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  • 1
    Electronic Resource
    Electronic Resource
    A study of HPLC separation and spectrophotometric, polarographic and voltammetric detection of 4-substituted derivatives of N-nitroso-N-methylaniline (1994)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 350 (1994), S. 678-683 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Optimised conditions have been found for the separation of N-nitroso-N-methylaniline derivatives substituted in the position 4 (4-R-NMA, where R =- H,- CH3, - OCH3, - Cl, - CN, - OH and - NO2), using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of aqueous 0.01 mol l−1 KH2PO4 with methanol (4+6) or acetonitrile (7+3), or a mixture of water, methanol, acetonitrile and 80% H3PO4 (200+200+200+3). Four detection techniques have been investigated: Direct UV photometry, polarography on a hanging mercury drop electrode, anodic voltammetry on a glassy carbon fibre array electrode and indirect anodic voltammetric detection after photolytic denitrosation of the analytes. The UV photometry is the most universal and yields limits of detection around 10−6 mol l−1. Polarography exhibits the poorest sensitivity (with a limit of detection of ca. 10−5 mol l−1) but it can be used for selective detection of 4-NO2-NMA. Direct voltammetric detection is selective for the oxidizable derivatives and the limits of detection attained are lower than those obtained by UV photometry (for 4-OH-NMA) or comparable with (for 4-OCH3-NMA). When the analytes are photolytically denitrosated to yield oxidizable derivatives, the voltammetric detection of 4-H-NMA, 4-Cl-NMA, 4-CH3-NMA and 4-NO2-NMA has limits of detection one order of magnitude lower than those obtained UV photometrically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323664
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Optimization of a GC-MS/MS Method for the Analysis of PCDDs and PCDFs in Human and Fish Tissue (2000)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 595-599 
    Details
    ISSN: 0935-6304
    Keywords: GC-MS/MS ; PCDDs ; PCDFs ; human tissue ; fish tissue ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---This paper outlines the possibilities of selectivity and sensitivity enhancement in measuring PCDD/F congeners using an ion trap GC-MS/MS. The pressure of the collision gas and the collision energy were optimized. The modified GC-MS/MS method was applied to the determination of PCDDs and PCDFs in human and fish tissues. Limits of quantification were about 1 pg/g of fat for all seventeen 2378 PCDD/Fs tested (starting amount of fat, 2 g).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    A split-disk, dual-electrode amperometric cell and its application to the detection of biogenic amines with galvanostatic activation of the glassy carbon working electrodes (1990)
    Weinheim : Wiley-Blackwell
    Electroanalysis 2 (1990), S. 443-448 
    Details
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A split-disk, dual-electrode amperometric cell was constructed and tested using biogenic amines as the model analytes. Advantages of the cell include a small working volume (less than 1.8 μL), favorable hydrodynamic conditions, and the fact that the system can be used in parallel-adjacent and series arrangements with the same geometry. The collection efficiency on the downstream electrode in the series arrangement is high (around 38% for reversible electrode reactions) and is very close to the theoretical value. The differences in the collection efficiencies for electrode reactions with different degrees of reversibility can improve the selectivity of measurement and assist identification of the substances. Selectivity is greatly improved in the parallel-adjacent arrangement where one electrode is activated by galvanostatic pretreatment while the other is only mechanically polished.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140020605
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Pretreatment of glassy carbon electrodes by anodic galvanostatic pulses with a large amplitude (1989)
    Weinheim : Wiley-Blackwell
    Electroanalysis 1 (1989), S. 405-412 
    Details
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glassy carbon electrodes (GCEs) can be activated by the passage of large-amplitude (for example, 20-mA) anodic galvanostatic pulses with durations shorter than 1 second. The increased activity stems from an increase in the rate of charge-transfer reactions and from the adsorption accumulation of the analytes on the electrode surface, which is demonstrated for catecholamines and ascorbic acid. As demonstrated by X-ray photoelectron and fast-atom-bombardment mass spectrometry, the galvanostatic treatment leads to an increase in the amount of chemisorbed oxygen. Scanning electron microscopy shows very small mechanical changes of the electrode surface. The activation effect depends on the composition of the test solution and the character of the analytes. There is an optimal electric charge that produces the highest electrode activity and lowers the limits of determination for catecholamines by approximately two orders of magnitude; on further increase in the charge, the electrode activity decreases (due to the formation of a thick layer of graphite oxide). The activation effects are less pronounced in flow-through measurements. The method can be readily implemented for the periodic, automated reactivation of glassy carbon electrodes, but the optimal conditions must be found experimentally for various systems.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140010505
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    A solid polymer electrolyte amperometric detector for FIA and HPLC with mobile phases of low conductivity (1992)
    Weinheim : Wiley-Blackwell
    Electroanalysis 4 (1992), S. 447-451 
    Details
    ISSN: 1040-0397
    Keywords: Flow cell ; resistive media ; nafion ; amperometric detection ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An amperometric cell with a small platinum wire working electrode, a submicroliter geometric volume, and a solid polymer electrolyte (Nafion) was constructed and tested. The cell permits sensitive and reliable detection even in mobile phases of negligible electric conductivity, (e.g., distilled water or nonpolar organic solvents). The sensitivity is substantially higher than that attained with similar cells containing large-are working electrodes; typical limits of detection amount to analyte concentrations between 10-7 and 10-6 mol/dm3, corresponding to subnanogram amounts in common HPLC sample volumes. The detector response exhibits satisfactory linearity, a linear dynamic range of at least three concentration decades, and a good precision, with relative standard deviations of 1 to 5%. This cell substantially widens the possibilities of amperometric detection, permitting direct application, for example, to normal-phase HPLC or to methods with programmed composition of the mobile phase (gradient elution).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140040410
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    Paper (German National Licenses)
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