A study of the separation, enrichment and determination of trace amounts of Hg2+ synchronously

Abstract

A novel, simple and highly reliable method for the determination of trace amounts of mercury on a glassy carbon electrode (GCE) modified with a compound of crystal violet and multi-walled carbon nanotubes (CV⁺I⁻/MWCNTs) is reported. The principle of organic co-precipitation in solution was applied to the application of electrochemical analysis. First, the CV⁺/MWNTs modified electrode was immersed in solution with I⁻, CV⁺ and I⁻ to form an ion association complex (CV⁺I⁻) as the carrier by the following reaction. Hg²⁺ was added into solution, where it reacted with I⁻ to form HgI₄²⁻, then in the presence of CV⁺ an organic coprecipitator formed HgI₄²⁻·2CV⁺ by electrostatic adsorption. Finally, the HgI₄²⁻·2CV⁺ was adsorbed by the carrier CV⁺I⁻ onto the surface of the modified electrode by the principle of organic co-precipitation. Meanwhile, trace mercury could be detected on the CV⁺I⁻ and MWCNTs modified electrode (CV⁺I⁻/MWCNTs/GCE) by an electrochemical method. Therefore, preconcentration, separation and electrochemical detection of trace mercury were simultaneously and synchronously carried out. After optimization of the method, a linear response was obtained in the concentration range from 5.0 × 10⁻⁹ – 1.9 × 10⁻⁶ M, with a detection limit of 1.0 × 10⁻¹⁰ M. The modified electrode shows high selectivity, sensitivity and stability. This modified GCE does not present any significant interference from Cd²⁺, Cu²⁺, Ag⁺, Fe³⁺, Pb²⁺, Cr³⁺, Zn²⁺. No deterioration was observed in the electrode response during at least 3 weeks of successive measurements. The proposed method enables the separation, enrichment and electrochemical detection of trace mercury in aqueous solutions.