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  • Chemistry  (15)
  • Biochemistry and Biotechnology  (1)
  • Gold  (1)
  • 1
    Digitale Medien
    Digitale Medien
    A study of the anodic oxidation of thiophosphate at a gold electrode in 0.10 M sodium hydroxide by double-potential-step chronocoulometry in a thin-layer cell (1989)
    Weinheim : Wiley-Blackwell
    Electroanalysis 1 (1989), S. 125-131 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The oxidation of adsorbed SPO33- during the positive potential scan at a gold electrode is a major contributor to the total anodic signal that is catalyzed by formation of surface oxide. The number of electrons for oxidation of SPO33- in both the adsorbed (nads) and solution (nsoln) states was determined to be 6 equiv mol-1 on the basis of double-step chronocoulometry in a thin-layer cell. The products are concluded to be PO32- and SO43- on the basis of these n values, 31P NMR spectra, and a positive BaCl2 test for sulfate. The adsorption of SPO33- on Au is concluded to be consistent with the Langmuir isotherm to a coverage of θ = ca. 0.9, which is achieved for 0.6 mM Na3SPO3.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140010207
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  • 2
    Digitale Medien
    Digitale Medien
    Variation in PED response at a gold microelectrode as a function of waveform parameters when applied to alditols and carbohydrates separated by capillary electrophoresis (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 1015-1019 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Capillary electrophoresis ; Pulsed electrochemical detection ; Alditols ; Carbohydrates ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Results are presented from a systematic study of the noise (N) and peak-to-noise ratio (P/N) obtained for pulsed electrochemical detection (PED) at a gold micro-wire electrode applied to a mixture of alditols and monosaccharides separated by capillary electrophoresis (CE). The electrode potentials and time periods for oxidative cleaning and reductive reactivation of the electrode were held constant in the PED waveform at minimum allowable values and the time period for digital integration of electrode current (tint) was varied from 50 to 800 ms by 50-ms intervals. The value of N was virtually independent of tint and P/N increased approximately as a linear function of tint in the range 50-200 ms corresponding to waveform frequencies in the range 4.5-2.7 Hz. A detection limit of 9 fmol glucose was determined for a 4-nL injection using tint = 200 ms.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140071104
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  • 3
    Digitale Medien
    Digitale Medien
    Pulsed amperometric detection based on direct and indirect anodic reactions: A review (1989)
    Weinheim : Wiley-Blackwell
    Electroanalysis 1 (1989), S. 189-197 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Pulsed amperometric detection (PAD) is applicable for the quantitative detection of numerous organic compounds that adsorb at noble metal electrodes but cannot be detected satisfactorily by conventional amperometry at constant (dc) applied potential. A multistep waveform is applied in PAD with chrono-amperometric detection based on faradaic signals, which frequently are produced by surface-controlled reactions. We briefly review applications of PAD for liquid chromatography and present a unified explanation of the various modes of anodic response.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140010302
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  • 4
    Digitale Medien
    Digitale Medien
    The importance of adsorption in anodic surface-catalyzed oxygen-transfer reactions at gold electrodes (1990)
    Weinheim : Wiley-Blackwell
    Electroanalysis 2 (1990), S. 21-30 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A large number of anodic oxygen-transfer reactions were studied at Au electrodes in both acidic and alkaline media. Results of competitive adsorption studies are interpreted and support the conclusion that adsorption is a prerequisite to subsequent oxygen- and electron-transfer steps. Many of these oxidation reactions gave the voltammetric appearance of reversible waves, even though the observed half-wave potential values were shifted hundreds of millivolts positive of the thermodynamic potentials. A catalytic mechanism is proposed in which adsorbed hydroxyl radicals (AuOH) participate in the oxygen-transfer step. The absence of pH effects on half-wave potentials for several inorganic compounds suggests that the electron transfer precedes the deprotonation step for these reactants.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140020106
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  • 5
    Digitale Medien
    Digitale Medien
