC-STRIPPING VOLTAMMETRY AFTER ITS PRECONCENTRATION VIA AN ION-EXCHANGE ROUTE AT CARBON-PASTE ELECTRODES MODIFIED WITH VERMICULITE

Vermiculite clay mineral, a novel modifier, was exploited to prepare modified carbon paste electrodes (CPEs), showing attractive ability to efficiently preconcentrate trace copper(II) prior to its voltammetric determination. Under open-circuit conditions, copper(II) was preconcentrated onto the surface of a modified electrode via the ion-exchange capability of the modifier. After medium exchange to a pure electrolyte solution (0.1 M NaNO3 + Britton-Robinson buffer, pH 5), the accumulated copper(II) was reduced at -0.7 V vs. Ag/AgCl during an equilibration period of 20 s and then determined by its re-oxidation employing square-wave anodic stripping voltammetry. The parameters and conditions such as pH of the analyte solution and supporting electrolyte, preconcentration time, CPE composition, its activation and regeneration, stripping mode and others, were studied in detail. The detection limit (3 sigma) of the proposed procedure was found to be 5 X 10(-9) mol l(-1) of Cu(II) in the analyte solution, for a preconcentration time of 10 min. Applying suitable preconcentration times, a linear calibration graph from 1 X 10(-8) mol l(-1) to 8 X 10(-5) mol l(-1) (0.6 mu g l(-1)-5.1 mg l(-1)) of Cu(II) was established. Multiple determinations (n = 10), following a preconcentration-measurement-regeneration cycle, gave a relative standard deviation of 4.9% at Cu(II) concentration of 5 X 10(-7) mol l(-1). The accuracy of the proposed method was checked by analysing a standard reference material (SRM 1643b).