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  • 1
    Digitale Medien
    Digitale Medien
    Column wall modifications using polyethylene oxide for capillary electrophoresis of ribonucleotides (1999)
    Springer
    Chromatographia 49 (1999), S. 299-305 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Capillary electrophoresis ; Column technology ; Deactivation ; Polyethyleneoxides ; Ribonucleotides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary In this study, a variety of fused silica capillaries with different combinations and sequences of treatments with HMDS and polyethylene oxide were prepared in order to develop an optimized column modification method for analysis of ribonucleotides. The 12 most common ribonucleotides (UTP, CTP, ATP, GTP, UDP, CDP, ADP, GDP, UMP, CMP, AMP, and GMP) in human cells were used as test solutes. Column performance measurements, including electroosmotic flow (EOF), solute migration speed and retention, column efficiency, peak shape, and resolution were investigated. By analyzing solute migration speed and retention of various hydrophilic/hydrophobic solutes, the column wall effects (EOF and adsorption) can be distinguished. This analysis method can give guidance in optimizing polymer coating properties (hydrophilicity/hydrophobicity) for CE columns. By studying the performance of these columns after various surface treatments, we were able to improve the separation of ribonucleotides from real samples to within 16 minutes with high efficiency and stability (over 300 analyses) using columns first deactivated with hexamethyldisilazane, and then coated with polyethylene oxide.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467560
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  • 2
    Digitale Medien
    Digitale Medien
    Polymethylhydrosiloxane surface deactivation of silica particles for packed capillary column supercritical fluid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 665-670 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Supercritical fluid chromatography ; Surface modification ; Deactivation ; Silica particles ; Stationary phases ; Packing materials ; Packed capillary columns
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Spherical porous silica particles (10 μm diameter, 300 Å and 80 Å pores), spherical nonporous silica particles (10 μm diameter), and irregular porous silica particles (≈10 μm diameter, 80 Å pores) were deactivated with polymethylhydrosiloxane (PS). The surface activities of the deactivated silica particles were investigated using various polar compounds under supercritical fluid chromatography (SFC) conditions (neat CO2), and compared with a commercial C18-bonded phase. The small pore (80 Å) silica particles could be more completely deactivated than larger pore (300 Å) and nonporous silica particles. The success of the PS deactivation method is ascribed to the excellent match between the reactive groups on the polymer backbone and the silica surface, and the formation of a highly crosslinked polymeric layer over the surface. Physical processes, such as adsorption and desorption of the deactivation reagent on the surface and diffusion from the surface, were found to have important effects on the deactivation. Using capillary columns packed with PS deactivated silica particles, typical polar organic compounds, including hydroxyl-containing compounds, carbonyl-containing compounds, free amines, and free carboxylic acids, were separated by SFC and compared with results from a commercial C18-bonded phase. While the results clearly show that the PS deactivated particles were more inert than the C18-bonded phase, better deactivation methods are still needed for separation of free acids and alkylamines.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02267802
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  • 3
    Digitale Medien
    Digitale Medien
    Deactivation of fused silica capillary columns with polymethylhydrosiloxanes (1984)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 7 (1984), S. 329-332 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; Fused silica capillary columns ; Deactivation ; Polymethylhydrosiloxanes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240070608
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  • 4
    Digitale Medien
    Digitale Medien
    Deactivation of fused silica capillary columns with cyanopropylhydrosiloxanes (1985)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 8 (1985), S. 741-747 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; Fused silica capillary columns ; Deactivation ; Cyanopropylhydrosiloxanes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A method is described for surface deactivation and modification of fused silica capillary columns with a cyanopropyl-containing reagent. The deactivation procedure involved a dehydrocondensation reaction between a bis(cyanopropyl)methylhydropolysiloxane reagent and surface silanol groups at an optimum temperature of only 250°C. Actual critical surface tension measurements were made using the capillary rise method. Excellent deactivation for acidic and basic compounds at the low ng level, and wettability for nonpolar and polar polysiloxane stationary phases were obtained. A procedure was developed to remove acidic impurities that are present in polar stationary phases.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240081109
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  • 5
    Digitale Medien
    Digitale Medien
    Deactivation of fused silica capillary columns with phenylhydrosiloxanes (1985)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 8 (1985), S. 378-384 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography, GC ; Fused silica capillary columns ; Deactivation ; Phenylhydrosiloxanes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this work, an investigation of new organosilicon hydride reagents with phenyl functional groups for deactivation and surface modification of fused silica capillary columns is described. Different reagents were tested for their ability to deactivate the fused silica surface, and actual critical surface tension measurements were made using the capillary rise method. The deactivation procedure required lower optimum temperatures than conventional methods. Deactivated capillaries and coated capillary columns were prepared and tested for reproducibility, efficiency, and surface inertness towards basic and acidic compounds at the low nanogram level.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240080803
