Showing papers on "Polarography published in 1998"
TL;DR: In this article, the results of a study on the determination of trace levels of mercury in natural saltwaters using screen-printed carbon electrodes modified with Sumichelate Q10R, a chelating resin containing dithiocarbamate groups, which binds mercury strongly and selectively are reported.
Abstract: The results of a study on the determination of trace levels of mercury in natural saltwaters using screen-printed carbon electrodes modified with Sumichelate Q10R, a chelating resin containing dithiocarbamate groups, which binds mercury strongly and selectively are reported. Cyclic voltammetric measurements indicate that mercury(II) is preconcentrated by complexation at the modified electrode, giving peak currents which are about one order of magnitude higher than those obtained at an unmodifed screen-printed electrode. The voltammetric pattern is characterized by a broad reduction peak to which a sharp and well-resolved reoxidation peak is associated. Trace (subnanomolar) concentrations of mercury can be determined at the screen-printed modified electrode by adopting a complexation-anodic stripping procedure with detection via differential pulse voltammetry. The method is characterized by a low detection limit (3j blank/sensitivity) of 12 pM with 20 min complexation and 5 min reduction at ‐0.5 V. Excess copper interferes in the analysis of mercury only when present in more than hundred-fold excess. Data concerning the application of modified screen-printed electrodes to the analysis of mercury in water samples from the channels of Venice (Italy) are presented and discussed.
99 citations
TL;DR: In this article, the complexation between Zn 2+ and glutathione (GSH), in borate buffer, is studied by Differential Pulse Polarography (DPP) data obtained at pH 8.5 from a titration of Zn2+ by GSH, i.e. at different GSH-to-Zn 2+) concentration ratios have been analyzed by a recently proposed multivariate curve resolution method.
61 citations
TL;DR: In this article, a combination of field and laboratory studies involving several voltammetric techniques has shown that the observed signal is due to the reduction of both a solution species and a surface species which may be adsorbed from solution, or formed in situ at the mercury surface as HgS is reduced to liberate S(−II).
33 citations
TL;DR: In this article, the authors proposed a 2-nitroso-1-naphthol-4-sulfonic acid-tetradecyldimethylbenzylammonium ion-associated complexes which are quantitatively adsorbed on microcrystalline naphthalene in the pH ranges 5.7-11.0 and 8.0-10.5, respectively.
27 citations
TL;DR: A theoretical equation of the current vs. potential curve of amines at a dropping electrolyte electrode is derived in this article, where the partition processes of both protonated and neutral forms of amine at O/W interface are taken into account.
26 citations
TL;DR: In this article, the authors investigated the correlation between the surface morphology of glassy carbon electrodes modified with mercury and the characteristics of voltammograms of copper, lead, cadmium and mercury.
Abstract: This article deals with the investigation into the correlation between the surface morphology of the glassy carbon electrodes modified with mercury and the characteristics of voltammograms of copper, lead, cadmium and mercury. The methods of voltammetry and in-situ microscopy were used. It is shown that nucleation is the slow step of the mercury evolution on glassy carbon electrode. Overvoltage of the process is reduced after nuclei form. The factors, which determine the distribution of mercury on the electrode surface, are the degree of polishing of glassy carbon and exposure of the electrode to the air. Two types of insoluble compounds are formed on the electrode in solutions containing chloride-ions. One type of the compounds, a calomel, forms a reversible redox pair and is reduced to metallic mercury during cathodic polarization of the electrode. Well-defined voltammograms of the metals are observed in this case. The other type of the compounds appears during anodic polarization of the mercury-coated electrode in solutions containing chloride-ions when the mole ratio HCl/Hg2+ of the solution is less than 104. The formation of these compounds, which possess anomalous properties, is followed by appearance of a cathodic peak in the anodic voltammogram (‘reverse’ peak). A special electrochemical ‘conditioning’ of the electrode is needed to remove the precipitate of insoluble compounds. Otherwise, unusual ‘reverse’ peaks complicate the voltammograms of the elements to be determined.
25 citations
TL;DR: In this paper, the polarographic characteristics of metal-phytochelatin complexes (Me-PC) extracted from the marine alga Phaeodactylum tricornutum were investigated by the use of differential pulse polarography (DPP) at dropping mercury electrode (DME).
