Anodic Stripping Voltammetry at Mercury Films Deposited on Ultrasmall Carbon-Ring Electrodes

Anodic stripping voltammetry of lead and cadmium without deliberately added electrolytes has been studied at ultrasmall carbon-ring electrodes following In situ deposition of mercury. The stripping of lead has been studied In detail to Investigate the dependence of stripping peak current on experimental parameters such as potential scan rate, preconcentration duration, deposition potential, concentration of Hg⁺ during deposition, and concentration of Pb²⁺. Anodic stripping voltammetry In solutions without deliberately added supporting electrolyte avoids problems associated with Impurities Introduced when electrolyte Is added. These Impurities appear to be highly Important when Pb²⁺ analysis Is carried out In dilute solutions. In addition, a unique effect is observed when relatively low concentrations of Hg⁺ (1.0 × 10⁻⁶ M) are used for the In situ deposition step. When low Hg⁺ concentrations are used, the stripping current does not decrease as rapidly as expected as the concentration of Pb²⁺ is reduced. The slope of the log-log plot of peak current vs Pb²⁺ concentration is significantly less than unity, but the calibration plot Is linear, and the resulting enhanced peak currents at low Pb²⁺ concentrations make stripping analysis possible at extremely low concentrations. Concentrations as low as 3.2 × 10⁻¹¹ M of Pb²⁺ have been examined.