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.
Two electrodes modified with either nickel or cupric hexacyanoferrate films were evaluated and compared as sensors for nonelectroactive cations in a flow-injection system. Both gave responses for group IA and ammonium ions, but only the electrode modified with cupric hexacyanoferrate was sufficiently stable for use in flowing solutions. This electrode responded t o K + , NH: , lib', and Cs+ ions rather selectively. Within this group, the selectivity could be controlled from general to almost specific toward Cs+ by the potential at which the electrode Was poised. The electrode was compatible with a mobile phase o f dilute nitric acid commonly used in ion chromatography, and chromatographic cieiection limits of 2 X h4 and linear responses over two decades were obtained. The electrode was applied to the ion chromatographic anal!.sis of K + and NH: in urine and K + in blood serum san1ples.
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