Abstract: The polarographic characteristics of metal-phytochelatin complexes (Me-PC) extracted from the marine alga Phaeodactylum tricornutum were investigated by the use of differential pulse polarography (DPP) at dropping mercury electrode (DME). Four metal-phytochelatin complexes differing for the metal bound, namely Cd-, Pb-, Zn- and Cu-PC, were studied, and their polarographic behavior was compared with that of Cd,Zn-thionein and Zn-thionein of mammalian origin. The polarographic characteristics of Me-PC exhibit a dependence on the metal bound to the peptides and on the pH of the solution. Both the organic and inorganic part of Me-PC are electroactive and give polarographic responses depending on their chemical form in solution. Dissociation and formation processes were investigated. The order of stability of the complexes was K′Cu−PC > K′Pb−PC ≥ K′Cd−PC > K′Zn−PC. The same electrochemical mechanisms were found to characterize both the polarographic behavior of metallothioneins and metal-phytochelatin complexes.
20 citations
TL;DR: In this paper, the electrochemical behavior of the herbicides benfluralin and trifluralin was studied using differential pulse polarography in universal buffers of pH range 2.0 to 12.0.
Abstract: The electrochemical behavior of the herbicides benfluralin and trifluralin was studied using differential pulse polarography in universal buffers of pH range 2.0 to 12.0. The cathodic peak observed for the herbicides are attributed to the reduction of nitro groups and showeu to be pH dependent. Differential pulse polarography at dropping mercury electrode was used to establish an electroanalytical procedure for the determination of the herbicides benfluralin and trifluralin in formulations, soils and grains. Quantitative measurements were successful in the concentration range of 1.25X10−5 to 2.8.5X10−9 M, the lower concentration representing the detection limit by differential pulse polarography.
15 citations
TL;DR: A highly sensitive polarographic method was developed for the determination of EDTA added as a preservative in certain pharmaceutical preparations and the results obtained were in agreement with those obtained by a reference method.
14 citations
TL;DR: In this article, the development of renewed miniaturized mercury multi-purpose (multi-mode) electrodes as an inseparable part of modern polarography and voltammetry; casette-type, pen-type and PC-controlled systems, including the polarographic/voltammetric set.
Abstract: Information is given about the development of renewed miniaturized mercury multi-purpose (multi-mode) electrodes as an inseparable part of the development of modern polarography and voltammetry; casette-type, pen-type and PC-controlled systems, incl. the polarographic/voltammetric set. According to the experimental behavior and ranges of their radii the regimes of renewed stationary mercury electrodes are divided into three categories – mini-, semimicro- and microelectrodes (mE, sμE and μE). Their spontaneously growing, stepwisely growing, stationary and contracting (compression) modes are schematically outlined. Information on basic functional properties of the discussed renewed mercury semimicro- or microelectrodes using meniscus and microdrop-electrodes, by means of the d. c., anodic stripping and adsorptive stripping voltammetry is given.
14 citations
TL;DR: A simple method for the determination of the urinary tract antibiotic nifuroxazide has been developed in this paper, where electrochemical reduction of the nitro group at mercury and carbon paste electrodes can be used for determination with and without adsorptive preconcentration.
Abstract: A simple method for the determination of the urinary tract antibiotic nifuroxazide has been developed. The electrochemical reduction of the nitro group at mercury and carbon paste electrodes can be used for the determination with and without adsorptive preconcentration. The influence of parameters like pH of the background electrolyte, preconcentration potential and preconcentration time on the sensitivity of the method has been studied. Modification of the carbon paste by addition of nonpolar polystyrene/divinylbenzene particles has been investigated to enhance the adsorption properties of the surface. Concentrations as low as 10 ng/mL could be determined in urine without interferences.
TL;DR: A novel approach for the determination of the stannous content in cold kits for labelling with 99mTc is described, based on differential pulse polarography on the hanging mercury drop electrode in a methanol/water/perchloric acid mixture.
TL;DR: In this article, a model was proposed for the voltammetric study of metal ions in mixtures of macromolecular and simple ligands, with the assumption that the complexes formed are totally labile or totally inert.
TL;DR: The ratio derivative polarography method has been successfully applied for resolving ternary mixtures of copper, cadmium and nickel, which have overlapped polarograms in pH 2.87 Britton-Robinson buffer.
