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  • Articles: DFG German National Licenses  (15)
  • 1990-1994  (15)
  • 1
    Electronic Resource
    Electronic Resource
    A study of the adsorption activities of silanol surface structures on a fused silica model substrate by combining 29Si CP MAS NMR and inverse gas chromatographic data (1994)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 17 (1994), S. 77-84 
    Details
    ISSN: 0935-6304
    Keywords: Fused silica model substrates ; Adsorption characteristics ; Surface OH distribution ; Inverse gas-solid chromatography ; 29Si CP MAS NMR ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The possibilities of inverse gas-solid chromatography (IGC) in obtaining chromatographic data on fumed silica were examined. Aerosil A-200, a fused silica model substrate in 29Si nuclear magnetic resonance analysis, was trimethylsilylated to different degrees. IGC was used to very reproducibly determine the free specific energies of adsorption of several functionalized probe solutes. Hydrogen bonding solutes have a free specific energy of adsorption that is at least about 50% higher than that of non-hydrogen bonding probe solutes. NMR was used in combination with elemental analysis to calculate surface concentrations of the different chemical surface structures. IGC data and surface concentrations were combined in order to determine the contribution of each type of surface structure to the total free specific adsorption energy. It could be concluded that residual silanols from the reaction of dihydroxydi-siloxysiloxane (Q2 groups) with trimethylchlorosilane possess a higher adsorption activity than the silanols initially present.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240170207
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  • 2
    Electronic Resource
    Electronic Resource
    Possibilities and limitations of coiling induced secondary flow in capillary supercritical fluid chromatography (1990)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 475-482 
    Details
    ISSN: 0935-6304
    Keywords: Supercritical fluid chromatography, SFC ; Speed of analysis ; Secondary flow ; Pressure drop ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The possibility of enhancing radial mass transfer in capillary SFC by tightly coiling the column is discussed. The influence of coiling-induced secondary flow on the plate height and the speed of analysis in capillary SFC is investigated. It is shown that the experimental plate height in tightly coiled metal or fused silica columns departs from the Golay theory for laminar flow. The effect of the pressure drop associated with the use of higher mobile phase linear velocities is studied. The capacity factors of retained components are used as sensitive probes for pressure drop over the column. Experimental plate heights in coiled columns are compared with values calculated from Tijssen's theory for coiling induced secondary flow. At low velocities a good quantitative agreement was observed between the theory and the experimental results. At intermediate velocities only a qualitative agreement is found. The speed of analysis in coiled columns was found to be up to 5 times higher than in straight capillaries. The largest gain in analysis speed was obtained for solutes with low capacity factors. It is shown that coiling the column can have a positive influence on the detectability. For tightly coiled 210 μm i.d. columns the advantages of coiling-induced secondary flow could be fully exploited without adverse effects of the column pressure drop. For 50 μm columns the possibility to increase the speed of analysis by coiling was limited due to the high pressure drop.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240130707
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Supercritical fluid extraction-capillary gas chromatography: On-line coupling with a programmed temperature vaporizer (1990)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 669-673 
    Details
    ISSN: 0935-6304
    Keywords: Supercritical fluid extraction (SFE) ; On-line SFE-GC ; Programmed temperature vaporizer (PTV) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple and versatile system is described for the on-line coupling of SFE to capillary GC. The interfacing consists of a programmed temperature vaporizer (PTV) injector. With this injector it is possible to combine solute trapping, elimination of a high flow of extraction fluid, and quantitative transfer of solutes to the seperation column. The problems caused by impurities in the extraction fluid in on-line SFE-GC are discussed. Simple methods are described for the purification of commercially available carbon dioxide. The trapping efficiency of the PTV injector is studied. Applications of the SFE-PTV-GC system are given for the analysis of polymer anti-degradants, polar compounds, and samples with environmental relevance.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240131003
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  • 4
    Electronic Resource
    Electronic Resource
    The effects of the column pressure drop on retention and efficiency in packed and open tubular supercritical fluid chromatography (1991)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 14 (1991), S. 438-445 
