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  • 1
    ISSN: 1520-6882
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 1520-6882
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Analytical chemistry 66 (1994), S. 635-644 
    ISSN: 1520-6882
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    ISSN: 1520-6882
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    ISSN: 1520-6882
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Microchimica acta 104 (1991), S. 337-351 
    ISSN: 1436-5073
    Schlagwort(e): supercritical-fluid chromatography ; mobile phase ; stationary phase ; carbon dioxide ; modifiers
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The effects of modifiers on the mobile-phase and the stationary-phase properties in packed-column supercritical-fluid chromatography were studied. Modifiers, may affect retention and improve peak shapes and efficiencies, because of (i) increased mobile-phase polarity, (ii) increased mobile-phase density, (iii) stationary-phase deactivation, and (iv) increased solvation or swelling of the stationary phase. In this paper these four parameters are evaluated and evidence to establish their relative importance is considered. The introduction of a modifier can lead to a substantial increase in the density of the mobile phase. The reliability of several methods for calculating the critical properties and densities of binary fluids is investigated. The Chueh and Prausnitz method gives the most accurate results for the calculation of the critical properties. The Lee and Kesler equation of state yields accurate density estimates. Adsorption isotherms have been measured on several stationary phases for packed-column SFC. These data suggest that stationary-phase deactivation is the most important effect of adding modifiers. Adsorption data on different stationary phases can also be used to judge their applicability. Relevant indicators are the maximum amount of modifier that can be adsorbed on the surface (saturation level) and the initial steepness of the isotherm (surface activity). The latter parameter can be related more closely to the peak shape observed in the absence of modifiers. All silica-based materials studied so far give rise to broad and highly asymmetrical peaks for certain classes of polar solutes. Different silica-based materials appear to differ in degree of activity, but the kind of interactions are the same. On a polystyrene-divinylbenzene stationary phase the mobile-phase modication effect could be studied without the interference of active sites.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 17 (1994), S. 325-334 
    ISSN: 0935-6304
    Schlagwort(e): Capillary electrophoresis ; Repeatability of electroosmotic flow ; Silica capillary tubes ; Column pretreatment ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The influence of a number of factors, such as the nature of the buffer, the presence of additives therein, the manufacturing conditions, and the pretreatment of the capillary, on the magnitude and repeatability of the electroosmotic flow (EOF) in silica capillary tubes has been investigated. It was established that the nature of the buffer plays the most significant role in respect of the stability and magnitude of EOF, whereas the conditions used for manufacture and pretreatment of the tubing are less important. The EOF obtained using buffers consisting of tris(hydroxymethyl)aminomethane and ethylenediamine was more repeatable than that obtained using pure phosphate buffers. Buffer additives such as sodium dodecylsulfate, 1-butanol, sodium salts of 1-pentanesulfonic acid and 1-heptanesulfonic acid, altered the magnitude of the EOF only, not its repeatability.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 17 (1994), S. 373-389 
    ISSN: 0935-6304
    Schlagwort(e): GC ; Natural gas analysis ; Sulfur components ; Selective enrighment ; Sulfur selective detection ; Calibration ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 475-482 
    ISSN: 0935-6304
    Schlagwort(e): Supercritical fluid chromatography, SFC ; Speed of analysis ; Secondary flow ; Pressure drop ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 413-418 
    ISSN: 0935-6304
    Schlagwort(e): On-line extraction-GC ; Phase-switching ; Open-tubular traps ; Stationary phase swelling ; Large volume injection ; PTV ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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