Electrochemical sensor based on carbon paste electrode modified with nanostructured cryptomelane-type manganese oxides for detection of heavy metals

A carbon paste electrode modified with nanostructured cryptomelane-type (potassium) manganese oxides was evaluated as new electrochemical sensor for the detection of heavy metal ions in aqueous media. The cryptomelane-type manganese oxides are nanofibrous crystals with sub-nanometer tunnels which provide excellent sites for ion-exchanges. The adsorptive stripping voltammetry (ASV) technique involves preconcentration of the metal ions into nanostructured cryptomelane-type manganese oxides under an open circuit, then electrolysis of the preconcentrated species, followed by a square-wave potential sweep towards positive values. Factors affecting the preconcentration process were investigated using lead ion as the model analyte. The voltammetric responses increased with the preconcentration time from 2 to 30 min, and also linearly with lead ion concentrations ranging from 50 to 1200 ppb. The detection limits of target metal ion were 10 ppb after 4 min preconcentration and improved to 1 ppb after 20 min preconcentration. The potential for simultaneous detection of lead, silver, and copper is also discussed.