    A study of ethylamine at a gold rotating ring-disk electrode using pulsed electrochemical detection at the ring (1996)
    Weinheim : Wiley-Blackwell
    Electroanalysis 8 (1996), S. 726-731 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Ethylamine ; Gold ; Voltammetry ; Adsorption ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Linear scan (cyclic) voltammetry at the disk with simultaneous pulsed electrochemical detection (PED) at the ring of a rotated ring-disk electrode (RRDE) is demonstrated to be applicable for studies of the complex anodic behavior of ethylamine at gold electrodes in 0.10 M NaOH. The oxidation of ethylamine at the disk occurs during positive scans concomitantly with formation of surface oxide (Au → AuOH → AuO). However, the final oxide-covered surface (AuO) is inert for further ethylamine oxidation. Data obtained at the RRDE demonstrate that the total ethylamine signal at the disk is composed of simultaneous contributions from: oxidative desorption of ethylamine preadsorbed at the oxide-free Au surface and oxidation of ethylamine transported to the disk simultaneously with oxide formation. Based on ring-disk data, preadsorbed ethylamine is estimated to correspond to a fractional surface coverage of 0.7 ± 0.1 monolayer for 10 to 60 μM ethylamine. Of this coverage, ca. 75% corresponds to ethylamine coadsorbed reversibly with OH- and 25% to ethylamine adsorbed irreversibly by a mechanism concluded to be chemisorption.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140080805
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  • 6
    Digitale Medien
    Digitale Medien
    Activated pulsed amperometric detection of cysteine at platinum electrodes in acidic media (1997)
    Weinheim : Wiley-Blackwell
    Electroanalysis 9 (1997), S. 1397-1402 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Pulsed amperometric detection ; Cysteine ; Platinum electrode ; Sulfhydryl compounds ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Anodic voltammetric detection of sulfhydryl compounds, represented here by cysteine, at Pt electrodes in acidic media occurs concomitantly with anodic generation of surface oxide. It is speculated that the adsorbed hydroxyl species (PtOH), proposed to be the intermediate product in formation of the inert oxide (PtO), is the source of O-atoms transferred to the sulfonic acid produced by oxidation of the sulfhydryl moiety. However, as a consequence of this electrocatalytic response mechanism, application of the traditional three-step waveform for pulsed amperometric detection (PAD) of sulfhydryl compounds is accompanied by a large background signal resulting from PtO formation. To diminish the background signal, the traditional three-step PAD waveform has been modified by insertion of a brief (100 ms) anodization step prior to the detection step to activate the Ptsurface by the generation of PtOH with minimal conversion to PtO. The subsequent negative step from the activation potential (Eact) to the detection detection potential (Edet 〈 Eact) permits the PtOH to be harvested within the detection mechanism without significant background signal.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140091805
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  • 7
    Digitale Medien
    Digitale Medien
    The coulometric determination of chemical oxygen demand (1997)
    Weinheim : Wiley-Blackwell
    Electroanalysis 9 (1997), S. 279-283 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Chemical oxygen demand ; Coulometry ; Chromium ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The chemical oxygen demand (COD) of solutions containing various organic compounds is calculated from the net faradaic charge (Qnet) estimated for the total electrolytic oxidation of CrIII generated during oxidative degradation of the organic compounds in acidic media containing excess CrVI. Values of Qnet for conversion of CrIII to CrVI are estimated from the linearized chronoamperometric data plotted as In {itat, t} vs. t. This procedure is preferred over determinations of Qnet from the total integrals of itot over the entire electrolysis period because of large errors that can result from uncertainty in the background current (ibkg) for t → ∞. The proposed coulometric procedure offers the benefit that reagent solutions can be reused, thereby minimizing the need for disposal of wastes containing toxic CrVI. This procedure was applied in a single digest solution for consecutive determinations of COD. Average COD values for potassium acid phthalate and glucose were 103.8% (s - 6.0, N - 10) and 100.2% (s - 4.2, N - 11), respectively, based on the theoretical degradation to CO2. In comparison for these same samples, an EPA approved method, based on colorimetric determination of CrIII, gave COD values of 101.4% (S - 1.4, N - 5) and 100.1% (s - 1.4, N - 5) of the theoretical. Statistical tests indicate no significant difference in the COD values determined for these compounds using the coulometric and EPA methods.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140090403
