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  • Computational Chemistry and Molecular Modeling  (6)
  • Solid-phase extraction  (4)
  • 42.75
  • 1995-1999  (11)
  • 1960-1964
  • 1920-1924
  • 1
    Electronic Resource
    Electronic Resource
    Data correlation in on-line solid-phase extraction-gas chromatography-atomic emission/mass spectrometric detection of unknown microcontaminants (1998)
    Springer
    Chromatographia 48 (1998), S. 273-283 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Atomic emission and MS detection ; Solid-phase extraction ; Aqueous samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A procedure is described for the (non-target) screening of hetero-atom-containing compounds in tap and waste water by correlating data obtained by gas chromatography (GC) using atomic emission (AED) and mass selective (MS) detection. Solid-phase extraction (SPE) was coupled on-line to both GC systems to enable the determination of microcontaminants at the 0.02–1 μg L−1 level in 7–50 mL of aqueous sample. The screening was limited to compounds present in at least one heteroatom-selective GC-AED trace above a predetermined concentration level. These compounds were identified by their partial formulae (AED) and the corresponding mass spectra, which were obtained from the GC-MS chromatogram via the retention index concept. The potential of the approach was demonstrated by the identification of target compounds as well as all unknowns present in tap and waste water above the predetermined threshold of 0.05 μg L−1 (tap water) or 0.5 μg L−1 (waste water).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467683
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  • 2
    Electronic Resource
    Electronic Resource
    On-line coupling of solid-phase extraction and gas chromatography with atomic emission detection for analysis of trace pollutants in aqueous samples (1995)
    Springer
    Chromatographia 40 (1995), S. 119-124 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Atomic emission detection ; Aqueous samples ; Solid-phase extraction ; Organophosphorus pesticides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An on-line, solid-phase extraction gas chromatography atomic-emission detection (SPE-GC-AED) system has been set up using an on-column interface to transfer 100 μl of desorbing solvent to the GC part of the system. Analytical characteristics such as recovery, precision and linearity of calibration plots were comparable with those of the off-line combination of SPE-GC-AED using organophosphorus pesticides as test compounds. The fully on-line set-up causes a marked improvement in detection because of the quantitative transfer of the analytes from the SPE module to the GC: detection limits are as low as 5–20 ng l−1 for the analysis of 10 ml raw and spiked surface water samples using the phosphorus channel. Detection levels can be further enhanced by processing up to 100 ml samples. The integrated analytical system is robust. The potential of the on-line set up has been demonstrated for the analysis of surface water and waste water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02272157
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  • 3
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    De edelherthorzel Cephenemyia auribarbis gekweekt (Diptera: Oestridae) (1999)
    In:  Nederlandse Faunistische Mededelingen (01692453) vol.9 (1999) p.109
    Details
    Publication Date: 2007-01-10
    Description: The rearing of the botfly Cephenemyia auribarbis (Diptera: Oestridae) After several failures we finally succeeded in rearing botflies Cephenemyia from third-instar larvae. From a red deer shot at 13 March 1998 about one hundred larvae of Cephenemyia auribarbis (Meigen, 1824) were collected. Ten individuals reached the pupal stage. After 22 days, one fullgrown male died in the pupa, and two males emerged and lived for 17 and 18 days respectively. This is one of the few recorded succesful attempts to rear botflies.