    Details
    ISSN: 0935-6304
    Keywords: Supercritical fluid chromatography ; Pressure drop ; Retention ; Efficiency ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of the pressure drop across the column on retention and efficiency in SFC have been studied. Numerical methods are described which enable the prediction of hold-up time and pressure drop in both packed and open tubular columns. Predictions of both hold-up time and pressure drop are in good agreement with experimental data.The density gradient along the column can be calculated using the numerical methods and a procedure is described which enables the calculation of the overall capacity factors of the solutes from the density profile in the column. Significant variations of the capacity factor are observed along the column.The effect of the density gradient along the column on local diffusivity and dispersion is studied. The column efficiency in systems with significant pressure drops is affected by changes in: the linear velocity of the mobile phase; the diffusion coefficients; and the capacity factors of the solutes along the column. The overall efficiency of the chromatographic system can be calculated if, as is the case for open tubular columns, adequate plate height equations are available.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240140704
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  • 5
    Electronic Resource
    Electronic Resource
    Use of open-tubular trapping columns for on-line extraction-capillary gas chromatography of aqueous samples (1993)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 413-418 
    Details
    ISSN: 0935-6304
    Keywords: On-line extraction-GC ; Phase-switching ; Open-tubular traps ; Stationary phase swelling ; Large volume injection ; PTV ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The applicability of open-tubular trapping columns for on-line extraction-capillary GC analysis is evaluated. The extraction step involves sorption of the analytes from water into the stationary phase of an open-tubular column, removal of the water by purging the trap with nitrogen, and desorption of the analytes with an organic solvent. The effect of swelling of the stationary phase with organic solvents on the retention power of the trap is studied. When using pentane or hexane as swelling agent breakthrough volumes of at least 10 ml can easily be obtained for non-polar compounds. For a number of medium polarity compounds breakthrough volumes of 5 ml can be achieved when chloroform is used as the swelling agent. The required drying time is less than 1 minute. Quantitative desorption requires only 75 μl of organic solvent. Solvent elimination prior to transfer to the GC column is carried out using a PTV injector and a multidimensional GC system. The system is applied for the analyses of river water, urine, and serum samples.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240160706
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  • 6
    Electronic Resource
    Electronic Resource
    Quantitative aspects of directly coupled supercritical fluid extraction-capillary gas chromatography with a conventional split/splitless injector as interface (1993)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 425-428 
    Details
    ISSN: 0935-6304
    Keywords: On-line SFE-GC ; Split/splitless interface ; Quantitative aspects ; Discrimination ; Reproducibility ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quantitative aspects of on-line supercritical fluid extractioncapillary gas chromatography (SFE-GC) with a split/splitless injector as interface were investigated. Special attention was paid to the discrimination behavior and the reproducibility of the split/splitless interface. A simple experimental set-up is proposed that allows accurate quantitation in on-line SFE-split GC. The results obtained in on-line SFE-GC compare favorably with those from conventional GC with split injection. Discrimination was found to be absent when working at sufficiently high interface temperatures. Finally, the effects of the carbon dioxide flow rate, interface temperature and split ratio on both discrimination and reproducibility were studied.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240160709
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  • 7
    Electronic Resource
    Electronic Resource
    Use of a temperature programmed injector with a packed liner for direct water analysis and on-line reversed phase LC-GC (1993)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 459-463 
    Details
    ISSN: 0935-6304
    Keywords: LC-GC ; Aqueous samples ; Large volume injection ; PTV injector ; Solid-phase extraction ; Thermal desorption ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A system is described that allows the introduction of large volumes of water samples in capillary GC. Water elimination is carried out in the solvent split mode in a PTV injector with a packed liner. Two ways of separating water and analytes, i.e. evaporative and non-evaporative (solid-phase extraction), are compared. Sampling in the solid-phase extraction mode is favorable both in terms of recovery as well as with regard to sampling time. Quantitative recovery is obtained for priority pollutants ranging in volatility from dimethyl-phenol to phenanthrene. Losses occur for more volatile compounds, but even for these compounds the repeatability of the recoveries remains acceptable. With the system described here, water samples up to at least 1 ml of water can be directly analyzed. The detection limits are in the sub-ppb range.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240160803
