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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 9189-9193 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 349 (1994), S. 582-596 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Electrochemical experiments in combination with infrared spectroscopy and subsurface concentration profiling yielded information on ionic processes at the membrane surface of glass electrodes and resulted in a detailed mechanism of the glass electrode response. This “dissociation mechanism” is based on phase boundary equilibria between anionic groups at the glass surface and hydrogen or alkali ions in the solution, which control the potential of the glass and the concentrations of ions attached to the surface groups. The resulting concentration gradients between glass surface and bulk glass cause an interdiffusion of the different ions, if they are not hindered sterically to penetrate into the glass, and a diffusion potential beneath the glass surface. The interdiffusion determines the course of the glass corrosion, which thus depends on whether protons or alkali ions are attached to the surface and interdiffuse with the alkali ions of the glass, leading, respectively, to a steady-state leached layer or a continuously growing alkali-exchanged layer. pH electrodes with La2O3-containing membrane glasses show delayed interfering potential drifts in neutral and alkali phosphate and fluoride solutions caused by LaPO4 and LaF3 deposits, respectively, at the membrane surface (“phosphate” and “fluoride errors”). Equations for the phase boundary potential and phase boundary concentrations are derived on a thermodynamic and kinetic basis and are verified experimentally. Glass leaching and alkali ion interdiffusion are studied, and the diffusion potential within a leached layer is determined. The formation periods of pH and of pM glass electrodes are explained, and an indirect part of the sodium error and an irreversible sodium error are detected. Leached and alkali-exchanged layers consist of modified glass and are not “gel” layers as generally assumed. Large exchange current densities of the phase boundary equilibria explain the stability of glass electrode potentials. Migration experiments with subsequent concentration profiling showed that glasses can be alkali ion, proton, and mixed alkali ion-proton conductors and yielded concentration-dependent mobilities of lithium ions and replacing protons in a lithium silicate glass. The unchanged pH response of membranes before and after field-driven protonation, in alkali-free solutions, excludes the exchange of different ions as the origin of the glass electrode response, as assumed by the ion exchange theory, and verifies the dissociation mechanism.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 349 (1994), S. 639-642 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract pH Measurements were carried out by means of cells containing Pt/hydrogen and glass electrodes, both equipped with the same type of ground glass sleeve junction carefully selected with respect to the leak rate. The cells were calibrated with the same set of standard buffers using multiple point calibration with linear regression. The slopes of the regression lines were compared with the theoretical (Nernst) slope of the E versus pH function and yielded the electromotive efficiency of the two cells. The accuracy of the measurements was obtained from the residual liquid junction potential errors.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 349 (1994), S. 603-606 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The determination of pH values suffers from two sources of error. One is the method of calibration of glass electrode cells. Multiple point calibration with linear regression is highly recommended instead of the usual bracketing procedure in cases where a precision of Δ pH〈±0.02 is required. Advantages of this method are discussed, particularly regarding the contribution of the liquid junction potentials to the cell emf. The second uncertainty is caused by batch to batch variations of Standard Reference Materials and their respective standard pH(S), actual values of which are part of the data set of microprocessor-controlled pH meters. Differential potentiometry is proposed as the method of choice to avoid these differences. It results in pH(S) independent of a particular material. Experimental data of the restandardization of pH reference materials are also presented.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 22 (1991), S. 128-136 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Nach einem systematischen Überblick über die verschiedenen, bei höheren Temperaturen und Drücken einsetzbaren Bezugselektrodenarten und die Möglichkeiten und Unsicherheiten ihrer Verbindung mit der Meßlösung wird ein einfaches in der Praxis bewährtes, isobares, nicht isothermes System beschrieben, bei dem durch kontrollierte Temperaturprofile Instabilitäten von Thermodiffusionspotentialen sicher ausgeschaltet sind.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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