Ion-exchange voltammetry at polymer-coated electrodes: Principles and analytical prospects (original) (raw)
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Electrochemical studies on ion-selective polymer membrane electrodes
Journal of Membrane Science, 1985
The selectivity and response of neutral carrier based polymer membrane electrodes are investigated via exchange current measurements for systems containing valinomycin, dibenzo-18-crown-6, and plasticizer alone in a polyvinyl chloride matrix. Using a transient galvanostatic step method, apparent exchange current densities of 1.3 X 10m3 A/cm', 5.4 X lo-* A/cm2, and 2.2 X 10m9 A/cm2 were obtained with K' as the primary ion for the three types of membranes, respectively. Preliminary results indicate that the exchange current data obtained with this technique are complementary to the potentiometric response observed for the membranes studied.
Journal of Electroanalytical Chemistry, 1999
Glassy carbon electrodes coated with the poly(estersulfonate) Kodak AQ55 were used in acetonitrile solutions of various supporting electrolytes to study the ion-exchange voltammetric behaviour of some electroactive cations, namely the monocharged cation (ferrocenylmethyl)trimethylammonium (FA + ) and the dications Ru(bpy) 3 2 + (bpy= 2,2%-bipyridine), methylviologen, butylviologen and heptylviologen. For all the electroactive cations, it was found that the success in their ion-exchange is determined by the size of the supporting electrolyte cation. In particular, lowering the steric hindrance of the supporting electrolyte cation results in a more significant ion-exchange competition with the electroactive cation. As far as different redox analytes are concerned, it was observed that the preconcentration efficiency increases with increasing charge and for electroactive species with the same ionic charge, parallels the order of decreasing steric hindrance. In the case of the viologens, this last factor seems to overcome the hydrophobic one, where the small (but less hydrophobic) methylviologen is preconcentrated more efficiently than the large (but more hydrophobic) heptylviologen.
Electrochimica Acta, 2014
Specific features of voltammetric studies with modified electrodes are subject of the consideration performed in the review. Basing on the approaches developed in preceding works, three groups of problems are discussed. The first one concerns a regular treatment of quasi-equilibrium cyclic voltammograms of modified electrodes. It is emphasized that singular points of such curves and their form depend on the system parameters (charges of immobile charge carriers, binding of counter-ions with the film fragments). As regards the second group of problems, its existence results from possible effects of the film porosity on the rates of reduction/oxidation processes with participation of particles capable to react on the film/solution interface. The main conclusion followed from the performed discussion is in the possibility of appearing the limiting currents not controlled with tested particles diffusion within the adjacent electrolyte. In scope of the third group of problems, the tested particles reactions on the electrodes covered with metal-containing polymer films are considered. As follows from the proper analysis, the current-voltage curves of these processes are described with the well-known equations of the electrochemical kinetics. Validity of the obtained conclusions is illustrated with the corresponding experimental results.
Ion-Exchange Voltammetry at Polymer Film-Coated Nanoelectrode Ensembles
Analytical Chemistry, 1996
Ensembles of nanoscopic disk-shaped electrodes have been shown to offer enhancements in electroanalytical detection limits relative to electrodes of macroscopic dimensions (e.g., disk electrodes with diameters of ∼1 mm). Enhancements in electroanalytical detection limits have also been observed at macroscopic electrodes that have been coated with films of ion-exchange polymers. In this paper we combine these two concepts. We demonstrate that a nanoelectrode ensemble (NEE) that has been coated with a thin film of the Kodak ion-exchange polymer AQ 55 shows enhanced electroanalytical detection limits relative to the uncoated NEE and to the coated macroscopic electrode. To our knowledge, this is the first investigation of the electrochemistry, and the electroanalytical advantages, of polymer film-coated NEEs.
