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  • 1
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A comparison was made of methods for measuring the copper complexation capacity of natural and synthetic organic ligands in freshwaters. Complexation capacity values close to theoretical were obtained for nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid, when the following separation or analysis methods were used to detect ionic copper: algal assay (Chlorella pyrenoidosa), an aluminum hydroxide resin, ion-selective electrode (ISE), and anodic stripping voltammetry (ASV) at the mercury film electrode (MFE) and Nafion-coated MFEs. No complexation capacity could be measured for Cu-NTA when the hanging mercury drop electrode (HMDE) was used.Results from the ISE and a resin with adsorbed aluminum hydroxide agreed closely with algal assay for the copper complexation capacity of solutions of fulvic acid and Fe-humic colloids. Analysis by ASV at the HMDE, MFE, and Nafion-coated MFE gave values-of more than an order of magnitude lower than the other techniques because these methods failed to detect the end point for partially labile complexes with a large complexation capacity. On the other hand, the use of differential pulse polarography (DPP) detected these labile copper complexes and yielded results comparable with those for algal assay. Comparable copper complexation capacities for pristine river water samples were obtained by algal assay (2.5-4.1 × 10-6 M Cu) and DPP (2.0-3.7 × 10-6 M Cu), with lower values for the aluminum hydroxide resin (0.8-1.1 × 10-6 M Cu). Because the ASV techniques gave much lower results (0.1-0.4 × 10-6 M Cu), they are clearly unsuitable for the determination of the complexation capacity of freshwaters.
    Additional Material: 3 Ill.
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  • 2
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cathodic stripping experiments of thioacetamide in alkaline solutions, pH = 13, were performed using a rotating silver disk electrode and a silver microelectrode. Applicability of these two electrode systems for the determination of thioacetamide over a wide range of concentrations has been found using the stripping peak of bulk silver sulfide. A further improvement in the detection limit is suggested when only an underpotential deposition layer of silver sulfide is formed during deposition. Then cathodic stripping analysis of thioacetamide below 10-8. M is feasible. The mechanism for the reactions during the deposition and cathodic stripping of thioacetamide in alkaline media at silver electrode has been elucidated.
    Additional Material: 13 Ill.
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  • 3
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The microvoltammetry and spectroelectrochemistry of (TPP)Co (where TPP is the dianion of tetraphenylporphyrin) are reported in toluene and benzene solutions, and provide the first examples of spectroelectrochemistry in these two low dielectric constant solvents. (TPP)Co undergoes four reversible oxidation-reduction reactions in toluene or benzene. The reductions involve one-electron transfers and occur at E1/2 = -0.86 and -2.03 V vs. SCE in both solvents. The oxidations involve the successive reversible abstraction of two electrons and one electron from the initial (TPP)Co species and occur at E1/2 = 1.00 and 1.27 V vs. SCE in both solvents. Each electrode reaction was spectrally and electrochemically characterized in toluene and benzene, and the data in these two solvents are compared to data obtained in CH2Cl2 where (TPP)Co redox reaçtions have been extensively characterized in detail. Special emphasis is placed on comparing the thin-layer spectra of [(TPP)Co1] in toluene and benzene with that in other solvents commonly used for nonaqueous electrochemical studies.
    Additional Material: 3 Ill.
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  • 4
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 7 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Electroanalysis 1 (1989) 
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 7 Ill.
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  • 7
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduced nicotinamide adenine dinucleotide (NADH) has been determined at submicromolar levels (the detection limit was 0.05 μmol/L) by using graphitized and glassy carbon electrodes obtained from different sources. Preliminary studies compared the sensitivity, stability, and reproducibility of such sensors during NADH measurements in linear-sweep voltammetry as well as at constant applied potential. High purity graphite carbon from Ringsdorff has been found to be the most suitable for NADH oxidation. To regenerate the electrodes after each voltammetric scan, washing with a large volume of distilled water under stirring conditions is required. When the sensitivity of the electrode decreases drastically, the sensor surface must be ground and polished with alumina. The nature of the carbon surface has a pronounced effect on the NADH response.
    Additional Material: 8 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Electroanalysis 1 (1989), S. 375-375 
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Electroanalysis 1 (1989) 
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemically modified carbon paste electrodes containing incorporated cobalt phthalocyanine (CoPC) were shown to exhibit an electrocatalytic response for the oxidation of carbohydrate derivatives from the alditol and aldonic, uronic, and aldaric acid families. The electrocatalysis, which is similar to that previously seen for simple carbohydrates, resulted in the electrolysis of these compounds between +0.4 and +0.6 V vs. Ag/AgCl where Co(II)PC is oxidized to Co(III)PC. The response was greatest for the alditols and decreased from the aldonic to the aldaric acids. When used to quantify these compounds following anion exchange chromatography, detection limits at +0.42 V ranged from 10 pmol for the alditols to the nanomole level for some of the aldaric acids.
    Additional Material: 6 Ill.
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