TL;DR: In this article, the interaction of divalent metal ions with styrene-maleic acid-copolymer (SMA copolymer) has been studied and the results point to a strong influence of metal dissolution on the mechanism of deposition of MA copolymers on copper, zinc and nickel electrodes.
TL;DR: In this article, a two-step reduction of Zn(II) ions at the dropping mercury electrode in 1 M NaClO 4 /0.001 M HClO4 was examined in wide potential and frequency ranges, using the impedance method.
Abstract: A two-step reduction of Zn(II) ions at the dropping mercury electrode in 1 M NaClO 4 /0.001 M HClO 4 in the presence of N , N' -dialkylthioureas was examined in wide potential and frequency ranges, using the impedance method. The rate constant of the first electron transfer increases with increasing concentration of N , N' -dialkylthioureas, whereas that of the second electron transfer depends largely on the double layer effects, particularly, on the orientation of molecules on the electrode surface.
TL;DR: In this article, a semi-empirical hydrodynamic model for stripping voltammetric measurements carried out in macromolecular and simple ligands is presented. But the model assumes excess of ligand and absence of both electrodic adsorption and kinetic effects.
Abstract: A model, originally developed for polarography of metal ions in mixtures of macromolecular and simple ligands, is extended to stripping voltammetric measurements carried out in such systems. Among other hypotheses, the model assumes excess of ligand and absence of both electrodic adsorption and kinetic effects (complexes are supposed to be totally labile or totally inert). The different hydrodynamic conditions in stripping voltammetry in respect to polarography make it necessary to modify some equations of the original model. The reliability of this semiempirical approach is tested by studying the ZnII + polymethacrylic acid + phthalate system, which is a typical system with labile complexation, The mean values of the formation constant and diffusion coefficient ratio obtained by this approach are quite similar to those determined from polarographic experiments. The introduction of a semiempirical hydrodynamic parameter p, analogous to that previously used in the model for a unique macromolecular complex, yields satisfactory results.
TL;DR: In this paper, the electrochemical behavior of the herbicide prometryne was studied in aqueous solutions by DC polarography, differential pulse and cyclic voltammetry and by constant potential coulometry.
Abstract: The electrochemical behavior of the herbicide prometryne was studied in aqueous solutions by DC polarography, differential pulse and cyclic voltammetry and by constant potential coulometry. Only the protonated form of prometryne can be reduced at pH < 6.5. The electrode process includes two irreversible steps. The two-electron reduction of the C–S bond leads to its splitting and a release of methylthiol molecule. The triazine ring of the reduction product is immediately reduced under the uptake of two electrons. Both the intermediate and final products of constant potential electrolysis were identified using chromatographic techniques and mass spectrometric analysis. The reduction mechanism of other 2-methylthio-4,6-dialkylamino-s-triazines is identical.
TL;DR: A procedure in which fluorine in the air was preconcentrated in a chromatomembrane cell and its content was determined by adsorptive polarography, which yields a sensitive oscillopolarographic wave at -0.67 V.
TL;DR: In this paper, the polarographic and voltammetric behavior of N,N-dimethyl-4-amino-2′-carboxyazobenzene was investigated and optimum conditions have been found for its determination by tast polarography in the concentration range of 2-100 μmol 1−1.
Abstract: The polarographic and voltammetric behaviour of N,N-dimethyl-4-amino-2′-carboxyazobenzene was investigated and optimum conditions have been found for its determination by tast polarography in the concentration range of 2-100 μmol 1−1, differential pulse polarography at a dropping mercury electrode in the concentration range of 0.2-100 μmol 1−1, differential pulse voltammetry at a hanging mercury drop electrode in the concentration range of 0.02-10 μmol 1−1 and adsorptive stripping voltammetry in the concentration range of 0.2-100 nmol 1−1.
TL;DR: In this article, the catalytic polarographic nickel prewave was investigated by making appropriate correlations between prewave current and complex species concentrations as calculated by means of available formation constants, and it was concluded that the active species is (D-penicillaminato-N, S )nickel(II) [NiL], whereas the bis-ligand complex, [ NiL 2 ] 2-, is inert and does not play any role in the electrode process.
