Adsorption of trace metals from sea-water onto solid surfaces: analysis by anodic stripping voltammetry

Abstract

The rates and equilibria of the adsorption of dissolved Cd^II, Pb^II and Cu^II(at concentration levels of 2 × 10^–8 and 8 × 10^–8 mol l^–1) from sea-water and from a 0.55 mol l^–1 NaCl model solution onto electrochemical glass and quartz cells and Nalgene [fluorinated ethylene–poly(propylene)] sample bottles with and without added glass beads at pH 6.2 and 8.1 were measured by differential-pulse anodic stripping voltammetry. Lead(II) shows higher adsorption than Cu^II, whereas no adsorption of Cd^II is observed. Nalgene is the most suitable material for samplers and storage bottles, whereas quartz is the best material for the electroanalytical vessels. The maximum surface covering concentrations of Pb^II, (Γ_∞)(from sea-water at pH 8.1) on the surfaces of a quartz cell, a glass cell, a Nalgene bottle and glass beads were found to be 2.0 × 10^–11, 3.1 × 10^–11, 2.0 × 10^–12 and 2.6 × 10^–11 mol cm^–2, respectively. The maximum Pb capacities of the glass and quartz cells with the electrode assembly were calculated to be 2.3 × 10^–9 and 1.5 × 10^–9 mol, respectively. A procedure is proposed for the measurement of the trace metal capacity of the cell and the electrode assembly used in the experiments, for the determination of the metal concentration in natural samples.