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  • 1
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: BET-Surface Area measurments and Electron Microscopic investigations were carried out on a set of Pt—C catalysts previously heated in a limited supply of air, at temperatures between 50° and 1000°C.The alterations of the BET-Surface Areas as well as the changes occuring in the morphologic structure of the catalysts, after heating, were shown to be in agreement with the previously reported Electron Spin Resonance and Electrical Resisitivity measurements. The role of the oxygene is emphasized. Electron Micrographs are reproduced.
    Notes: Es wurden BET-Oberflächenmessungen und elektronenmikroskopische Untersuchungen an Pt—C-Katalysatoren durchgeführt, die in einem begrenzten Luftstrom auf Temperaturen zwischen 50° und 1000°C erhitzt wurden. Die Veränderung der BET-Oberfläche mit der Erhitzungstemperatur und die morphologischen Änderungen stehen in Übereinstimmung mit den früher berichteten Untersuchungen über die Struktureigenschaften dieser Systeme. Die Rolle des Sauerstoffs wird besonders hervorgehoben, es werden elektronenmikroskopische Aufnahmen gezeigt, die die morphologische Veränderung von Pt—C-Systemen nach thermischer Behandlung veranschaulichen.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Electron Spin Resonance and electrical resistivity measurements were carried out on Platinum-Coal catalysts previously heated at several temperatures between 50° bis 1000°C.The variation of the parameters of the ESR lines as well as this the resistivity with increasing temperature is shown to add further support to the hypothesis of „pseudosandwich“ complexes of Platinum with coal where an unpaired electron should be provided by platinum atoms.Investigations are at present carried out in order to study further structural properties of the Platinum-Coal systems.
    Notes: Es wurden ESR- und elektrische Widerstandsmessungen an Pt—C-Katalysatoren, die vorher auf Temperaturen zwischen 50 und 1000° C erhitzt worden waren, durchgeführt. Die temperaturabhängigen Änderungen der Parameter der ESR-Linien und des elektrischen Widerstandes sind eine weitere Unterstützung für die Hypothese der „pseudosandwich“-Komplexe zwischen Platin und Kohle, wobei ein ungepaartes Elektron vom Pt-Atom abgegeben wird.Zur Aufklärung weiterer struktureller Eigenschaften der Pt—C-Systeme sind zur Zeit noch Untersuchungen im Gange.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0935-6304
    Keywords: Multidimensional capillary GC ; GC-GC interface ; GC-tandem mass spectrometry ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The analysis of complex mixtures, such as essential oils requires high resolution chromatographic separation and even the use of very efficient columns cannot prevent the overlapping of certain peaks. This means that it is very difficult to obtain high quality mass spectra when the sample contains numerous constituants. The pre-separation by column or preparative GC leads to a considerable loss of material and, often, to the formation of artefacts. In order to overcome some of these difficulties, we have built a simple multi-column system that is connected to an MS-MS instrument. Two independent chromatographs equipped with capillary columns were connected. The interface, which consists of a modified PTV injector, gives the possibilities of direct transfer, back-flushing, heart-cutting, intermediate cold trapping, trace enrichment and selective sample introduction. These operations are controlled by a switching valve system (DANI-MFC 393 unit). The chromatographic system was first connected to a MS-MS instrument which may result in high MS and collision activated MS spectra.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Siloxane/silarylene copolymers as stationary phases ; OV-61-OH ; High temperature gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A commercially available silanol terminated silicone stationary phase, OV-61-OH (33% phenyl), and two phenyl-substituted siloxane/silarylene copolymers, Sila 3 (27% phenyl) and 4 (35% phenyl), have been evaluated for use as stationary phases in fused silica capillary columns for gas chromatography.Ulterations in column adsorptive activity, separation efficiency, stationary phase film thickness and selectivity after column conditioning for 50 h at 370°C have been studied. A high thermal stability was experienced with the stationary phases tested here. For OV-61-OH, the best thermal stability was obtained when coated on untreated fused silica, which illustrates the importance of grafting reactions here. The heat treatment resulted in some deactivation of adsorptive sites in the column. A higher degree of column deactivation was achieved when surface silylation was performed prior to coating. High thermal stability was achieved with Sila 3 when coated on such surfaces. Sila 3 would thus be preferred in cases when high thermal stability in combination with high dsorptive inertness is desired.Sila 4 showed low column bleeding at 370 °C, but prolonged heating at this temperature resulted in the broadening of n-alkane peaks when eluted at 90 °C. This indicates that excessive crosslinking has taken place during the heat treatment and the minimum allowable column operation temperature is thereby increased to ca. 120 °C. The separation of aza-arenes and of triglycerides are shown as applications.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0935-6304
    Keywords: Enantiomer separation ; mixed chiral selectors ; modified cyclodextrins ; gas chromatography ; PCB ; o,p´-DDD ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Columns containing different types of cyclodextrin derivatives have been evaluated for chiral gas chromatographic separation of atropisomeric PCBs, o,p´-DDT and o,p´-DDD. Separation was attempted on columns containing mixed chiral selectors, and the performance of two closely related selectors was also examined. The cyclodextrins were: permethylated-β-CD (PM-β-CD), heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-CD (2,3-M-6-TBDMS-β-CD), heptakis(2,3-di-O-methyl-6-O-tert-hexyldimethylsilyl)-β-CD (2,3-M-6-THDMS-β-CD), and heptakis(2,3-di-O-ethyl-6-O-tert-hexyldimethylsilyl)-β-cyclodextrin (2,3-E-6-THDMS-β-CD). The cyclodextrins were dissolved in OV-1701 or in a dimethylsiloxane/silarylene copolymer containing 5% phenyl in the backbone. The application of mixed chiral selectors led to improved separations, however; at most eleven PCB congeners were separated on a single column. Chiral resolution of o,p´-DDD was achieved. The use of a dimethylsiloxane/silarylene copolymer as a matrix for the cyclodextrins is a promising approach. With such a matrix, blocking of the CD cavities by silicone substituent groups can be avoided, and a reasonable CD solubility can be provided. The selectivity of heptakis(2,3-di-O-ethyl-6-O-tert-hexyldimethylsilyl)-β-CD and heptakis(2,3-di-O-methyl-6-O-tert-hexyldimethylsilyl)-β-CD was quite different, the former selector could separate four congeners, while the latter separated ten congeners.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 24 (1922), S. 60-66 
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Silanol terminated dimethylsiloxane/silarylene copolymers ; Silanol terminated dimethylpolysiloxane ; Thermal immobilization ; High temperature columns ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal stability of silicones can be improved on replacement of certain of the oxygen atoms in the polymer backbone by phenyl groups. Such a polymer has been synthesized and evaluated for use as stationary phase in fused silica capillary gas chromatography; the polymer was dimethyl substituted and silanol terminated. A selectivity was provided by the phenyl groups in the backbone. For comparative purposes, a silanol-terminated dimethylpolysiloxane has also been evaluated.Both stationary phases gave columns of highest separation efficiency and the supporting fused silica surface was deactivated by the stationary phases on thermal treatment. Further, low column bleeding was observed at the maximum temperature tested, 370°C. The phenyl-containing phase could be immobilized to 60% by heat treatment, but the pure dimethylpolysiloxane was 10% immobilized. The influence on immobilization of factors such as nature of the supporting surface, stationary phase silanol content, reaction temperature and atmosphere in the column during reaction has been studied.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0020-7381
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0040-4039
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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