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  • 1
    Digitale Medien
    Digitale Medien
    A continuous two-phase reaction system coupled on-line with capillary chromatography for the determination of polar solutes in water (1992)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 15 (1992), S. 242-248 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Capillary GC ; On-line extractive alkylation ; On-line acylation ; Carboxylic acids ; Amines ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Gas chromatographic procedures are described for the determination of carboxylic acids and chlorinated anilines in water samples.Propionic acid and 2,6-difluorobenzoic acid in aqueous solution have been simultaneously alkylated and extracted by means of a continuous two-phase reaction system, and then quantitated by on-line coupled capillary gas chromatography; tetrahexyl-ammonium hydrogen sulfate was used as phase transfer catalyst and pentafluorobenzyl bromide as reagent.A factorial design approach was used to optimize on-line derivatization of aqueous propionic acid with regard to pH and concentration of phase transfer catalyst. Alkylation and extraction, under optimized conditions, followed by quantitation of the pentafluorobenzyl ester by flame ionization detection furnished a linear calibration for concentrations between 0.1 and 10 μg/ml. The relative standard deviation was 9-15 %.The continuous two-phase reaction system was also used to determine (chlorinated) anilines present in water at concentrations of 0.1-1 μg/ml; pentafluorobenzoyl chloride was used as reagent and analysis was performed by capillary gas chromatography with flame ionization or electron capture detection. The on-line acylation of p-chloroaniline was optimized with regard to pH, reagent concentration, and reaction time.The on-line reaction system worked satisfactorily for both applications, although excess reagent caused some problems with the chromatography.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240150408
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  • 2
    Digitale Medien
    Digitale Medien
    The derivatization of fatty acids by (chloro)alkyl chloroformates in non-aqueous and aqueous media for GC analysis (1992)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 15 (1992), S. 785-790 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Capillary GC ; Derivatization ; (Chloro)alkyl chloroformates ; Non-aqueous reaction media ; Aqueous reaction media ; Fatty acids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Fatty acids can be conveniently derivatized in less than one minute with (chloro)alkyl chloroformates such as methyl chloroformate, 2-chloroethyl chloroformate and 2,2,2-trichloroethyl chloroformate. 2,2,2-Trichloroethyl chloroformate is the most reactive reagent, and yields a reaction product which can be sensitively detected by GC ECD (detection limit 50 ng/ml, i.e. 25 pg/injection, for C8, C10, and C12 acids).In non-aqueous media 3-picoline, N-methylpiperidine, and dimethylaminopyridine show catalytic activity comparable with that of pyridine and can, therefore, replace it. N-methylpiperidine is the best basic catalyst in aqueous media (i.e. media containing up to 40 % water).
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240151203
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  • 3
    Digitale Medien
    Digitale Medien
    Fully automated water analyzer based on on-line solid phase extraction-gas chromatography (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 303-315 
    Details
    ISSN: 1040-7685
    Schlagwort(e): capillary GC ; solid phase extraction ; membrane disks ; water samples ; automation ; nitrogen-phosphorus detection ; mass selective detection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An automated procedure for the analysis of aqueous samples by membrane disk extraction coupled on-line to capillary gas chromatography (GC) is presented. Organophosphorus pesticides are preconcentrated from aqueous samples on three 0.5 mm thick, 4.0 mm diameter XAD-2 membrane extraction disks which are mounted in a polymer holder for use in a PROSPEKT sample processor. The layers are dried by a stream of nitrogen (30 min at ambient temperature). Desorption of the analytes is carried out with ethyl acetate which is directly introduced into a retention gap under partially concurrent solvent evaporation conditions, using an early solvent vapor exit. The method is a fully software-controlled automated system, and includes sample preparation, sample transfer and GC analysis. The final analysis is carried out by GC with nitrogen-phosphorus (NPD) or mass-selective detection. The technique is applied to the determination of a series of organophosphorus pesticides in tap water and water from European rivers. With a sample volume of only 2.5 mL, the detection limits achieved with the NPD were 20-50 ng L-1 in tap water and 20-100 ng L-1 in river water.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mcs.1220050403
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  • 4
    Digitale Medien
    Digitale Medien
    A continuous liquid-liquid extraction system coupled on-line with capillary gas chromatography for environmental and ecotoxicological analysis (1997)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 20 (1997), S. 325-332 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Capillary GC ; Continuous liquid-liquid extraction ; Environmental applications ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The applicability of a liquid-liquid extraction system which is coupled on-line with a capillary gas chromatograph was studied for environmental and ecotoxicological analyses. The optimized and automated system was used for the determination of apolar and rather non-volatile organic compounds in aqueous samples. Relevant aspects of sample introduction, phase separation and selection of extraction solvent are discussed. Three routine-tipe applications are described, viz. an improved method for the determination of hexachlorocyclohexanes in ground water and the determination of the so-called NCC-ether and ACC-ether in ecotoxicological studies. Depending on the application studied, the concentration levels varied from 0.1 to 6000 μg/I, using ECD and/or FID detection. Typical coefficients of variation obtained with the total extraction-GC procedure were 2-25%.The system was found to be rugged, it saves time compared with set-ups involving off-line liquid-liquid extraction and considerably reduces the manual work load.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240200606
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  • 5
    Digitale Medien
    Digitale Medien
    Use of a Drying Cartridge in On-Line Solid-Phase Extraction-Gas Chromatography-Mass Spectrometry (1998)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 450-456 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Drying cartridge ; gas chromatography ; solid-phase extraction ; microcontaminants ; water samples ; on-line SPE-GC ; mass spectrometric detection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---A drying cartridge was used and optimized for the in-line elimination of water from the desorption eluent in on-line solid phase extraction-gas chromatography (SPE-GC). The cartridge is essentially a small stainless-steel precolumn packed with a drying agent which can be regenerated by simultaneous heating and purging with a moisture-free gas. The drying cartridge was mounted on an additional valve instead of between the SPE-GC transfer valve and the on-column injector to enable regeneration of the cartridge during the GC run and, thus, to increase sample throughput. Three drying agents were tested, viz. sodium sulfate, silica, and molecular sieves. Although molecular sieves have the highest capacity, silica was preferred because of practical considerations. Large-volume injections were performed through the in-line drying cartridge using a mixture of 23 microcontaminants ranging widely in polarity and volatility. Four solvents were tested. With pentane and hexane, the more polar analytes were retained by the drying cartridge. Ethyl acetate and methyl acetate gave much better (and closely similar) recoveries for all analytes. Because water elimination on the silica cartridge proved to be less critical than with ethyl acetate, this solvent was finally selected. The entire SPE-drying cartridge-GC set-up was combined with mass spectrometric (MS) detection for the determination of a mixture of micropollutants in real-life water samples. With 10-ml tap water samples spiked at the 0.5 μg/l level, for the majority of the test compounds the analyte recoveries generally were 60-106%, and (full-scan) detection limits typically were 0.01-0.03 μg/l. Some very polar analytes such as, e.g. dimethoate, were (partially) sorbed onto the silica packing of the drying cartridge.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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