ANODIC-STRIPPING VOLTAMMETRY OF COPPER AT EXSITU-FORMED MERCURY-COATED CARBON-FIBER MICROELECTRODES IN THE PRESENCE OF LOW CONCENTRATIONS OF SUPPORTING ELECTROLYTE

The anodic stripping voltammetry of copper at ex situ-formed mercury-coated carbon fibre microelectrodes was studied in the presence of low concentrations of supporting electrolyte. Determinations can be carried out in the absence of a deliberately added electrolyte but are affected by changes in the ionic strength. The addition of a small amount of NaNO3 was found to increase the reproducibility in the determinations, particularly in the differential-pulse mode; 5 x 10(-10) M Cu2+ could be determined with a deposition time of 1800 s in the presence of 2.5 x 10(-6) M NaNO3. The stripping peak shapes and potentials also depend on the electrolyte concentration and this dependence cannot be explained by ohmic drop, migration or contamination effects. A dependence of the stripping kinetics on the electrolyte concentration, due to double-layer effects, appears to be a more likely explanation. The stripping peak currents also depend on the nature of the mercury film but this dependence is probably caused by supersaturation of the coatings. The dependence of the copper stripping peak currents on the deposition potential, deposition time, copper concentration and the stripping technique employed (pseudo-staircase, differential-pulse or square-wave stripping voltammetry) in the presence of low electrolyte concentrations is discussed. Some results for lead are also presented.