Mercury-free simultaneous determination of cadmium and lead at a glassy carbon electrode modified with multi-wall carbon nanotubes

A multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE) was described for the simultaneous determination of trace levels of cadmium and lead by anodic stripping voltammetry (ASV). In pH 4.5 NaAc-HAc buffer containing 0.02 mol/l KI, Cd²⁺ and Pb²⁺ first adsorb onto the surface of a MWNT film coated GCE and then reduce at −1.20 V. During the positive potential sweep, reduced cadmium and lead were oxidized, and two well-defined stripping peaks appeared at −0.88 and −0.62 V. Compared with a bare GCE, a MWNT film coated GCE greatly improves the sensitivity of determining cadmium and lead. Low concentration of I⁻ significantly enhances the stripping peak currents since it induces Cd²⁺ and Pb²⁺ to adsorb at the electrode surface. The striping peak currents change linearly with the concentration of Cd²⁺ from 2.5×10⁻⁸ to 1×10⁻⁵ mol/l and with that of Pb²⁺ from 2×10⁻⁸ to 1×10⁻⁵ mol/l. The lowest detectable concentrations of Cd²⁺ and Pb²⁺ are estimated to be 6×10⁻⁹ and 4×10⁻⁹ mol/l, respectively. The high sensitivity, selectivity, and stability of this MWNT film coated electrode demonstrated its practical application for a simple, rapid and economical determination of trace levels of Cd²⁺ and Pb²⁺ in water samples.