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  • Analytical Chemistry and Spectroscopy  (7)
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  • 1
    ISSN: 0935-6304
    Keywords: Gas chromatography, GC ; Glass capillary columns ; Free release static coating ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coating speed upon static coating of glass capillary columans was evaluated in terms of inner diameter and length of the column, viscosity and pressure of solvent vapor, etc. From the equation obtained it can be shown that a smaller diameter of a microbore column restricts solvent vapor transfer to the orifice of the column drastically. To compensate for this restriction, a higher pressure at the meniscus is needed. As an alternative to using a higher coating temperature, application of more volatile solvents such as n-butane and isobutane is proposed. Several glass capillary columns (130 μm i.d.) were coated with SE-54 dissolved inpentane-acetone mixed with n-butane or isobutane and the column performances were evaluated. Selection of these solvents permitted free release static coating of ca. 100 μm columns at lower or even ambient temperatures and they were equally suitable as commonly applied solvents (e.g. pentane) to coat highly efficient columns.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0935-6304
    Keywords: Fused silica capillaries ; Deactivation ; Silylation ; Aerobic conditions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new, simple procedure to deactivate fused silica capillaries without hydrothermal treatment is proposed. Based on high temperature reactions of octamethylcyclotetrasiloxane (D4) in the presence of oxygen, this procedure results, upon coating with dimethylsilicone (SE-30), in columns which give almost symmetric peaks for as little as 150 pg of critical compounds, such as decylamine, thereby demonstrating very high inertness. A mechanism of the deactivation procedure, which, in contrast to previously developed procedures, is based on thermal reactions under aerobic conditions, is proposed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron impact and chemical ionization (ammonia and methane) mass spectral behaviour of the cis- and trans-(2-hydroxycyclohexyl)-mercapturic acid methyl esters, metabolites of cyclohexeneoxide, was examined. Only with chemical ionization was it possible to differentiate between these two configurational isomers, by observing the stereoselective loss of H2O from the protonated molecular ions. Using this stereoselective process, a method was developed for the assessment of the relative amounts of stereoisomeric mercapturic acids, excreted as metabolites in the urine of rats treated with cyclohexeneoxide.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A stereospecific synthesis of N1-(2H3)-labelled R(-)-hexobarbital is described. A sensitive and rapid selected ion monitoring assay procedure for pseudoracemic hexobarbital, consisting of equal amounts of S(+)-hexobarbital (1a) and (2H3)-R(-)-hexobarbital (1b) in 100 μl blood samples of rats was developed. Both the parent enantiomers in blood and three major metabolites excreted in urine were quantified. An application of the method in rats is described, and the results are compared to previously obtained data of separately administered enantiomers.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0306-042X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron impact mass spectral behaviour of 14 synthetically prepared mercapturic acid methyl esters was examined. The most important and characteristic fragmentation reactions are discussed and special emphasis is made on the occurrence and the mechanism of two fragmentation pathways, which were recognized as ‘retro-Michael’ reactions. In principle, each reaction may result in the formation of two typical ions. In addition, three characteristic ‘key-ions’ originating from the N-acetyl(-l-)cysteine methyl ester part of the mercapturic acids were recognized in all mercapturic acid methyl esters investigated; these ‘key-ions’ can most probably be used as a tool for the qualitative as well as the quantitative analysis of mercapturic acids by gas chromatogra-phy mass spectrometry in biological fluids.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Extensive 13C and 15N labelling has shown that the molecular ions of 2-, 3- and 4-cyanopyridine with lifetimes up to 10-6 s eliminate hydrogen cyanide originating predominantly from the ring (˜65%). Moreover, this hydrogen cyanide loss occurs after an equilibrated positional interchange of the ring carbon atoms at positions interchange of the ring carbon atoms at positions 2, 4 and 6 via Dewar pyridine structures. In molecular ions with lifetimes of 10-6-10-5 s skeletal rearrangements have taken place in such a way that both nitrogen atoms have become equivalent prior to the loss of hydrogen cyanide. Arguments are put forward that this equivalence of nitrogen atoms is caused by the intermediacy of ions with a 1,4-dicyanobuta-1,3-diene structure. About 60% of these intermediate ions eliminate hydrogen cyanide in a fast process. The remaining 40% of these ions undergo ring closure again to a pyridine ring in which the carbon atoms of positions 2, 4 and 6 are positionally interchanged rapidly via Dewar pyridine structures followed by ring opening again and eventual loss of hydrogen cyanide. This interpretation of the 13C and 15N labelling results is further corroborated by a study of the loss of hydrogen cyanide from molecular ions of 1,4-dicyanobuta-1,3-diene labelled with 13C in both cyano groups.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0935-6304
    Keywords: Capillary columns ; Free release static coating procedure ; Acceleration of coating by polar solvents in the coating solution ; Calculation of relevant physical parameters ; Heat transfer into the capillary ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cause of an observed acceleration in the free release static coating process of a capillary when more polar solvents are added to alkanes as stationary phase solvents has been studied. By using a computer program, 9 of the relevant physical parameers were calculated in relation to the composition of the solvent hixtures. Curves of these parameters vs composition of the mixures were drawn. From the results it can be deduced that the change of these parameters with the increase of polar solvents in the solution, is probably insufficient to explain the drastic increase of the free release static coating speed. A physical model is proposed to calculate the depth of the meniscus around which sufficient heat can be transferred into the evaporating surface per unit time, to evaporate the solvent at a rate that the coating speed indicates. It is demonstrated that when pentane-acetone mixtures are used to coat a capillary, the depth of the meniscus indeed is greater than when pure pentane is used. The proposed model may lead to a better understanding of phenomena involved in the static coating process.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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