A NOVEL ASSEMBLY FOR PERFLUORINATED ION-EXCHANGE MEMBRANE-BASED SENSORS DESIGNED FOR ELECTROANALYTICAL MEASUREMENTS IN NONCONDUCTING MEDIA

A perfluorinated ion-exchange membrane-based sensor suitable for elect roanalytical measurements in electrolyte-free media is described, whic h is assembled following a novel design enabling an easier preparation procedure. It is fabricated by inserting the terminal portion of a wo rking wire electrode into a Nafion tubing of suitable diameter and wel ding the wire thus wrapped to the bottom of a cell body by an insulati ng epoxy resin. The remainder upper Dan of the working electrode is co vered by a Teflon tubing to avoid the electrical contact with the inte rnal electrolyte introduced into the cell body, which is equipped with a counter and a reference electrode. As a result of this configuratio n, the actual working-electrode surface is the wire circumference cont acted by the polyelectrolyte material at the bottom of the assembly wh ich is exposed to the sample. The performance of this sensor has been tested by cyclic voltammetry, amperometric monitoring and now injectio n analysis for the electroanalysis of a series of prototype analytes e ither dissolved in electrolyte-free water (hydrogen peroxide, hydroqui none, ferricyanide, iodide and blomide ions) or present in nitrogen at mospheres (triethylamine and oxygen). Detection limits for these analy tes have been estimated for a signal-to-noise ratio of 3, together wit h the corresponding ranges within which the responses display a linear dependence on the analyte concentration. The results obtained point o ut that the novel assembly is profitable only for the analysis in elec trolyte-free liquid samples, while for the analysis of gaseous atmosph eres, especially for flowing gases, ion-exchange membrane sensors prep ared by the more usual procedure based on the use of working electrode materials embedded into a moist polyelectrolyte membrane should be pr eferred.