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  • 1
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1618-2650
    Keywords: Best. von Isoniazid, Oxalyldihydrazid, Hydrochinon, Resorcin, organ. Verbindungen ; coulometrische Titration ; Silber(II)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary Conditions are described for the efficient generation of silver(II) and the titration of organic compounds by electrogenerated silver(II). An electrolyte of 0.1 M silver nitrate and 5 M nitric acid at −10°C is used, with a gold generating anode and a current density of 1.5–5 mA/cm2. A potentiometric (platinum-S.C.E. pair) or biamperometric (platinum electrodes, 200 mV) end point detection is used. For potentiometric detection, the platinum electrode is preconditioned with AgO in nitric or by anodization. The compounds isoniazid, oxalyldihydrazide, hydroquinone, and resorcinol were titrated down to sub-milligram quantities with errors of 1–2%.
    Notes: Zusammenfassung Der verwendete Elektrolyt besteht aus 0,1 M Silbernitrat in 5 M Salpetersäure bei −10°C. Die Generatoranode besteht aus Gold (Stromdichte 1,5–5 mA/cm2). Die Bestimmung des Endpunkts erfolgt potentiometrisch (Pt/SKE) oder biamperometrisch (Pt-Elektroden, 200 mV). Für die potentiometrische Bestimmung wird die Indicatorelektrode mit einer Lösung von AgO in Salpetersäure oder durch elektrochemische Anodisierung vorbehandelt. Folgende Substanzen wurden bis herab in den sub-Milligramm-Bereich mit Fehlern von 1–2% titriert: Isoniazid, Oxalyldihydrazid, Hydrochinon, Resorcin.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1618-2650
    Keywords: Analyse von 1,2-Naphthochinon-4-sulfonat, 1,2-Naphthochinonsemicarbazon ; Polarographie, Voltammetrie ; elektrochem. Eigenschaften
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary A study of the electrochemical characteristics of 1,2-naphthoquinone-4-sulphonate, sodium salt, and of the semicarbazone of 1,2-naphthoquinone (Naftazone) was carried out using d.c., a.c. and d.p. polarography and cyclic voltammetry. Changes in the waves as a function of concentration and pH indicate evidence of adsorption phenomena at the potential of the reduction wave. These techniques also indicate the formation of a mercury derivative in the case of Naftazone. The quantitative determination of these two compounds is possible by polarography. Limits of detection are 5×10−6 and 5×10−8 M, respectively.
    Notes: Zusammenfassung Die elektrochemischen Eigenschaften von 1,2-Naphthochinon-4-sulfonat und -semicarbazon (Naftazon) wurden mit Hilfe der Gleichstrom-, Wechselstrom und Differentialpuls-Polarographie sowie der cyclischen Voltammetrie untersucht. Veränderungen an den Stufen in Abhängigkeit von Konzentration und pH-Wert deuten auf Adsorptionsvorgänge beim Potential der Reduktionsstufe hin. Im Falle von Naftazon wurde die Bildung eines Quecksilberderivats nachgewiesen. Beide Substanzen können polarographisch mit Nachweisgrenzen von 5×10−6 bzw. 5 × 10−8 M bestimmt werden.
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  • 4
    ISSN: 1618-2650
    Keywords: Eigenschaften von 2-Formylpyridin-thiosemicarbazon ; Polarographic ; Gleichstrom, Wechselstrom, Diff. puls, cycl. voltamm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary The electrochemical characteristics of 2-formylpyridine thiosemicarbazone (2-FPTS) have been studied by direct current, alternating current, and differential pulse polarography and cyclic voltammetry at a mercury electrode. This new cytostatic agent is reduced in a two-electron irreversible step at the nitrogen double bond of the side chain, in the pH range 0.2–12. A double anodic wave very close to the oxidation wave of mercury, corresponding to the formation of an organo-mercury compound, develops in neutral and alkaline media. These different electrochemical reactions are complicated by adsorption. In alkaline media, the carbon-nitrogen double bond reduction current decreases progressively with increasing pH due to formation of an electrochemically inactive species. Finally, a catalytic reduction wave of protons is developed in neutral solutions. Quantitative determination of the compound was possible in the range 1×10−7 to 1×10−3 M, using the diffusion controlled reduction wave at pH 7. The qualitative detection limit is 2×10−8 M (4 ng/ml).
    Notes: Zusammenfassung Die elektrochemischen Eigenschaften von 2-Formylpyridin-thiosemicarbazon wurden mit Hilfe der Gleichstrom-, Wechselstrom- und Differentialpuls-Polarographie sowie der cyclischen Voltammetrie an der Hg-Elektrode untersucht. Die neue cytostatische Substanz wird in einer irreversiblen Zweielektronen-Stufe an der Stickstoff-Kohlenstoff-Doppelbindung der Seitenkette reduziert (pH-Bereich 0,212). In neutralen und alkalischem Medium entwickelt sich eine anodische Doppelstufe dicht bei der Oxidationsstufe des Quecksilbers, entsprechend der Bildung einer quecksilberorganischen Verbindung. Diese elektrochemischen Reaktionen werden durch Adsorptionsvorgange verkompliziert. In alkalischem Medium nimmt der Reduktionsstrom der Kohlenstoff-Stickstoff-Doppelbindung mit zunehmendem pH ab, was der Bildung einer elektrochemisch inaktiven Substanz zugeschrieben wird. In neutraler Lösung wird eine katalytische protonische Reduktionsstufe gebildet. Die quantitative Bestimmung war im Bereich von 1·10−7 bis 1·10−3 M möglich, wobei die diffusionskontrollierte Reduktionsstufe bei pH 7 benutzt wurde. Die qualitative Nachweisgrenze liegt bei 2·10−8 M (4 ng/ml).