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  • 8
    Electronic Resource
    Electronic Resource
    Determination of sulfur components in natural gas: A review (1994)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 17 (1994), S. 373-389 
    Details
    ISSN: 0935-6304
    Keywords: GC ; Natural gas analysis ; Sulfur components ; Selective enrighment ; Sulfur selective detection ; Calibration ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: More stringent environmental regulations as well as higher demands presently being imposed on the sulfur content of natural gas feed-stocks for chemical processes necessitate the development of new analytical procedures for sulfur determination in natural gas. Only analytical procedures based on gas chromatography can meet the sensitivity and accuracy requirements dictated by environmental regulation institutions and modern chemical industry. The complexity of the natural gas matrix as well as the extremely low concentration levels at which the sulfur species occur make the development of these analytical methods a true challenge. In this review the three steps common for analytical methods for trace analysis in complex matrices, i.e. pretreatment, chromatographic separation, and detection, are discussed in detail. Possible methods for calibration of the system are discussed in the final section.Various techniques to determine sulfur in natural gas are described. Depending on the application, the most suitable system has to be selected. For example, for on-line application in a hazardous area a simple and rugged system is required, i.e. a simple gas chromatograph with a flame photometric detector, while for laboratory application a more complex instrument including preconcentration, column switching, and more exotic detection systems could be more suitable. Therefore it is crucial to define the requirements of the instrument at an early stage and use the information in this review article to develop/select a dedicated instrument/procedure for the problem at hand.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240170603
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  • 9
    Electronic Resource
    Electronic Resource
    Introduction of large volumes of methylene chloride in capillary GC with electron capture detection (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 429-432 
    Details
    ISSN: 1040-7685
    Keywords: large volume injections ; PTV injector ; electron capture detection ; multidimensional gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, a system is presented that allows direct introduction of large volumes of methylene chloride in capillary gas chromatography (GC) using the electron capture detector (ECD). The system is based on a two-dimensional (one-oven) GC instrument equipped with a programmed temperature injector. During sample introduction, the solvent is eliminated via the split line. Residual traces of methylene chloride that enter the precolumn are eliminated via a column-switching device located between the precolumn and the analytical column. The system is used for the analysis of pesticides and polychlorinated biphenyls (PCBs) in methylene chloride at ultra low concentrations. The introduction of large sample volumes significantly improved the detection limits. Using the system described here, the solvent exchange step, normally necessary when the ECD is used to analyze samples containing methylene chloride as the solvent, is no longer required.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220050506
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    High-speed GC/MS using narrow-bore columns and ion trap detection (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 413-419 
    Details
    ISSN: 1040-7685
    Keywords: capillary GC ; narrow-bore columns ; GC/MS ; ion trap mass spectrometry ; detection limits ; working range ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fast gas chromatographic separations can be achieved by vacuum-outlet operation and by applying narrow-bore columns. In this work, the combination of 50 μm i.d. columns with ion trap mass spectrometric detection is evaluated. Detection limits in the electron ionization mode, and in the chemical ionization mode using CH4 as the reaction gas, are 1 pg and 5 pg, respectively. Owing to the high sensitivity of the ion trap mass spectrometer, a significant improvement in the working range in comparison with other detection systems is obtained. The small column flows cause no loss of mass spectral resolution and sensitivity. The performance of the system is demonstrated by the analysis of some real-world samples.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220050504
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    Paper (German National Licenses)
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