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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Monatshefte für Chemie 116 (1985), S. 889-899 
    ISSN: 1434-4475
    Keywords: Gas solid chromatography ; High silica molecular sieves ; Low-boiling organic compounds ; Preconcentration ; Specific retention volumes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract High silica molecular sieves (silicalite, ZSM-5) were tested as adsorbents for gas chromatographic trace analysis. Therefore the retention behaviour of low-boiling organic compounds (hydrocarbons, halogenated hydrocarbons, amines, alcohols and ethers) on these materials was investigated. The specific retention volumes at different temperatures have been determined and elution orders and peak shapes were studied. The retention data allow a simple calculation of the breakthrough volumes (dynamic adsorption capacity) and the chromatographic characterisation of the adsorbents. Both nitrogen and oxygen containing compounds could not—or at least unreproducibely—be eluated up to 300°. The elution order and the peak shape of compounds with the same number of carbon atoms but different geometric and electronic structure (e.g.n-butenes;n-hexane, cyclohexane, benzene) can be explained by the action of exclusion effects and different diffusion barriers. On the basis of calculated breakthrough volumes we conclude that silicalite should be useful in the preconcentration of both saturated C3–C6 hydrocarbons and C1–C2 chlorinated hydrocarbons from gaseous streams.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 352 (1995), S. 535-536 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The fundamental suitability of solid-phase microextraction (SPME) has been investigated for the enrichment of partially well water-soluble and differently substituted polar nitrophenols. Two commercially available fibers coated with 100 μm polydimethylsiloxane or 85 μm polyacrylate, respectively, were compared with regard to the efficiency of the enrichment of these compounds. For all the compounds investigated, polyacrylate fiber showed a better affinity when the exposure time was longer in comparison with polydimethylsiloxane fiber. The ‘salting-out’ and the enrichment at low pH-values increased the sensitivity of the process significantly.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 587-592 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Headspace ; Solid phase microextraction ; Retention index ; Monoterpenes ; Pinus ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The applicability of solid phase microextraction (SPME) to the headspace analysis of monoterpene hydrocarbons from conifer needles was examined. To this end, the influences of fiber coating thickness, exposure time, and exposure temperature on the enrichment of the different monoterpene hydrocarbons were investigated. The distribution constants between polydimethylsiloxane fiber and gas phase at a given temperature were found to be very different. A relation is therefore derived to calculate the distribution constants of substances not available from their Kováts retention indices. A slightly different approach could be the use of so-called “relative distribution factors”, not considering the actual volume of fiber coating. In view of the different enrichment conditions in SPME as well as the general problems of headspace analysis, a comparison with a completely different method of sample preparation is presented. Furthermore, some applications of SPME to the analysis of monoterpenes from pine needles are given.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 20 (1997), S. 217-221 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Headspace solid phase microextraction ; Retention index ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The applicability of the retention index system to hcadspacc solid phase microextraxtion (HS-SPME) was investigated. In headspace SPME, the two equilibria gas phase/matrix and fiber coating/gas phase have to he considered. In this paper the equilibrium fiber coating/gas phase is discussed separately to characterize it more detailed and to investigate several methodical aspects. Therefore, the different distribution constants Kfiber/gas of n-alkanes, which were used for reference compounds, were related to their Kováts retention indices. The validity of the derived linear relationship log Kfiber/gas versus retention index I is demonstrated for various examples. This relation is helpful for the assessment of distribution constants of substances not available and for the choice of a suitable fiber coating. Furthermore, quantification of analytes in the gas phase can be done without authentic substances.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 239-242 
    ISSN: 0935-6304
    Keywords: Capillary GC ; Residential furnaces ; Brown coal ; Emission condensate ; PAH derivatives ; PAH retention index ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0935-6304
    Keywords: Liquid chromatography ; dead time ; multiparametric least-squares adjustment ; homologous series ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In reversed phase liquid chromatography (RP-HPLC), the validity of a multiparametric non-linear least-squares regression iterative method for the determination of the column dead time tM and the regression parameter (slope b), based on the use of alkan-2-ones, alkyl aryl ketones, and 1-nitroalkanes has been evaluated. The determination of tM and b has been extensively studied for two mobile phase systems acetonitrile-water and methanol-water on seven octadecyl-C18 and one octyl C8 analytical columns. The calculated tM and b values were compared with those obtained by Guardino's and Grobler's methods. The influence exerted thereon by the nature of the homologous series, the mobile phase composition, and the packing materials were investigated.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 333-337 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Serially coupled columns ; Selectivity optimization ; Optimization criterion ; Dual oven GC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved optimization criterion has been introduced for computer assisted optimization of selectivity of two different capillary columns coupled in series and placed in two independently heated ovens. The suitability of this criterion, which incorporates the change of resolution power with the change of working conditions, has been verified by simultaneously tuning the temperatures of two columns differing in retention mechanism for separation of isomeric branched C8 hydrocarbons.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 635-642 
    ISSN: 0935-6304
    Keywords: Capillary GC ; Emission control ; Humid samples ; Adsorptive sampling ; Hydrophobic adsorbents ; Thermal desorption ; Volatile organic compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Adsorptive enrichment on hydrophobic adsorbents, thermal desorption, and capillary gas-chromatographic analysis have been used to determine volatile organic compounds in extremely humid stack-gas emissions from the residential burning of brown-coal briquets. One hundred and fifty two compounds were identified and quantified. Quantitative emission factors were determined for the identified individual compounds in relation to the amount of the fuel used. These factors enable a first assessment of the pollution of the city of Leipzig with volatile organic compounds resulting from the burning of indigenous lignite.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0935-6304
    Keywords: Liquid chromatography ; retention index ; multiparametric least-squares adjustment ; homologous series ; nitramines ; nitroaromatics ; aminoaromatics and nitrophenols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In reversed phase liquid chromatography, the retention indices of some neutral and acidic explosives and related compounds (nitramines, nitroaromatics, aminoaromatics, and nitrophenols) based on the alkan-2-one, alkyl aryl ketone, and 1-nitroalkane retention index standards have been determined by the application of a new mathematical adaptation method, viz. a multiparametric least-squares regression iterative method. This method was applied to two types of columns. The first group includes six octadecyl-C18 columns with different packing materials and obtained from different manufacturers, while the second group comprises one octyl-C8 column. The retention indices have been extensively studied using either methanol-water or methanol-phosphate buffer mobile phase systems. The calculated multiparametric retention indices values were compared with those obtained by Guardino's, Grobler's, and Kovàts' methods. The influences of the concentration of the organic modifier in the mobile phase, aqueous mobile phase pH, and the column packing material on the retention indices of the explosives were also investigated. Good agreement was observed between the retention indices calculated by the use of the four mathematical methods for both neutral and acidic explosives.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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