A novel assembly for perflorinated ion-exchange membrane-based sensors designed for electroanalytical measurements in nonconducting media

A perfluorinated ion-exchange membrane-based sensor suitable for electroanalytical measurements in electrolyte-free media is described, which is assembled following a novel design enabling an easier preparation procedure. It is fabricated by inserting the terminal portion of a working wire electrode into a Nafion tubing of suitable diameter and welding the wire thus wrapped to the bottom of a cell body by an insulating epoxy resin. The remainder upper part of the working electrode is covered by a Teflon tubing to avoid the electrical contact with the internal electrolyte introduced into the cell body, which is equipped with a counter and a reference electrode. As a result of this configuration, the actual working-electrode surface is the wire circumference contacted by the polyelectrolyte material at the bottom of the assembly which is exposed to the sample. The performance of this sensor has been tested by cyclic voltammetry, amperometric monitoring and flow injection analysis for the electroanalysis of a series of prototype analytes either dissolved in electrolyte-free water (hydrogen peroxide, hydroquinone, ferricyanide, iodide and bromide ions) or present in nitrogen atmospheres (triethylamine and oxygen). Detection limits for these analytes have been estimated for a signal-to-noise ratio of 3, together with the corresponding ranges within which the responses display a linear dependence on the analyte concentration. The results obtained point out that the novel assembly is profitable only for the analysis in electrolyte-free liquid samples, while for the analysis of gaseous atmospheres, especially for flowing gases, ion-exchange membrane sensors prepared by the more usual procedure based on the use of working electrode materials embedded into a moist polyelectrolyte membrane should be preferred.