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  • 5
    ISSN: 1436-5073
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Spurenmengen von Naphthochinonen und von Methylenblau lassen sich mit Titan(III) titrieren. Dieses wird auf elektrochemischem Weg an einer Platinkathode aus 0,4-m Titantetrachlorid und 8-m Schwefelsäure gewonnen. Die Endpunktanzeige erfolgt potentiometrisch. Bei der Bestimmung von Naphthochinonen setzt man 15–50% Methanol zu, um die Adsorption von Naphthohydrochinon an der Generatorelektrode zu vermeiden. Für die Bestimmung von Methylenblau verwendet man 2 · 10−6-m Selen(IV)lösung als Katalysator und titriert bei 70° C, um die Reaktion zu beschleunigen.
    Notes: Summary Trace quantities of naphthoquinones and Methylene Blue are titrated with titanium (III) electrogenerated at a platinum cathode from an electrolyte of 0.4M titanium tetrachloride and 8M sulphuric acid, with potentiometric detection of the end-point. For naphthoquinones, 15–50% of methanol is added to prevent adsorption of the naphthohydroquinone product onto the generating electrode. For Methylene Blue, 2×10−6 M selenium(IV) is added as a catalyst and the titration is performed at 70° C to speed up the titration reaction.
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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: The voltammetric behavior of the hydrolyzed platinum(II) antitumor drug spiroplatin has been investigated at carbon paste and platinized platinum electrodes. The compound is oxidized to the corresponding platinum(IV) species at positive potentials near the solvent oxidation potential. On reversal of the potential scan, two 2-electron reduction steps occur on the carbon paste electrode, resulting in formation of platinum metal, as confirmed by scanning electron microscopy. In the presence of chloride, different reduction peaks associated with the formation of chloro structures are observed. These depend on the chloride ion concentration. The oxidation-reduction steps become more reversible at the platinum electrode. The nature of the oxidized species and the amount of platinum deposit were found to be related to the concentration of free chloride ions. Because the carbon paste electrode has the ability to differentiate the different oxidized forms upon reduction, its use is recommended for studying these compounds.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Four 15-membered ring cyclic compounds with two oxygen and two nitrogen atoms incorporated in the ring were prepared and evaluated as neutral carriers in lithium ion-selective electrodes. These ionophores, along with potassium tetrakis (p-chlorophenyl)borate and o-nitrophenyloctyl ether (NPOE), were included in the PVC matrix that coated the tip of a silver-wire electrode. The potentiometric selectivities of the electrodes towards lithium over sodium, potassium, calcium and magnesium were determined. Selectivity coefficients, K Li, Na pot ., as low as 9.5×10−3 were obtained and smaller coefficients for other metals, K Li, M pot ., were found. A calibration curve for lithium in the presence of 140 mmol/l sodium, with a linear portion having a slope of 51 mV/decade, was obtained. The effect of incorporating 1% trioctylphosphine oxide (TOPO) in the electrodes was studied. Comparison with the results obtained with 15-crown-4-ethers is made.
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  • 8
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Seven compounds of a new class of ionophores, acyclic formazanes, were synthesized and tested for the potentiometric selectivity for lithium ion, in polyvinyl chloride (PVC) membrane electrodes. Four different plasticizers were studied: o-nitrophenyloctyl ether (NPOE), o nitrophenylphenyl ether (NPPE), o-nitrophenylbutyl ether (NPBE), and o-nitrophenylbenzyl ether (NPBnE), as was the addition of trioctylphosphine oxide (TOPO). The ionophore, 1, 5-bis-(o-butoxyphenyl)-3-cyanoformazane (IIB) exhibited sodium-lithium selectivity, KpotLi, Na, of 6.2 × 10-3 by the matched potential method in the presence of 1% TOPO using NPPE plasticizer. The presence of TOPO generally causes a substantial increase in the lithium selectivity. Selectivities with respect to the lithium ion are reported for sodium, potassium, ammonium, barium, and calcium ions.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical characteristics of loprazolam mesilate have been evaluated in an aqueous solution using dc, ac, and normal and inverse pulse polarography, as well as cyclic voltammetry and controlled-potential coulometry. This drug undergoes three different reduction steps. The first, a four-electron transfer, corresponds to the reduction of the nitro group to give the corresponding hydroxylamine. The second, a two-electron transfer, corresponds to the reduction of the azomethine group, either before or after (in an acidic solution) hydrolysis. The third wave corresponds to a four-electron transfer in an acidic medium and to a two-electron transfer in an alkaline medium. In an acidic solution, this third step involves the two-electron reduction of the hydroxylamine group to the corresponding amine plus the two-electron reduction of the double bond between N-methylpiperazine and the imidazol group. In an alkaline solution, only the latter reduction takes place. Such behavior holds promise for analytical measurements of the drug.
    Additional Material: 7 Ill.
    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: The electrochemical behavior of Tizanidine has been studied using dc, ac, and pulse polarographic techniques. Reduction of the compound occurs through an electrochemical mechanism involving a six-electron transfer. Autoinhibition of the process resulting from the adsorption of species affects the reduction rate constants. At the electrode surface, adsorption proceeds through a competition between the oxidized and reduced forms.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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