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  • 1
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A new technique is described for the direct detection of volatile organic compounds present in aqueous solutions at levels in the parts per trillion range. The sample is enriched in analyte in two consecutive stages; one utilizes a semi-permeable membrane interface and the other a jet separator. The analyte solution is sampled as it flows coaxially over a semi-permeable capillary membrane, the interior of which is continuously purged by helium. The permeate is pneumatically transported to the mass spectrometer via a jet separator, which is used to remove excess helium and 'vater from the analyte vapor strean. Data are reported for two instruments; in one the membrane/jet separator system is interfaced to a single ijuadrupolc mass spectrometer via a custom-built metal jet separator with a variable capillary gap. In the second, an ion-trap mass spectrometer is used in conjunction with a conventional fixed-gap quartz jet separator. Typical analyte response times are 2-5 min at ambient temperature, and Mow injection methods are used for sample delivery. Direct comparisons, made under identical instrumental conditions, show that the jet separator system displays even lowsr detection limits than a conventional direct-insertion membrane probe. Detection limits in the range 30 parlis per trillion to a few parts per billion are observed for selected volatile organic compounds and the response is linear over 3 orders of magnitude.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 25 (1987), S. 69-74 
    ISSN: 0749-1581
    Keywords: 2D heteronuclear multiple-quantum NMR ; Group assignment ; 13C and 1H shift measurements ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A two-dimensional heteronuclear multiple-quantum NMR experiment, based on the DEPT pulse sequence, for the simultaneous determination of the nature of proton-bearing chemical groups together with the measurement and correlation of carbon and proton chemical shifts is presented. Time and computer memory requirements for the proposed experiment are comparable to the acquisition of a two-dimensional C,H shift correlation spectrum. The data evaluation of the proposed zero-quantum carbon-shift correlated spectrum provides a list of chemical groups corroborated with their carbon and proton chemical shifts.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 25 (1987), S. 656-656 
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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