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  • Electronic Resource  (3)
  • 1990-1994  (2)
  • 1985-1989  (1)
  • Analytical Chemistry and Spectroscopy  (3)
  • 1
    ISSN: 0886-9383
    Keywords: Derivatization reaction ; Factorial design ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A number of nucleophiles have been successfully identified and quantified using the Kröhnke reaction with 2,3-diphenyl derivatives of quinolizinium salts. Optimization of the reaction conditions by means of a mathematical model involving analysis of the response surface has led to a better understanding of the factors exerting an influence on the above reaction.The parameters chosen were temperature, reaction time, base concentration, water concentration and nucleophile concentration. The reaction was developed in polar aprotic solvents (acetone, acetonitrile). To facilitate the nucleophilic attack, the presence of an organic base (triethylamine) was necessary, although concentrations in excess of 0·15M did not alter the development of the reaction. Since pharmaceutical solutions are often aqueous, the influence of water on the reaction was studied. Low water volumes have no significant influence on the opening of the quinolizinium ring by the nucleophilic reagent. However, when the water proportion exceeded that of the organic solvent, the fluorescence intensity was lower than expected. Development of the fluorescent reaction product was first detected 5 min after the reaction started. The fluorescence intensity reached its optimum value after 138 min.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Equilibration of hydrogen gas with the water in a variety of biological sample materials was carried out in Vacutainers using platinum-on-alumina catalyst physically isolated from the liquid water. The equilibration takes 3 days at room temperature - much slower than with catalysts which float on the water surface - but this reduces the short-term temperature sensitivity of the procedure, and the inexpensive materials used allow convenient disposal of biologically contaminated samples after analysis. The slow equilibration also allows time for complete exchange with water contained in a complex sample matrix such as plant stems or soil without the need for prior isolation of the water sample. The method has particular application in studies of human total body water where repeated studies can be carried out over a short time period without the need to wait for the previous dose to wash out. Water turnover rates from total diurnal energy expenditure studies measured by this method were not significantly different from those obtained by the zinc reduction method.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 13 (1986), S. 535-540 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metabolic profiling of urinary organic acids from patients with juvenile-onset (Type 1) diabetes mellitus have revealed significantly elevated levels of 2-hydroxybutyric acids. To test the hypothesis that these metabolites, as well as 4-deoxyerythronic acid, are derived from L-threonine, stable isotope-labeled threonine was infused into an insulin-deficient dog and the incorporation of 13C into these metabolites was monitored by gas chromatography/mass spectrometry. Electron ionization was relatively insensitive, but positive chemical ionization with ammonia as the reactant gas gave both protonated molecules and [M+NH4]+ ions, which could be analysed by selected ion monitoring. The isotope-labeled species of 2-hydroxybutyric, 4-deoxyerythronic and 4-deoxythreonic acids were observed, but 13C was not incorporated into other organic acids. Thus, it is proposed that L-threonine is a precursor of these metabolites.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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