1,720,979 research outputs found
Porous electrodes supported on ion-exchange membranes for electrochemical detection in SFC
No full textA copper-phenantroline modified glassy carbon electrode for the amperometric determination of peroxides
No full textSviluppo di un elettrodo a mercurio supportato su membrana scambiatrice ionica per determinazioni mediante stripping anodico di metalli in tracce presenti in acque scarsamente saline
No full textA novel assembly for perfluorinated ion-exchange membrane-based sensors designed for electroanalytical measurements in nonconducting media
No full textA 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 Dan 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 now injection analysis for the electroanalysis of a series of prototype analytes either dissolved in electrolyte-free water (hydrogen peroxide, hydroquinone, ferricyanide, iodide and blomide 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
Porous electrodes supported on ion-exchanche membranes as electrochemical detectors for supercritical fluid chromatography
No full textA conveniently assembled electrochemical cell, exploiting a porous electrode supported on a moist perfluorinated ion-exchange polymer, is proposed for profitable electrochemical detection in supercritical fluid chromatography. It consists of a porous Pt working electrode, contacted by the mobile phase from the chromatographic column, which is chemically deposited onto one side of a Nafion membrane. The rear uncoated side of this membrane, acting as a solid polymer electrolyte, is contacted by an electrolyte solution (1 M NaCl) contained in an internal compartment equipped with a Pt counter electrode and a Ag/AgCl, Cl- 1 M reference electrode. Ferrocene, eluted with supercritical carbon dioxide through a Spherisorb column installed in a supercritical fluid chromatographic system, was used as electroactive prototype analyte to test the performance of this detector, which turned out to be quite better than that provided by a conventional on-line UV absorbance detector. The recorded peaks were characterized by both a good reproducibility (4.5%) and a linear dependence of their height and area, which extended over a wide concentration range (similar to3 orders of magnitude). Moreover, they were not interfered by possible solvent front, unlike peaks recorded by the UV detector. The detection limit, estimated for a signal-to-noise ratio of 3 (4.2 x 10(-11) mol), was lower by similar to1 order of magnitude than that found for the UV detector. Finally, the long-term stability of this detector was satisfactory in that only a similar to6% decrease in the current responses was observed after a rather long period (2 months) of continuous use
Amperometric determination of peroxides by glassy carbon electrodes modified with copper-phenantroline complexes
No full textAn amperometric sensor is described for the determination of peroxides in both aqueous and organic media. It consists of a rotating glassy carbon electrode modified by coating first with a thin film of a perfluorinated anionic exchanger (Tosflex) and then by immobilizing on this substrate the mixed-ligand copper complex [CuL(2)](2+) with 1,10-phenanthroline and bathophenanthroline (i.e., 1,10-phenanthroline containing two phenyl-sulfonic groups as substituents in the positions 4 and 7), thanks to the bonds formed between the -NR(3)(+) cationic groups of the Tosflex coating film and the -SO3- anionic groups present in the latter ligand. The modified electrode, which is rather stable with time and can be easily restored, permits detection of peroxides by their reduction at less cathodic potentials than at an unmodified electrode surface, It shows enhanced sensitivity in a variety of media (water, ethanol and ethanol-toluene 60/40 v./v.) which were investigated in view of their ability, on the whole, to dissolve peroxides originally present in different natural samples. Its satisfactory performance, which is unaffected by the presence of oxygen in the sample, in all the media studied is reported for hydrogen peroxide and tert-butyl hydroperoxide in terms of detection limits, dynamic ranges and response time. Its application to the direct determination of peroxides in some cereal oils was also attempted and the results found are compared with those obtained by conventional methods
Elettrodi supportati su membrane scambiatrici ioniche per la determinazione di inquinanti elettroattivi presenti in atmosfere gassose e acque scarsamente saline.
No full textUna semplice metodica per determinare il contenuto ionico in nano-volumi di campione mediante cromatografia ionica.
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