Electrochimica Acta, 2006
This paper describes the preparation and characterisation of a polymeric electrode coating based on a composite of the poly-(estersulphonated) Eastman AQ55 ® (AQ55) and poly-(3-methylthiophene) (PMeT), which is used for the controlled uptake and partial release of electroactive cations in acetonitrile solutions. The film is prepared by electrochemical oxidation in acetonitrile of 3-methylthiophene on glassy carbon disks or Pt-quartz crystal electrodes pre-coated with a thin film of AQ55. The electropolymerisation process is controlled so that the overall number of positive charges of oxidised PMeT is equal to the number of negative charges of the sulphonate groups of AQ55. Cyclic voltammetry and quartz crystal microbalance measurements indicate that the AQ55/PMeT mixed film is stable in acetonitrile and that its cation-exchange properties depend on the applied potential. When the PMeT moieties are reduced, the film incorporate cations; following electrochemical oxidation of the coating causes a release of the incorporated cations which, however, is only partial. Scanning electron microscopy (SEM) examination of cross sections of the composite polymer layer indicate that it is really a bi-layer, made by an inner compact layer of AQ55 on which a thicker and porous PMeT layer is grown. The outer PMeT layer acts as a barrier whose ionic charges can be changed electrochemically from positive (oxidation) to neutral (reduction). These ionic charges hinder or allow, respectively, the permeation of redox cations which tend to interact with the negatively charged sulphonic sites of the AQ55 layer. Direct self-neutralization of part of the positive charges of oxidized PMeT by the AQ55 sulphonic groups allows the release of part of the redox cations incorporated previously in the mixed film when PMeT is in the reduced state. By operating in acetonitrile solutions without added electrolyte it is possible to increase the fraction of redox cations which are released in consequence of the oxidation of PMeT; this suggests a slower and only partial oxidation of PMeT under such experimental conditions.
Talanta, 1997
Electrodes modified by the electrodepozition of conducting organic polymers such as poly(3-methylthiophene)(PMT), polypyrrole (PPY) and polyaniline (PAN) were used as chemical sensors for voltammetric analysis and flow injection detection of some organic and biological molecules. The electrochemical behaviors of catechol, ascorbic acid, hydroquinone, dopamine, epinephrine, acetaminophen and p-aminophenol were examined by differential pulse voltammetry. The electrochemical behavior of these molecules at different electrodes was compared and the effects on behavior of electrolyte type and its pH and the film thickness were systematically examined. The results showed that the proposed modified surface catalyzes the oxidation of these compounds. Electrocatalytic 'efficiency' decreases in order of poly-3-methylthiophene, polypyrrole and polyaniline. Voltammetric peak positions were affected by the nature of the electrolyte and its pH. Also, the effect of increasing film thickness was to observe increased peak heights. Polymer coated electrodes were also used in an amperometric detector for flow injection analysis of most of the these compounds. The responses of the polymer electrode were 5-15 times larger as compared with those of bare platinum. PMT showed improved performance as an amperometric detector for flow injection analysis systems over other types of polymer electrodes. Detection limits as low as 10-8-10 9 M were achieved using the PMT, compared with 10 -6 10 8 M using platinum electrodes. In the flow injection analysis, with increasing molecular weight of analyte molecules was to observe decreased peak heights. © 1997 Elsevier Science B.V.
Analytical Chemistry, 2006
The ion transfer across the water-solvent polymeric membrane interface is investigated by using a new device based on a modification of a commercial ion-selective electrode body that permits the accommodation of a platinum counter electrode inside the inner filling solution compartment and, therefore, use of a four-electrode potentiostat with ohmic drop compensation. This device is used here to apply two different double potential pulse techniquessdifferential pulse voltammetry and additive differential pulse voltammetryswhich are more advantageous than other voltammetric techniques, such as normal pulse voltammetry or cyclic voltammetry, for the determination of the characteristic electrochemical parameters of the system. This is due to the concurrence of two factors in these double potential pulse techniques, the peak-shaped response together with a considerable reduction of undesirable current contributions.
Development in Voltammetric Analysis with Chemically Modified Electrodes and Biosensors
2012
A research done in the field of chemically modified electrodes (CMEs) within the last years is reviewed (208 references). Results obtained in our laboratory are related to those reported by other authors. Main areas are the theory and application of CMEs to the trace metal determination and speciation, electrocatalysis and mediated biocatalysis, utilization of polymer films as well as molecular recognition by DNA.
Analytica Chimica Acta, 1993
Perfluonnated polycatlomc polymers (Tosflex) were appbed for preparmg polymer-modtied electrodes able to preconcentrate amomc complexes of Cu+ electrogenerated m situ at the electrode/polymer Interface by reducmg Cu*+ solutions m the presence of chlonde Ions The species Incorporated mto the polymenc coating, namely C&l;, was detected by a sultable lmear sweep voltammetnc reoxldatlon scan The dependence of the reoxldatlon peak current on experunental parameters such as amount of modtier, electrogeneratlon-preconcentratlon time and solution concentrations of Cu'+ and Cl-was studled The posslbd~ty of applymg Tosflex-moddied electrodes to copper speclatlon studies was also exammed In partrcular, the Influence on the ion-exchange voltammetic responses of some ammo aads such as hlstldme, glycme and glutanuc acid whsh, at the pH employed m this study, carry positive, neutral and negative lomc charges, respectively, IS discussed Some of the advantages and lmutatlons of Tosflex-modified electrodes compared with Nafion-coated electrodes and the hangmg mercury drop electrode are cntlcally evaluated