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  • 1
    Electronic Resource
    Electronic Resource
    TAFTA: Assuring its Compatibility with Global Free Trade (1997)
    Oxford, UK and Boston, USA : Blackwell Publishers Ltd
    The @world economy 20 (1997), S. 0 
    Details
    ISSN: 1467-9701
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Law , Economics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1467-9701.00089
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of Melatonin on the Sleep-Independent Component of Prolactin Secretion (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of pineal research 8 (1990), S. 0 
    Details
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Sleep has a stimulatory effect on prolactin secretion. Recent studies in the human suggest the hypothesis that prolactin has also an endogenous sleep-independent rhythm, which can be influenced by endogenous melatonin. To investigate this hypothesis, the prolactin response to nighttime exposure to bright light was studied in eight women in detail. Light exposure induces a decrease in nocturnal melatonin secretion. It was demonstrated that exposure to bright light for 2 h at night caused a decrease in prolactin secretion, which surpassed significantly the decline one would expect by sleep deprivation only (P 〈 0.01). This was associated with a similar decline in melatonin secretion. Fall and rise of prolactin secretion under these conditions were always preceded by decrease and rise in melatonin levels in all eight women studied. Based on these observations, it is concluded that melatonin is associated with an endogenous circadian component of prolactin secretion. As specific melatonin receptors have been identified in the human nucleus suprachiasmaticus, which is the “master” circadian pacemaker, the observed phenomenon might be mediated through this structure. An alternative explanation of our findings could be based on the fact that melatonin influences dopamine metabolism, which in turn alters prolactin secretion. It can also not be ruled out that melatonin might act via the opioid system, which then could affect prolactin secretion. The total secretory activity for both hormones (area under the curve) did not change under experimental conditions, when compared to a control group. This suggests that acute light exposure and sleep deprivation influence the secretory process rather than the synthesis of these two hormones. This is in agreement with the observation that changes in natural light exposure throughout the year do alter the amplitude, but not the total amount of melatonin secreted. Further studies are needed to answer the question of melatonin storage definitively, as it is commonly believed that melatonin is immediately released after synthesis. It is concluded that melatonin through its external modulator light might entrain the circadian sleep-independent component of prolactin secretion and via its action on prolactin could modulate reproductive processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-079X.1990.tb00669.x
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  • 3
    Electronic Resource
    Electronic Resource
    Laser mass spectrometry of the Di-, Tri- and tetrachlorobenzenes: Isomer-selective ionization and detection (1994)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 8 (1994), S. 381-384 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The resonant two-photon ionization spectra of the S1←S0 transition of all di-, tri- and tetrachlorinated benzene isomers, cooled by supersonic jet expansion, are presented. As the spectra are well structured and isomer specific, this technique allows selective ionization of a single isomer out of mixtures such as, for example, environmental samples. Reflectron time-of-flight mass spectrometry is used for the mass-selective detection of the ions.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290080508
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Erste Ergebnisse einer Ringanalyse zur Erstellung eines internen Buchenblatt-Referenzmaterials für Ökosystemuntersuchungen (1989)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 334 (1989), S. 323-325 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary To evaluate pollution effects on ecosystems, more and more plant and animal samples are analyzed for their concentrations of pollutants and nutrient elements. Since chemical analyses of biological materials are largely influenced by matrix effects, their accuracy depends on the availability of reference materials. Unfortunately only very few such standards exist so far. The described interlaboratory comparison of beech leaves from Baden-Württemberg demonstrates the possibility of producing reference materials from selected organisms, which — though not certified — are sufficient for research projects. Apart from their function as reference materials, those standards show typical levels of elemental concentrations for their region of origin. First results are introduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00488475
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  • 5
    Electronic Resource
    Electronic Resource
    A Novel Interface for Optimized Coupling of Gas Chromatography and Supersonic Jet Spectroscopy (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 391-394 
    Details
    ISSN: 0935-6304
    Keywords: REMPI-TOFMS ; laser mass spectrometry ; supersonic jet ; GC-MS ; interface ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The laser-based methods Laser Induced Fluorescence (LIF) and Resonance-Enhanced Multi-Photon Ionization (REMPI) can be used as highly selective detection modes for gas chromatography (GC). One major prerequisite for successful application of these detection methods is the availability of appropriate and reliable interfaces between the GC effluent and the molecular beam inlet. When a pulsed supersonic molecular beam (jet) source is used, the analyte molecules are efficiently cooled, allowing maximum selectivity of the laser spectroscopic detection methods. However, several technical problems have to be solved for practical realization of a GC-supersonic jet valve hyphenation. The pulsed jet interface should not interfere with the GC properties and the supersonic molecular beam properties. Further a good working cycle for the conversion from the continuously flowing GC current to the pulsed jet gas flow should be attained. This paper presents a novel setup of a GC-pulsed jet interface. The construction allows temporal and spatial compression of the analyte molecules in jet gas pulse and thus an increase of the detection sensitivity. Moreover, the GC effluent comes into contact only with glass surfaces and not with valve parts like plungers and seals. This reduces memory effects and sample decomposition. The valve setup is tested with a REMPI-TOFMS instrument.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 6
    Electronic Resource
    Electronic Resource
    Hyphenation of gas chromatography and resonance-enhanced laser mass spectrometry (REMPI-TOFMS): A multidimensional analytical technique (1997)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 20 (1997), S. 461-470 
    Details
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Time-of-flight mass spectrometry ; Hyphenated analytical techniques ; REMPI laser ionization ; Selective ionization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Analysis of environmental samples usually requires time consuming sample preparation and clean-up procedures prior to instrumental detection. Faster analysis requires an enhanced instrumental selectivity in order to reduce the necessary clean-up effort. In this context we present a novel concept for coupling gas chromartography/mass spectrometry (GC-MS) with high resolution UV spectoscopy to increase selectivity. We use UV-laser induced, resonance-enhanced multi-photon ionization (REMPI)as a compound specifie ion source for time-of-flight mass spectrometry (TOFMS). The REMPI ionization involves the UV absorption spectroscopy into the ionization process as an aditional analytical dimension. The heart of the GC-REMPI-TOFMS coupling is a specially designed valve, which repetitively (20 Hz) expands the chromatographic eluent as short supersonic jet gas pulses (≈ 150 μs duration) into the vacuum of the mass specrtrometer. The sample molecules are cooled down to temperatures of 10-40 K within the jet expansion. Under these conditions, UV absorption spectriscopy (i.e. REMPi spectroscopy) becomes highly compound selective, even able to distinguish isomeric compounds. The ions formed by REMPI ionization are mass analyzed in the TOFMS. Thus the GC-REMPI-TOFMS coupling presented here is actually a three-dimensional analytical instrument, providing gas chromatographic (retention time) as well as mass spectrometric (molecular mass) and UV -spectroscopic (excitation laser wavelength) selectivity. In combination with gas phase sampling and concentration techniques for semi-volatile organic air pollutants based, e.g., on silicone rubber traps the GC-LAMS technique can be a powerful tool for fast environmental target analysis, e.g. for industrial emission control purposes.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240200902
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    Paper (German National Licenses)
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