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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 683-688 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Recycle gas chromatography ; Microvalve ; Connectors ; Band broadening and peak distortion ; Activity ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sources leading to band broadening and peak distortion have been studied in a capillary column recycle system, based on a commercial microvalve. The ferrule system was a major contributor to band broadening. It was found that the quality of connections is very critical but the internal volume of the valve is not important. The pressure pulses resulting from each switching operation produced some band broadening with substances that had just been transferred through the valve but no adverse effects were noticed when they had travelled some distance into the column. Flow into valve cavities and through tees also produced a drop in efficiency. It is not clear whether this is solely due to problems in column connection or if changes in flow pattern also contribute.The activity of the valve toward polar substances was also assessed. No attempt was made to deactivate valve surfaces. The components of the Grob test mixture were almost unaffected but highly polar and acidic compounds such as nitrophenol showed severe losses. No evidence for catalysis was found.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 656-658 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary columns ; Open split interface ; GC/MS ; Benchtop mass spectrometer ; 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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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 597-605 
    ISSN: 0935-6304
    Keywords: GC/MS ; Automated data processing ; Pattern recognition ; Arson analysis ; Volatiles ; Petroleum ; Accelerants ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The analysis of residual accelerants in fire debris is commonly carried out by a three-step procedure: sample preparation; separation and detection; and data interpretation. Each of these steps can be optimized individually but successful analysis requires that they are compatible with each other. The isolation of residual accelerant from fire debris requires that several methods are used to cover the range of fueis that are commonly used by arsonists. Since almost all incendiary fires are set with petroleum based fuels such as gasoline or heating oil, analysis is targeted toward hydrocarbons. Capillary column gas chromatography on apolar phases is now the overwhelmingly predominant method of separation. Data interpretation is commonly carried out by visual comparison of chromatograms.Fire debris analysis presents some unique challenges that are not often encountered in other fields. The analyte may be present at only trace levels and pyrolysis products from building materials or furnishings may dominate chromatographic patterns. Synthetic polymers may act as precursors to hydrocarbons that compete with substances typically found in petroleum based fuels. Exposure to heat and other environmental factors may also generate severe distortions in the chromatographic profiles of accelerants.Unfortunately, there is no simple solution to these problems. Methods are available to reduce some of the chemical noise introduced by interferences and thus enhance the recognizability of the target substances. Mass spectrometry, in combination with a modern data system, is the most effective approach to filter out unwanted substances. The interpretation of the analytical results is aided by scaling, side-by-side comparison, or stacking of chromatograms. An additional advantage of such computerized systems is the possibility of complete automation of the analysis.In this communication, we look at the interplay of chromatographic resolution, noise reduction by mass spectrometry, and automated data evaluation. Examples from model experiments and from simulated arson samples are presented.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 27 (1995), S. 691-701 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of 3,4-dihydro-2H-pyran (DHP, C5H8O) has been investigated by two methods: in shock waves with the laser-schlieren technique using mixtures of 5 and 10% DHP in krypton over 900-1500 K, 110-560 torr; in a flow tube having a reaction pressure 0.5 torr above atmospheric using the decomposition of allylethyl ether as an internal standard, and covering 663-773 K. The retro-Diels-Alder dissociation to the stable acrolein and ethylene is the dominant channel for all conditions. Precise rate constants (rms deviation of 10%) were obtained for this process over the indicated temperature ranges. Unimolecular falloff is evident in the shock-tube results, and RRKM calculations also predict a slight falloff at the lower temperatures. These RRKM calculations use a routine vibration model transition state and agree closely with the high-temperature data when 〈ΔE〉down is a fixed 400 cm-1. Arrhenius expressions for k∞ derived from the two measurements are in close accord and also consistent with most previous studies of this reaction. © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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