Voltammetric picomolar determination of mercury, copper and cadmium using modified pencil graphite electrode with poly-L-cysteine and Fe3O4 nanoparticles.

Cost-effective simultaneous determination of mercury, copper and cadmium ions was performed by differential pulse anodic stripping voltammetry (DPASV) using a pencil graphite electrode (PGE) modified with poly-L-cysteine (P-L-Cys) and Fe3O4 nanoparticles. Electropolymerization of L-cysteine was performed by cyclic voltammetry (CV) through applying different cycles. Also, Fe3O4 was deposited in a single step by applying a constant potential on the electrode surface in the presence of ferric nitrate. To enhance the sensitivity of measurement, several parameters such as monomer concentration, scan rate, number of cycles in electropolymerization, ferric nitrate concentration, Fe3O4 electrodeposition potential and time, and pH of the sample solution were optimized. The surface morphology of the modified electrode was examined by SEM and FTIR. Electrochemical impedance spectroscopy was conducted to investigate the impedance of the electrode surface. The linear ranges for cadmium, copper and mercury were 0.001‒2500, 0.0002‒3600 and 0.0001‒2500 nM with detection limits of 6.4 × 10-13, 1.0 × 10-13 and 9.0 × 10-14 M, respectively. The stability and reproducibility of the electrode were investigated. Finally, the modified electrode was applied to determine mercury, copper and cadmium in real samples such as the groundwater, Caspian Sea and Tajan River water.