Mercury film electrodes coated with negatively charged polymer films in speciation studies of trace amounts of lead

Abstract

Glassy carbon electrodes modified with Nafion or poly(3-thiopheneacctatc) and subsequently plated with mercury where used for lead spcciation studies in buffered (0.1 M Tris. pH 8) sodium chloride (0.6 M ) solutions. The complexing agents studied were nitrilotriacetic acid, ethqlenediamine, oxalic acid and the well known electrode 'foulant' huinic acid. Most measurements were performed with square wave anodic stripping voltammetry. Films of Nafion were spin-coated and heat-cured, and poly(3-thiopheneacetate) films were produced by base hydrolysis of electropolymcrized poly(ethy1 3-tliiopheneacetate). The results are, to a certain extent, supporting the permselective model which has been suggested for Nation modified electrodes. However, they d o not allow the conclusions that negative species in general are not sensed by these ionomer coated electrodes, because the negatively charged groups of the ionomers may compete successfully for metal cations with chelating agents forming labile species. The nonlabile, negatively charged lead-NTA, where hardly measurable at the polymercoated electrodes, and the lead-oxalate complexes were also to a certain extent excluded by the ionomers. The response of the Nafion-coated electrode to the positively charged lead-ethylenediamine complexes was in accordance with the earlier reported permselective properties of the polymer when the literature values of the stability constant were used to calculate the lead species distribution. At the poly(3-thiopheneacetate) film, the response to 1e:ad-ethylenediamiiie complexes were higher than to the lead-oxalate complexes, but not as high as one could have expected if charge dependent permselectivity prevailed. As a means to understand the partition of ligands between hulk solution and polymer film, stability conslants for the lead complcxes of these were determined at the polymer-coated electrodcs as well as at the bare mercury film electrode.

A Study of Nafion‐Coated Bismuth‐Film Electrode for the Determination of Zinc, Lead, and Cadmium in Blood Samples

“…On the other hand, DPSV experiments conducted with a Nafion film without a bismuth coating indicated that weak stripping peaks (much lower in height than that in the presence of bismuth film) were obtained for all three metal ions(see curve 1), which in accordance with the previous work on NCMFEs [20]. This could be explained by the fact that at pH 4.5 used in this work, the sulfonate groups in the Nafion film were negatively charged and, as a result, the polymeric membrane acted as a cation-exchanger facilitating the nonfaradaic preconcentration of metal cations [21,22]. Therefore, the presence of Nafion film leads to the increase in sensitivity on the NCBFE over the bare BFE.…”

Performance of Poly(styrenesulfonate)‐Coated Thin Mercury Film Electrodes in the Determination of Lead and Copper in Estuarine Water Samples of High Salinity

“…Hence, the present results indicate that the sensitivity of the ASV determination increases in the sequence TMFE < Nafion-coated TMFE < PSS-TMFE, which is in accordance with the determined voltammetric charge densities. Polymer coating may result in decreased diffusion transport specially at high thickness films, but there are a several examples of increased ASV sensitivity to heavy metal cations at negatively charged polymer coated MFEs, for relatively thin films (thickness of nm to mm) [2,18,26,27].…”

Polypyrrole Coated Mercury Film Electrodes for Sono-ASV Analysis of Cadmium and Lead

“…Several effective approaches have been used to improve the preconcentration step in stripping voltammetric analysis. These methods include the use of rotating disk electrode [3,4], combinations of stationary electrodes with¯owing solutions such as wall-jet con®gurations [5], microelectrodes [6], and ultrasound [7±9]. The use of ultrasound in electrochemistry has been exploited and is now emerging as a powerful technique in electroanalytical chemistry [10±12].…”