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  • 1
    ISSN: 1612-1112
    Keywords: Capillary electrophoresis ; Column technology ; Deactivation ; Polyethyleneoxides ; Ribonucleotides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1612-1112
    Keywords: Supercritical fluid chromatography ; Surface modification ; Deactivation ; Silica particles ; Stationary phases ; Packing materials ; Packed capillary columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 7 (1984), S. 329-332 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Fused silica capillary columns ; Deactivation ; Polymethylhydrosiloxanes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 8 (1985), S. 741-747 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Fused silica capillary columns ; Deactivation ; Cyanopropylhydrosiloxanes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 8 (1985), S. 378-384 
    ISSN: 0935-6304
    Keywords: Gas chromatography, GC ; Fused silica capillary columns ; Deactivation ; Phenylhydrosiloxanes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 9 (1986), S. 506-514 
    ISSN: 0935-6304
    Keywords: Supercritical fluid chromatography, SFC ; Deactivation ; Gas chromatography, GC ; Small diameter capillary columns ; Organosilicon hydrides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2016-06-07
    Description: 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.
    Keywords: SPACE RADIATION
    Type: 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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  • 8
    Publication Date: 2019-06-28
    Description: Dense materials, such as steel balls, continuously levitated with energy provided by efficient high-powered siren in combination with shaped reflector. Reflector system, consisting of curved top reflector and flat lower reflector, eliminates instability in spatial positioning of sample.
    Keywords: FABRICATION TECHNOLOGY
    Type: NPO-16146 , NASA Tech Briefs (ISSN 0145-319X); 8; 4; P. 570
    Format: text
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  • 9
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    In:  Other Sources
    Publication Date: 2019-06-28
    Description: Acoustic fields support and cool liquid particles. Levitated by sound energy, liquid drop in acoustic standing-wave field surrounded by acousticically-induced jet streams. Streaming gas cools drow below its freezing point in small fraction of second. Allows new amorphous alloys including "metallic glass" to be formed.
    Keywords: FABRICATION TECHNOLOGY
    Type: NPO-15658 , NASA Tech Briefs (ISSN 0145-319X); 7; 4; P. 472
    Format: text
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  • 10
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    In:  Other Sources
    Publication Date: 2019-06-28
    Description: After initial formation, spheroids processed without contaminating touch of solid objects. Spheroid in process supported by acoustic levitation at each work station and transported between stations by combination of acoustic levritation and acoustic propulsion. Automatic sequence of target-pellet fabication allows no contact of solid ojbect with spheroids in process. Potential for manufacture of precise microcapsules for catalysts and medications.
    Keywords: FABRICATION TECHNOLOGY
    Type: NPO-15592 , NASA Tech Briefs (ISSN 0145-319X); 7; 4; P. 471
    Format: text
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