New voltammetric methods for the determination of heavy metals using a montmorillonite modified carbon paste electrode

Abstract

A carbon paste electrode modified with the clay mineral montmorillonite (MM) has been used to develop methods for the voltammetric determinations of cadmium(II), lead(II), copper(II) and mercury(II). The CPE has been modified by a newly developed procedure by direct mixing of the clay mineral, swollen in 1M KCl solutions for 12 hours and dried at 100 °C with the carbon paste. The analytical methods are based on the ion exchange properties of montmorillonite (MM). Methodological parameters such as pH of the analyte solution, preconcentration time and dependence of the voltammetric signal on the concentration of the analyte are investigated; the influence of interferents is studied. The detection limits (3σ) are 160 ng l−1 for cadmium, 600 ng l−1 for lead, 430 ng l−1 for copper and 10 ng l−1 for mercury(II) applying a preconcentration time of 10 minutes. To show the applicability of the methods, environmental samples are investigated. Another topic of the work presented here is to model preconcentration of divalent cations under open circuit conditions. The applicability of a model described by Kalcher et al. is investigated with all ionic species in question. The results show that the congruence between experimental and modelled data is excellent. A comparison of equilibrium constants obtained from electrochemical experiments and calculated by the model and equilibrium constants obtained from batch experiments shows almost excellent correlation.