Stripping voltammetry of silver ions at polythiophene-modified platinum electrodes
Introduction
The polymer film deposition can be considered as one of the most versatile approaches for preparing chemically modified electrodes. The electropolymerisation of heteroaromatic compounds at electrodes surfaces has become one of the more effective ways to produce chemically modified electrodes with electrical conductivity. Among the various conducting polymers, polypyrrole (Ppy) is one of the most frequently investigated; it can be easily prepared by electrochemical oxidation of the pyrrole monomers [1] but the species loaded on a Ppy electrode surface containing chemically active counter-ions are difficult to remove resulting in poor reusability [2]. Wong at al. have reported the voltammetric extraction of silver species with Ppy film that had undergone a base–acid treatment but this was time consuming [3]. Song and Shiu found that silver species could be determined with Ppy film modified glassy carbon electrodes, but copper and mercury were also extracted onto Ppy film electrodes and caused significant interference in the determination of silver species. The Ppy electrode exposed to a binary mixture of silver and mercury showed only a large anodic peak at 0.53 V. According to the authors, this might be due to the reduction of both silver and mercuric ions at Ppy film to form the silver amalgam Ag(Hg) and simultaneous stripping of the two elements at the same potential during the anodic process [4]. Besides Ppy, the sulphur-containing polymers such as polythiocrown-ether, and poly-3-methylthiophene [5], [6] are mostly used as modifiers for heavy metal due to their high affinity for different species. Some analytical technique have been employed in metal analysis, such as atomic absorption spectrometry (AAS) [7], X-ray fluorescence [8], UV-spectrophotometry [9], inductively coupled plasma atomic emission spectrometry (ICP–AES) [10] and inductively coupled plasma mass spectrometry (ICP–MS) [11]. These techniques, commonly used for trace measurement of heavy metal in the laboratory, are not suitable for the task of in situ testing and monitoring. Electrochemical methods are between the most favourable techniques for the determination of heavy metal ions because of its low cost, high sensitivity easy operation and the ability for carry out speciation analysis.
In this paper, we present results of detecting Ag(I) at a polythiophene (PTH)-modified platinum electrode by an electrochemical controlled release of silver in 0.2 M KNO3 solution. This method features fast experimentation time, good suitability for field trace silver analysis and an acceptable electrode lifetime. Analytical performances of the method and the PTH/Ag interaction were investigated using cyclic voltammetry (CV), differential pulse anodic stripping voltammetry (DPASV), scanning electron microscopy (SEM) coupled to energy-dispersive analysis of X-ray (EDAX) and electrochemical impedance spectroscopy (EIS).
Section snippets
Reagents and materials
Thiophene (98%), dithizone, Nafion, 2,3-dibromthiophene, pyrrole, acetonitrile (HPLC grade) and tetrabutylammonium hexafluorophosphate (TBAHFP) were obtained from Aldrich (Steinheim, Germany). AgNO3, Cr(NO3)3, Cd(NO3)2, CuSO4, ZnCl2, FeCl3, Ni(NO3)2 and K2Cr2O7 were all purchased from Riedel de Haen (Germany). Supporting electrolyte KNO3 was from Panreac (Barcelona, Spain). All other chemicals used were of reagent grade. Solutions were prepared using deionised doubly distilled water with a
Cyclic voltammetry
Cyclic voltammograms of a modified electrode in absence of Ag(I), as well as those of a bare platinum electrode and a modified electrode, both in presence of Ag(I), were carried out. Neither the bare platinum electrode in presence of Ag(I) nor the modified electrode in absence of the ion, exhibited detectable peaks. On the other hand, when a modified electrode is dipped into a solution containing silver ion, a sharp anodic peak at around 0.15 V are observed. These results indicate the
Conclusion
The modified polythiophene platinum electrode proposed in this paper for the determination of ion silver shows good sensitivity and reproducibility and a great selectivity for Ag(I). Furthermore, it is of easy preparation, operation and regeneration, and can be used for more of 2 weeks of consecutive measurements. Its possibilities for field and on-site applications are being investigated.
Acknowledgements
We thank to the Agencia Española de Cooperación Internacional (AECI) for a grant to Hanane Zejli in the University of Cádiz, and to Mr. David Gómez, from the Institute of Polymer Science and Technology (CSIC, Madrid, Spain), for the SEM and EDAX results.
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