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  • 1
    Electronic Resource
    Electronic Resource
    Identification of chlorophyll transformation products in zooplankton faecal pellets and marine sediment extracts by liquid chromatography/mass spectrometry atmospheric pressure chemical ionization (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 1177-1183 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Liquid chromatography/mass spectrometry with an atmospheric pressure chemical ionization interface permits the routine study of mixtures of algal-derived, chlorophyll transformation products isolated from biological and environmental samples. Interpretation of the mass spectra of standards of chlorophyll a and three of its commonly occurring transformation products has allowed the identification of components found in extracts from zooplankton faecal pellets and a marine surface sediment. This highly sensitive technique should prove valuable for pigment analysis in environmental studies.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290091218
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  • 2
    Electronic Resource
    Electronic Resource
    A computer-based method to increase the signal-to-noise ratio of negative-ion currents in double-charge-transfer spectroscopy (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 1502-1506 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Double-charge-transfer spectroscopy is routinely used to measure double-ionization energies of molecules to singlet and triplet electronic states of dications, but is experimentally difficult to apply because the yield of negative ions generated in the double-electron-capture reactions is low. The use of a data-acquisition system and repetitive scanning of a spectrum can increase signal-to-noise ratios, but the number of scans that can be acquired is limited by drifting in the spectrum position, which results in spectral-peak broadening. This limitation has been overcome in the present investigation by the application of a computer enhancement program that effectively superimposes successive spectra which are subject to slight drift. Spectra obtained for H+ projectile ions reacting with hexafluorobenzene (C6F6) molecules are presented; use of the program with such spectra reveals features in the computer-enhanced spectrum which are not clearly evident in the individual spectra.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290091508
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  • 3
    Electronic Resource
    Electronic Resource
    Doubly charged positive ions of chromium hexacarbonyl and molybdenum hexacarbonyl: Calculated and measured electronic-state energies (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 601-607 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Double-charge-transfer spectroscopy was used to measure the double-ionization energies of chromium hexacarbonyl and molybdenum hexacarbonyl molecules to triplet electronic states of the corresponding dications. The spectra were interpreted using data calculated using a modified MSXα method. The measured double-ionization energy to the ground triplet state is 22.8 ± 0.5 eV for Cr(CO)6 and 22.4 ± 0.5 eV for Mo(CO)6; both values match, within experimental error, an earlier measurement of 22.8 ± 0.5 eV for W(CO)6. The spectra for the three hexacarbonyls are remarkably similar, probably reflecting that the electronic structures of the three molecules are almost identical in the valence region. The similarity is reflected in the calculated data; the Coulomb repulsions between the two positive holes which characterize the dictations' states are 4.54, 4.44 and 4.45 eV for Cr(CO)62+, Mo(CO)62+ and W(CO)62+, respectively. These values correspond to the repulsive energy for two single charges separated by just over 3 Å, this separation being consistent with the size of the molecules.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300411
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  • 4
    Electronic Resource
    Electronic Resource
    Identification of Fenton's reagent-generated atrazine degradation products by high-performance liquid chromatography and megaflow electrospray ionization tandem mass spectrometryContribution 269, Environmental Toxicology Center, University of Wisconsin, Madison, WI 53706, USA. (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 452-460 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: High-performance liquid chromatography megaflow electrospray tandem mass spectrometry (HPLC/ES-MS/MS) with an on-line radioisotope detector was used to identify [2,4,6-14C] atrazine degradation products generated by treatment with Fenton's reagent (Fe2+ and H2O2). Fenton's reagent produced dealkylated and/or partially oxidized [2,4,6-14C] atrazine products in preference to dechlorinated products. Seven major products were identified by collision-induced dissociation spectra: 4-acetamido-2-chloro-6-(isopropylamino)-s-triazine, 4-amino-2-chloro-6-(isopropylamino)-s-triazine, 4-acetamido-2-chloro-6-(ethylamino)-s-triazine, 6-amino-2-chloro-4-(ethylamino)-s-triazine, 4-acetamido-6-amino-2-chloro-s-triazine, 2-chloro-4,6-diamino-s-triazine and the first report of 4-acetamido-2-hydroxy-6-(isopropylamino)-s-triazine. HPLC/ES-MS/MS provided a rapid method for identifying a wide range of atrazine transformation products in aqueous samples and obviated the need for fraction collection, extraction, and chemical derivatization of the more polar atrazine products. Furthermore, because analyte retention times in HPLC/UV and HPLC/ES-MS/MS were similar, compound identities determined using the latter could be directly assigned to peaks in UV chromatograms.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300309
