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  • Chemistry  (3)
  • 1
    ISSN: 0951-4198
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: High-performance liquid chromatography in combination with mass spectrometric detection (atmospheric-pressure chemical ionization, APCI) was used to determine various isoflavones. Negative-ion APCI ionization has proved to be a suitable technique for determining this class of natural compound, as it provides quality mass spectra which give not only the molecular weight of the isoflavones, but also their molecular structures; consistent collision-induced dissociation pathways were elucidated and fragments are reported. Deuterium oxide was used to induce peak shifts in the mass spectra in order to determine the number of exchangeable hydrogen atoms in each molecule.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 2
    ISSN: 0951-4198
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: This paper reports a new thermal programmed desorption-mass spectrometry (TPD-MS) method for determining the number and relative strength distribution of basic sites in solid catalysts using CO2 as titrant. The overall desorbed CO2 area is proportional to the total basicity, while the number of peaks and their maximum temperature (Tmax) are related to the particular type of basic site and its strength. The activation energy for CO2 desorption from various basic sites in each catalyst was calculated via TPD-MS experiments conducted at a variable heating rate for each catalyst, using the Kissinger equation. Diffuse reflectance infrared analysis of the bands at 2000-1000 cm-1 for CO2 adsorbed on various catalysts allows one to elucidate the nature of the chemical species involved, which depends on the particular type of site. The total basicity results obtained are compared with those provided by an existing spectrophotometric method using benzoic acid (pKa=4.19) as titrant.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 3
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 8 (1994), S. 599-602 
    ISSN: 0951-4198
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: This paper reports a temperature-programmed desorption mass spectrometry method for determining the nature, number and distribution, according to relative strength, of acid sites in solid catalysts. By using pyridine as the titrant, the overall, Brönsted (B) and Lewis (L) acidities are determined. The Brönsted acidity is obtained individually by titration with 2,6-dimethylpyridine, whereas the Lewis acidity is calculated by difference. The desorption temperatures for the amines are used as measures of the relative strengths of the different types of acid sites. The results obtained are compared with those provided by a UV-visible spectrophotometric method reported elsewhere (J. M. Campelo et al., Can. J. Chem. Vol. 61, p. 544 (1983)).
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
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