Four different polymer-modified mercury film electrodes (MFEs) on a glassy carbon substrate were tested for their ability to determine lead and cadmium in the presence of surfactants. The polymers used for electrode modification were: Nafion, polyaniline, base-hydrolyzed cellulose acetate, and base-hydrolyzed poly(ethyl3-thiophene acetate). Triton X-100, sodium dodecyl sulfate, dodecyl pyridinium chloride, and bovine serum albumin were chosen as representatives of surface active compounds. It is shown that polymer-covered electrodes are useful in surfactant-containing media ,in some instances, but none of them remained unaffected by any of the four surfactants. The cellulose acetate electrodes seem to be less affected by proteins than the bare MFE and other modified electrodes. The Nafion and cellulose acetatecoated electrodes were used for the determination of lead in filtered and acidified, but otherwise untreated, water samples from a sewage treatment plant. The results obtained with the cellulose acetate-coated electrode were in good agreement with those from atomic absorption spectroscopy.
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.
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