Electrochemically Aided Solid Phase Micro‐extraction of Mercury(II) at a Poly(3‐Methylthiophene) Modified Gold Electrode

Abstract

A simple approach for increasing the sensitivity and selectivity for the detection of mercury(II) species in water is presented. The technique is based on two steps: (1) micro‐extraction (uptake step) of mercury(II) by simply incubating an electropolymerized poly(3‐methylthiophene) (P3MT) modified gold electrode, at open‐circuit potential conditions, into a solution containing the heavy metal for 30 min and (2) the electrode is transferred from the analyte solution to an electrochemical cell (release step) for successive voltammetric determinations. Surprisingly, cyclic voltammetric measurements showed a first large anodic peak characteristic of oxidation of metallic mercury to form mercury(II) at 0.53 V. The reversed scan, showed a smaller cathodic peak at 0.4 V, suggesting a possible electroless reduction from Hg(II) to metallic mercury during the extraction step probably caused by the heteroatom of P3MT. Under these conditions, differential pulse voltammetry (DPV) measurements performed on the P3MT electrode showed that the anodic peak current exhibit a good linear concentration dependence in the range 10⁻⁸–4 × 10⁻⁶ mol/L. The detection limit was estimated for S/N > 3 to be 10⁻¹⁰ mol/L. The analytical performances of the extraction method has been explored by optimizing the electropolymerization time, pH, and effect of interferences due to other ions. On the other hand, scanning election microscopy–energy dispersive analysis of x‐ray (SEM–EDAX) and electrochemical impedance spectroscopy (EIS) measurements performed on P3MT films confirmed the adsorption of the heavy metal on the polymeric film due to the extraction process.

Keywords:

• Electrochemical solid phase micro‐extraction
• Poly(3‐methylthiophene)
• Electroless reduction
• Mercury(II) determination

Acknowledgments

This project is supported by the Moroccan Ministry of Higher Education: PROTARSII P21/96 and PARS CHIM 044. We would like to thank Professor Leberato from the University of Seville for his kind help in performing SEM‐EDAX measurements.