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  • 1
    Electronic Resource
    Electronic Resource
    Mobile and stationary phases for SFC: Effects of using modifiers (1991)
    Springer
    Microchimica acta 104 (1991), S. 337-351 
    Details
    ISSN: 1436-5073
    Keywords: supercritical-fluid chromatography ; mobile phase ; stationary phase ; carbon dioxide ; modifiers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01245520
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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    High-speed narrow-bore capillary gas chromatography in combination with a fast double-focusing mass spectrometer (1995)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 517-524 
    Details
    ISSN: 0935-6304
    Keywords: GC/MS ; Scan speed ; Detection limits ; High-speed GC ; Narrow-bore columns ; High-resolution MS ; Sector mass spectrometers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work the application of high-speed narrow-bore capillary GC in combination with a fast scanning double focusing magnetic sector mass spectrometer is evaluated. Special emphasis is placed upon detection limits and scan speed in the full scan mode and in the selected ion monitoring mode (SIM). In the full scan mode, up to 20 scans per second could be obtained. The detection limits are in the low picogram range in the full scan mode and improve even to 5 to 50 fg in the SIM mode, depending on the sample complexity and mass resolving power. It will be illustrated that by increasing the resolution in the SIM mode, interferences from ions of the same nominal mass-to-charge ratio as the ions of interest are significantly reduced. Chemical background noise can therefore be largely eliminated, thus enhancing the signal-to-noise ratio.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240180903
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Large volume injection in capillary GC using PTV injectors: Comparison of inertness of packing materials (1995)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 124-128 
    Details
    ISSN: 0935-6304
    Keywords: Large volume injection ; PTV injector ; PTV solvent split injection ; Packed inserts ; Thermal degradation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240180213
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  • 8
    Electronic Resource
    Electronic Resource
    The Use of Non-Splitting Injection Techniques for Trace Analysis in Narrow-Bore Capillary Gas Chromatography (1998)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 491-497 
    Details
    ISSN: 0935-6304
    Keywords: Fast GC ; narrow-bore columns ; trace analysis ; splitless injection ; on-column injection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The use of hot splitless, cold splitless, and on-column injections for trace analysis in narrow-bore capillary GC is evaluated. Despite the low flow rates for the columns used, the required splitless times for splitless injections can be surprisingly short if liners with a small inside diameter are used. On-column injection can be applied by using an appropriate normal-bore precolumn coupled to the narrow-bore analytical column using a specially designed low dead volume column connector. The effects of the experimental conditions such as sample volume, injection temperature, and initial oven temperature on peak focusing and the discrimination and degradation behavior of the analytes are discussed. The possibilities to obtain sensitive and fast separations are illustrated by various applications.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Equilibrium-Sorptive Enrichment: A Novel Technique for Trace Analysis in Air (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 231-234 
    Details
    ISSN: 0935-6304
    Keywords: Trace analysis ; air samples ; BTX ; equilibrium-sorptive enrichment ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---No abstract
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Possibilities and Limitations of Fast Temperature Programming as a Route towards Fast GC (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 509-513 
    Details
    ISSN: 0935-6304
    Keywords: Fast GC ; fast temperature programming ; resistive heating techniques ; short columns ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---One possible way to speed up a gas chromatographic analysis is the application of fast temperature programming by using resistive heating techniques. With this heating technique programming rates up to 20° per second can be reached. A relative standard deviation of retention times better than 0.2% is obtained. Using fast temperature programming the analysis-times of a mineral oil sample, an industrial oligomer sample, and toxic compounds in diesel fuel have been reduced 5 to 20 times, compared to a standard temperature programmed analysis. In most cases resistive heating cannot be applied to reduce the analysis time of a complex sample. The use of fast temperature programming is preferable to the use of short columns and columns operated at above-optimum carrier gas velocities.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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