Abstract: The catalytic polarographic nickel prewave was investigated by making appropriate correlations between prewave current and complex species concentrations as calculated by means of available formation constants. It was concluded that the active species is (D-penicillaminato- N , S )nickel(II) [NiL], whereas the bis-ligand complex, [NiL 2 ] 2- , is inert and does not play any role in the electrode process. The catalytic character of the electrode process originates from the regeneration of [NiL] by the reaction of adsorbed ligand molecules with free nickel ions available in the bulk of the solution. Conversely, all the complex species in the Ni 2+ -cysteine system are labile. Consequently, the reaction mechanism in this case may include the dissociation of the complex [NiL 2 ] 2- as an alternative path for the generation of the active species, [NiL]. The bell-shaped form of the prewave was interpreted in terms of potential-dependent catalyst adsorption.
TL;DR: In this paper, phase-sensitive alternating current polarography was used to investigate the adsorption of insulin and soybean trypsin inhibitor (STI) on the mercury electrode.
TL;DR: In this article, three selected electrodes were evaluated for the anodic stripping voltammetric (ASV) determination of Tl, Cd, Pb, Cu and for the quantification of Ni dimethylglyoxime by AdSV.
Abstract: In this study, three selected electrodes were evaluated for the anodic stripping voltammetric (ASV) determination of Tl, Cd, Pb, Cu and for the quantification of Ni dimethylglyoxime by adsorptive stripping voltammetry (AdSV). The measurements were performed by plating a mercury film on a RAM-microarray electrode, on an epoxy impregnated carbon electrode (ultratrace electrode) and on a conventional glassy carbon macroelectrode. The RAM electrode requires less Hg to perform a sensitive determination of the analytes. Caused by spherical diffusion effects, large current signals were obtained with this electrode without stirring the solution during the deposition step. By the use of the ‘ultratrace electrode’ a sensitive determination of Ni was possible without preplating a mercury film. Detection limits between 0.49 ppb and 2.42 ppb due to each analyte could be realized with the working electrodes examined.
TL;DR: In this article, the irreversible nature of the UO22+ transfer observed in the polarogram resulted from such slow processes involved in the ion transfer reaction as the adsorption/desorption of bis(diphenylphosphoryl)methane (BDPPM), and that the transfer reaction had irreversible characteristics.
Abstract: The ion transfer of UO22+ ion across an aqueous(w)/nitrobenzene(NB) interface was investigated by ion-transfer polarography using an aqueous electrolyte dropping electrode. It was found that the transfer of UO22+ from w to NB was facilitated by bis(diphenylphosphoryl)methane (BDPPM), and that the transfer reaction had irreversible characteristics. A potential generated at the UO22+ ion-selective electrode, which was prepared while referring to ion transfer data, revealed a reversible Nernstian response against the concentration of the UO22+ ion in an aqueous sample solution. The irreversible nature of the UO22+ transfer observed in the polarogram resulted from such slow processes involved in the ion transfer reaction as the adsorption/desorption of BDPPM or the UO22+-BDPPM complex at the w/NB interface. The feasibility of the electrolytic separation of uranium from neptunium and plutonium on the basis of a selective ion-transfer reaction is discussed.
TL;DR: In this paper, a convenient and accurate analytical procedure was developed for the trace determination of tetramethylthiuram disulphide in commercial fungicides and rubber accelerators for the purpose of quality control.
Abstract: A convenient and accurate analytical procedure has been developed for the trace determination of tetramethylthiuram disulphide in commercial fungicides and rubber accelerators for the purpose of quality control. Thiuram disulphide gives a well defined, diffusion controlled cathodic wave in 0.01 m pyridinium perchlorate in dimethylformamide with half-wave potential -0.36 V against a saturated calomel electrode. Determination has been made by normal pulse and differential pulse polarography using linear calibration plots.
TL;DR: In this paper, the mechanism of the electroreduction of Zn(II) at the dropping Hg electrode, inhibited by adsorbed triphenylphosphine oxide, was studied in solutions of pure acetonitrile and propylene carbonate.
TL;DR: In this article, the electrochemical behavior of dioxygen in the presence of adenine in dimethylformamide solution on the Hg electrode is studied, and evidence for the activation of O 2 is given by the shift of 150 mV towards more positive values of the one-electron reduction, accompanied by the autooxidation of adnine, while the adsorption of o 2 is shown by the characteristics of a polarographic pre-wave and voltammetric peak.
Journal Article•
TL;DR: In this paper, the general solution for all modes of double-pulse voltammetry for an electrode process under Nernstian behaviour coupled with a following fast chemical reaction (EC mechanism) has been derived.
Journal Article•