    Keywords: Insecta ; Diptera ; Oestridae ; Cephenemyia auribarbis ; Nederland ; Verspreiding ; 42.75
    Repository Name: National Museum of Natural History, Netherlands
    Type: Article / Letter to the editor
    Format: application/pdf
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    PAPER (OA)
  • 4
    Electronic Resource
    Electronic Resource
    On-line solid-phase extraction-gas chromatography-ion trap tandem mass spectrometric detection for the nanogram per liter analysis of trace pollutants in aqueous samples (1997)
    Springer
    Chromatographia 44 (1997), S. 372-380 
    Details
    ISSN: 1612-1112
    Keywords: Solid-phase extraction ; Gas chromatography ; Ion trap tandem mass spectrometry ; Water samples ; Environmental analysis ; Pesticides ; Bromide ; Nitrite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary On-line solid-phase extraction-gas chromatographyion-trap tandem mass spectrometry (SPE-GC-MS/MS) has been used for the trace-level determination of polar and apolar pesticides. The SPE-GC interface, an Autoloop 2000, was operated at an injection temperature of 90°C which permitted the determination of thermolabile pesticides such as carbofuran and carbaryl. Rectilinear calibration curves were obtained for the analytes tested over a range of 0.1–500 ng L−1, using a sample volume of 10–100 mL for enrichment on an SPE cartridge packed with styrene-divinylbenzene copolymer. The detection limits for the pesticides were in the 0.01–4 ng L−1 range. For a number of pesticides acceptable tandem mass spectra were obtained at levels as low as 0.1 ng L−1 level in real-life water samples. As a demonstration of the applicability of this technique for inorganic anions, bromide and nitrite were converted into 4-bromoacetanilide and 2-phenylphenol, respectively. The reaction products were pooled and subjected to simultaneous analysis by the present method using full-scan mass spectrometric detection. The detection limits were 0.3 and 2 ng L−1, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466313
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  • 5
    Electronic Resource
    Electronic Resource
    Automated derivatization for on-line solid-phase extraction-gas chromatography; phenolic compounds (1997)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 20 (1997), S. 363-368 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Solid-phase extraction ; Automation ; Water samples ; Acetylation ; Chlorophenols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An automated system for derivaatization was coupled on-line with solid-phase extraction-gas-chromatography (SPE-GC). The system was optimized for the determination of phenol and chlorinated phenols in aqueous samples. The test analytes were acetylated with acetic anhydride; proper buffering of the sample was a critical factor. Next, the phenol acetates were enriched on a SPE cartridge and transferred to a GC; two appraoaches were studied. In the first approach, the derivatives were enriched on disposable C18 cartridges (ASPEC type) and desorbed with methylacetate. Aan aliquot of the final eluate was injected on-line the GC by means of a loop-type interface. In the second approach, trace enrichment was performed on 10 × 2 mm i.d. LC-type precolumn packed with polystyrenedivinylbenzene copolymer (PLRP-S) this precolumn was dried with a mitrogen purge and the phenol acetates were desorbed with ethyl acetate which was injectedon-line into the retention gap of the GC under partially concurrent solvent evaporation (PCSE) conditions. The Derivatization-SPE-GC system which was based on the loop-type interface has the advantage of simplicity and easy operation, the main drawback is the impossibility to determine phenol acetates which elute prior to trichlorophenol acetates. With the derivatization-SPE-GC approach using PCSE-based desorption, even the most volatile analyte of the test series, phenol acetate, can be determined successfully. The entire procedure, including the derivatization step, was fully automated and integrated in one set-up. The precision data for the integrated on-line derivatization-SP-FID system were fully satisfactory, with RSD values of 1-12 % at the 1 μg/1 level. When a sample volume of 2.2 ml was analyzed, The detection limits for the chlorinated phenol acetates were in the 0.1-0.3 μg/1 range.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240200704
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  • 6
    Electronic Resource
    Electronic Resource
    Implementation of reaction field methods in quantum chemistry computer codes (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 16 (1995), S. 1445-1446 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540161113
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  • 7
    Electronic Resource
    Electronic Resource