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  • 8
    Digitale Medien
    Digitale Medien
    Activation of titanium electrodes for voltammetric detection of oxygen and hydrogen peroxide in alkaline media (1997)
    Weinheim : Wiley-Blackwell
    Electroanalysis 9 (1997), S. 273-278 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Titanium ; Voltammetry ; Oxygen ; Hydrogen peroxide ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Bright, freshly-polished Ti electrodes give minimal cathodic response for O2 and H2O2 in 1.0 M NaOH. However, the response is increased gradually by repeated application of a triangular waveform within the approximate potential limits of O2 response (ca. -1.5 to -0.7 V vs. SCE). This same voltammetric pretreatment applied for excessive periods results in formation of golden films on the Ti surfaces that are active for reduction of O2 and H2O2. Levich plots of cathodic current for O2 and H2O2 at rotated golden-Ti disk electrodes in 1.0 M NaOH (-1.35 V) are linear over a large range of rotational velocity (42 to 513 rad s-1), a behavior considered to be indicative of fast heterogeneous kinetics. Ring-disk data demonstrate that a small amount of H2O2 is produced throughout the potential region for O2 reduction and H2O2 is concluded to be an intermediate product in the O2-reduction mechanism. These observations are consistent with those reported previously for single-crystal TiO2 electrodes.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140090402
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  • 9
    Digitale Medien
    Digitale Medien
    Pulsed electrochemical detection at noble metal electrodes in liquid chromatography (1992)
    Weinheim : Wiley-Blackwell
    Electroanalysis 4 (1992), S. 367-380 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Pulsed electrochemical detection ; aliphatic compounds ; liquid chromatography ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The direct electrochemical detection of numerous polar aliphatic compounds is achieved at Au and Pt electrodes under the control of multistep potential-time waveforms. In this technique, called “Pulsed Electrochemical Detection (PED),” the waveforms manage the sequential processes of sampling the faradaic signal, from the oxidation of analyte, followed by oxidative cleaning and reductive reactivation of the electrode surfaces. The response mechanisms in PED are strongly influenced by surface properties of the electrodes and, therefore, members of each chemical classification detected are observed to produce virtually identical voltammetric response. Consequently, applications of PED have their greatest analytical significance when coupled with Liquid Chromatography (LC) to achieve a priori resolution of complex mixtures. The basic concepts of PED are reviewed and LC-PED results are presented for a variety of samples containing mixtures of alcohols, carbohydrates, alkanolamines, amines, and sulfur compounds.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140040404
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  • 10
    Digitale Medien
    Digitale Medien
    Fast pulsed amperometric detection at noble metal electrodes: A study of oxide formation and dissolution kinetics at gold in 0.1 M NaOH (1992)
    Weinheim : Wiley-Blackwell
    Electroanalysis 4 (1992), S. 741-749 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Chronocoulometry ; pulsed amperometric detection ; gold oxide ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The anodic charge (qa) for oxide formation, obtained by potential-step chronocoulometry at a Au minidisk electrode, is nearly a linear function of log (t/ms) for t = ca. 3-30 ms with a slope proportional to the applied overpotential for oxide formation. It was demonstrated that, contrary to popular opinion based on voltammetric observation at slow scan rates (φ), the anodic current for oxide formation obtained using a linear potential-scan waveform is not a linear function of φ at large values of φ. It was also demonstrated that a reverse potential-step waveform can be used to interrupt the rapid oxide growth and, perhaps, inhibit the conversion of the hydrous oxide (AuOH) to the inert oxide (AuO). This result has probable significance for decreasing the background current during anodic pulsed amperometric detection of amines and sulfur compounds whose oxidation mechanisms are believed catalyzed by AuOH but not by AuO. The cathodic charge (qc) for oxide dissolution is approximately a linear function of t with a slope that is proportional to the applied potential.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140040802
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