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  • 6
    Digitale Medien
    Digitale Medien
    Deactivation of small diameter fused silica capillary columns with organosilicon hydrides (1986)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 9 (1986), S. 506-514 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Supercritical fluid chromatography, SFC ; Deactivation ; Gas chromatography, GC ; Small diameter capillary columns ; Organosilicon hydrides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small diameter fused silica capillary columns (50-75 μm i.d.) were deactivated at relatively low temperatures (250-300°C) with a mixture of polymethylhydrosiloxanes and several lowmolecular-weight organosilicon hydrides. Reproducible surface deactivations of highest quality were achieved with the polymethylhydrosiloxane (PMHS) reagent. Deactivations performed with PMHS via dynamic coating with neat or diluted reagent were evaluated by gas chromatography. Deactivations achieved with organosiloxane mono-, tri-, and tetrahydrides were also evaluated and compared. Low-molecular-weight organosilicon hydride deactivations were less time consuming and required lower head pressures for filling and coating columns with the reagent. Critical surface tensions of capillary surfaces modified with PMHS and the low-molecular-weight organosilicon hydrides gave support to the dehydrocondensation reaction between silica surface silanols and silyhydride bonds of the reagents. Slopes from Zisman plots indicated that coverage of the surface ranged from highest for the polymer (PMHS) to lowest for the monomers (TMS and PMDS). Efficiency measurements showed the influence that surface modification had on the uniformity and stability of the coated capillary columns. Well-deactivated capillary columns permitted the chromatography of polar solutes using supercritical carbon dioxide as mobile phase.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240090904
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  • 7
    facet.materialart.
    Unbekannt
    Diffusive electron acceleration at SNR shock fronts and the observed SNR radio spectral indices (1986)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The radio synchrotron emission from relativistic electrons in shell supernova remnants (SNRs) provides a unique opportunity to probe the energy distribution of energetic electrons at their acceleration site (SNR shock fronts). This information provides insight into the acceleration mechanism(s). The implications of these observations for the diffusive (first-order Fermi) acceleration of electrons at the SNR shock fronts are discussed.
    Schlagwort(e): SPACE RADIATION
    Materialart: NASA. Goddard Space Flight Center Nineteenth International Cosmic Ray Conference. Conference Papers: Invited Rapporteur, Highlight, Miscellaneous, Volume 9; 4 p
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
    facet.materialart.
    Unbekannt
    On the anomalous component (1985)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The so-called anomalous cosmic ray component, which occurs at energies of about 10 MeV/nucleon and consists only of He, N, O, and Ne, has been a subject of interest for more than a decade. The origin of this component is generally considered to be interstellar neutral gas that is ionized and accelerated in the solar wind. The mechanism and the location for the acceleration, however, remains an unsolved problem. A model is used which includes the effects of gradient and curvature drifts and considers the implications of observed spatial gradients of the anomalous component for the location of the acceleration region. It is concluded that if drifts are important the acceleration region cannot lie at the solar poles. It is also concluded that there is no single region for the acceleration which can account for both the observed intensities and gradients in models which include drift effects.
    Schlagwort(e): SPACE RADIATION
    Materialart: SH-4.6-6 , 19th Intern. Cosmic Ray Conf - Vol. 5; p 180-183; NASA-CP-2376-VOL-5
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
    facet.materialart.
    Unbekannt
    A simple model for the formation of 'reflected', 'intermediate', and 'diffuse' ion distributions upstream of earth's bow shock (1985)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Detailed energetic ion and low-frequency wave experiments on ISEE 1, 2, and 3, have established correlations between the types of ion populations and waves observed to exist in the earth's foreshock region. The present calculation has the objective to quantitatively test the picture obtained for the earth's foreshock region. An analysis is conducted of the coupled spatial and temporal evolution of upstream protons and hydromagnetic waves by means of a simple model in which the protons are represented by counterstreaming beams which resonate with hydromagnetic waves, exciting the outward propagating modes and damping the inward propagating modes at a single wave number.
    Schlagwort(e): SPACE RADIATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 90; 39-45
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
    facet.materialart.
    Unbekannt
    Hydromagnetic waves and cosmic-ray diffusion theory (1975)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: Pitch-angle (and energy) diffusion of cosmic rays in hydromagnetic wave fields is considered. The treatment remains strictly within the quasi-linear approximation. It is shown that the popular assumption of an isotropic power spectrum tensor of magnetic fluctuations requires in this case equal forms and magnitudes of Alfven and magnetosonic wave spectra - a situation which is generally unlikely. The relative contributions to the pitch-angle diffusion coefficient from the cyclotron resonances and Landau resonance due to the different types of waves are evaluated for a typical situation in the solar wind. Since the Landau resonance in this approximation also does not lead to particle reflections, a proper consideration of the nonlinear particle orbits is indeed necessary to overcome the well-known difficulties of quasi-linear scattering theory for cosmic rays near 90 deg pitch angle.
    Schlagwort(e): SPACE RADIATION
    Materialart: Astrophysical Journal; 198; June 1
    Format: text
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