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  • Analytical Chemistry and Spectroscopy  (5)
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  • Analytical Chemistry and Spectroscopy  (5)
  • Chemistry  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 19 (1990), S. 465-474 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Leukotrienes (LT) C4, E4 and N-acetyl-E4, their respective monomethyl esters and 14,15-2H2 analogs have been synthesized. The collisionally activated decompositions of the [ M + H] + and [ M - H] - ions formed by fast atom bombardment (FAB) have been studied by tandem mass spectrometry using a hybrid sector/quadrupole instrument. Structurally informative product ion spectra were obtained for each analyte; the fragmentation pathways proposed are consistent with the parallel data obtained for labeled and derivatized species. Fragmentation of [ M + H] + ions occurs prominently via cleavage of the thioether linkage with charge retention on the cysteine-containing (predominant for LTC4) or lipid-derived (predominant for LTE4) moieties. More pronounced differences were observed between the fragmentations of [ M - H] - ions derived from LTC4 and LTE4; the preference for charge retention, however, parallels that observed for the fragmentation of [ M + H] + ions. Selected ion monitoring during continuous-flow FAB mass spectrometric analysis of authentic LTC4 indicated a low-picogram detection limit.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 13 (1986), S. 605-609 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect has been investigated of data smoothing on the precision and accuracy of peak height ratio (analyte/isotopically-labelled internal standard) determination by gas chromatography/mass spectrometry with dual ion monitoring. The smoothing routines evaluated were all based on the moving average principle but differed with respect to weighting factors and filter width. Smoothing was shown to achieve only a minor improvement in precision and introduced significant bias in the peak height ratio calculation. In contrast, determination of response ratios by linear regression of analyte and internal standard signals achieved superior precision without the introduction of significant bias.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 12 (1985), S. 19-24 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new approach to dual metastable peak monitoring has been developed, based on synchronous switching of the accelerating voltage and electric sector voltage of a double-focusing mass spectrometer. The technique has been applied to the determination of oestradiol-17β as the bis(tert-butyldimethylsilyl) ether, using the 2H3 analogue as internal standard. The detection limit was approximately 5 pg during monitoring of the [M]+.→[M-C4H9]+ fragmentation. Analyses of plasma extracts indicated that greater selectivity of detection was achieved during metastable peak monitoring than during high resolution (8000) selected ion monitoring of the parent ion.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 3 (1989), S. 217-221 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Sequential daughter-ion-scanning analyses of small peptides have been performed using a hybrid tandem instrument of BEqQ configuration. Precursor ions are selected by B and allowed or induced (by high-energy collisional activation) to decompose in the region preceding E. Decoupling of E from the accelerating voltage permits the selection of the first-generation daughter ion whilst retaining appropriate float voltages for the quadrupole assemblies. The daughter ion selected by E is further subjected to low-energy collisional-activation dissociation (CAD) in q and the fragment-ion spectrum is obtained by scanning Q. The sequential daughter-ion-scanning technique has been used to establish that ‘internal’ fragments of the types, (AY′) and (BY′), are formed via initial Y-type cleavage. Fragmentation of a protonated peptide (angiotensin III) by loss of the C-terminal amino acid residue, yielding a (Bn′ + OH) ion, is reported for the first time. This process is analogous to that previously described for metal-cationized peptides.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 11 (1984), S. 415-420 
    ISSN: 0306-042X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A MAT 731 mass spectrometer has been modified to permit multiple ion monitoring at resolutions of 8000-10 000. The greater imprecision in response ratio (analyte/internal standard) determinations which accompanies the increase in mass spectrometric resolution is attributable to the weaker signal detected, rather than to instrument instability. The mass spectrometer has been coupled to a microprocessor-based data system and software prepared to facilitate the precise determination of response ratios. Imprecision is markedly reduced when isotope ratios are determined by linear regression analyses of signals attributable to the two ionic species detected.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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