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  • 5
    Electronic Resource
    Electronic Resource
    Combined experimental and computational study of the double ionization of ethylamine, propylamine and butylamine to triplet electronic states of their dications (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 1694-1700 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vertical double-ionization energies of ethylamine, propylamine and butylamine molecules to triplet electronic states of their dications were measured by double-charge-transfer spectroscopy. The energies to the lowest states of the dications were calculated using an ab initio method with four basis sets. The calculated values predicted fairly well the reduction in the lowest energy observed when the length of the substituted alkyl group increased. Double-ionization energies to the lowest and higher lying triplet states of the dications were calculated by application of a semi-empirical form of the multiple scattering Xα method. Even though several spectral peaks may only be identified with transitions to groups of closely lying states, the calculated data gave an insight into the electronic transitions which take place to give the double-charge-transfer spectra.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190301209
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  • 6
    Electronic Resource
    Electronic Resource
    Carbon-13 NMR investigations of three fluorinated steroids (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 501-505 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; solid-state NMR ; 13C NMR ; magic angle spinning ; steroids ; fluorinated compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-resolution carbon-13 NMR spectra were obtained for three solid fluorinated steroids. Assignments were carried out using several approaches, including two-dimensional spectra of the compounds in solution. Solid-state and solution-state chemical shifts are compared. Signals from one of the fluorine-containing carbons in each compound show the effect of interplay between shielding, dipolar and indirect scalar (J) coupling tensors. One sample is found to be a mixture of two polymorphic forms.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260330702
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  • 7
    Electronic Resource
    Electronic Resource
    Use of cross-polarization in lithium-6 solid-state NMR (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 152-155 
    Details
    ISSN: 0749-1581
    Keywords: Lithium-6 ; Cross-polarization ; Solid-state NMR ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cross-polarization (CP) magic angle spinning (MAS) 6Li—{1H} spectra were acquired for three different inorganic lithium compounds. Spectra with a good signal-to-noise ratio can be obtained in reasonable times. The poorer signal-to-noise ratios shown by spectra acquired in the same experimental time by means of a single pulse experiment are explained by the longer values of T1(6Li) in comparison with T1(1H). The determination of these values allows the acquisition parameters to be optimized. In particular, the optimum experimental conditions are discussed, taking into account the pulse delay, the number of transients and the total time of the experiment. Finally, a standard for 6Li—1H CP matching is proposed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260330213
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  • 8
    Electronic Resource
    Electronic Resource
    79,81Br effects in the high-resolution 13C NMR spectra of solid bromoaromatic compounds: Dipolar and indirect (79,81Br, 13C) interactions studied by ‘Inverse’ first-order perturbation theory (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 603-606 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; solid-state NMR ; magic angle spinning ; quadrupolar interactions ; perturbation theory ; bromine-carbon coupling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Splittings in the 13C cross-polarization magic angle spinning spectra of 1, 4-dibromobenzene and 4-bromo-3, 5-dimethylpyrazole are reported. They arise from (79,81Br, 13C) interactions influenced by the quadrupolar nature of the bromine nuclei. They are analysed using both ‘inverse’ perturbation and exact theories to yield data on both isotropic and anisotropic coupling, including the signs. The spectra also enable the sign of the bromine quadrupole coupling constant to be confirmed as positive.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260330720
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  • 9
    Electronic Resource
    Electronic Resource
    Editorial (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. S2 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260331303
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