    Solvatochromism of the π* ← n transition of acetone by combined quantum mechanical - classical mechanical calculations (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996), S. 1067-1076 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solvent shift of the π* ← n transition of acetone in water, acetonitrile, and tetrachloromethane was calculated in a combined quantum mechanical - classical mechanical approach, using both dielectric continuum and explicit, polarizable molecular solvent models. The explicit modeling of solvent polarizability allows for a separate analysis of electrostatic, induction, and dispersion contributions to the shifts. The calculations confirm the qualitative theories about the mechanisms behind the blue shift in polar solvents and the red shift in nonpolar solvents, the solvation of the ground state due to electrostatic interactions being preferential in the former, and favorable dispersion interaction with the excited state, in the latter case. Good quantitative agreement for the solvent shift between experiment (+1,700, +400, and -350 cm-1 in water, acetonitrile, and tetrachloromethane, respectively) and the explicit solvent model (+1,821, +922, and -381 cm-1) was reached through a modest Monte Carlo sampling of the solvent degrees of freedom. A consistent treatment of the solvent could only be realized in the molecular solvent model. The dielectric-only model needs reparameterization for each solvent. © 1996 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Calculations of molecules, clusters, and solids with a simplified LCAO-DFT-LDA scheme (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 58 (1996), S. 185-192 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simplified LCAO-DFT-LDA scheme for calculations of structure and electronic structure of large molecules, clusters, and solids is presented. Forces on the atoms are calculated in a semiempirical way considering the electronic states. The small computational effort of this treatment allows one to perform molecular dynamics (MD) simulations of molecules and clusters up to a few hundred atoms as well as corresponding simulations of condensed systems within the Born-Oppenheimer approximation. The accuracy of the method is illustrated by the results of calculations for a series of small molecules and clusters. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Direct reaction field force field: A consistent way to connect and combine quantum-chemical and classical descriptions of molecules (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1111-1132 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The direct reaction field (DRF) force field gives a classical description of intermolecular interactions based on ab initio quantum-chemical descriptions of matter. The parameters of the DRF force field model molecular electrostatic and response properties, which are represented by distributed charges and dipole polarizabilities. The advantage of the DRF force field is that it can be combined transparently with quantum-chemical descriptions of a part of a large system, such as a molecule in solution or an active site in a protein. In this study, the theoretical basis for the derivation of the parameters is reviewed, paying special attention to the four interaction components: electrostatic, induction, dispersion, and repulsion. The ability of the force field to provide reliable intermolecular interactions is assessed, both in its mixed quantum-chemical-classical and fully classical usage. Specifically, the description of the water dimer and the solvation of water in water is scrutinized and seen to perform well. The force field is also applied to systems of a very different nature, viz. the benzene dimer and substituted-benzene dimers, as well as the acetonitrile and tetrachloromethane dimers. Finally, the solvation of a number of polar solutes in water is investigated. It is found that as far as the interaction energy is concerned, the DRF force field provides a reliable embedding scheme for molecular environments. The calculation of thermodynamic properties, such as solvation energy, requires better sampling of phase space than applied here. © 1996 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Utopia dielectrica (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 523-531 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dielectric constant of a material is a macroscopic property that measures the reduction of the electrostatic forces between charged plates separated by the material, compared to a vacuum as intermediate material. It is next encountered as a scaling parameter in Coulomb's law for interacting charges, not only in the force, but also in the energy. In deriving the theory for dielectrics, the macroscopic nature is essential: Only then is the basic assumption that the dielectric material is homogeneous and isotropic a valid one. The appearance of the dielectric constant as a simple scaling factor in Coulomb's law has tempted many computational chemists to forget about the macroscopic nature of the dielectric and to apply the screened Coulomb's law between charges, supposedly in a low-dielectric medium such as proteins, in microscopic force fields. Optimization of force fields even led to distance-dependent “dielectric constants.” Another use of the dielectric constant appears in the dielectric continuum reaction field approaches for the computations of solvation energies and solvent effects. The solute is embedded in a cavity surrounded by the dielectric. Specific interactions between solvent molecules and solute are thus neglected. The cavity size and dielectric constants of interior and exterior are optimized for the model. The aim of this article is to show, by means of calculations on interacting point charges embedded in cavities surrounded by dielectrics and microscopic models of “low-dielectric” materials by explicit polarizabilities, that as far as the dielectric “constant” is concerned anything can happen, depending on the nature of the charges, the distance to the cavity boundary, the spatial arrangement of charges, and polarizabilities. Thus, a warning is issued to injudicious use of dielectric models in microscopic calculations. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560855
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