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  • Solvating gas chromatography  (3)
  • Deactivation  (2)
  • Life Sciences (General)  (2)
  • 2015-2019
  • 1995-1999  (7)
  • 1
    Electronic Resource
    Electronic Resource
    Peak capacity in packed capillary column solvating gas chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 333-337 
    Details
    ISSN: 1612-1112
    Keywords: Supercritical fluid chromatography ; Gas chromatography ; Solvating gas chromatography ; Peak capacity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In this paper, a general peak capacity expression was evaluated using columns containing various packing materials under solvating gas chromatography (SGC) conditions. Differing from column efficiency, peak capacity can describe both separation capability and speed when introducing the dead time into the peak capacity expression. Various factors that influence peak capacity in SGC are described, including particle pore size, chemical surface modification, particle size, column length, temperature, and pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467566
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Column wall modifications using polyethylene oxide for capillary electrophoresis of ribonucleotides (1999)
    Springer
    Chromatographia 49 (1999), S. 299-305 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF02467560
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    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
    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
    URL: http://dx.doi.org/10.1007/BF02267802
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  • 4
    Electronic Resource
    Electronic Resource
    Comparison of packed capillary solvating gas chromatography with supercritical fluid chromatography using carbon dioxide as mobile phase (1998)
    Springer
    Chromatographia 47 (1998), S. 673-677 
    Details
    ISSN: 1612-1112
    Keywords: Solvating gas chromatography ; Supercritical fluid chromatography ; Packed capillary columns ; Solvating power
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The efficiency (plate number per unit time) and elution power (range ofn-alkanes) of packed capillary SFC and SGC using CO2 as the mobile phase were compared. A higher plate number per unit time was obtained in SGC than in SFC using the same column under the same applied conditions. SGC is more suitable for fast separations than SFC. The solvating ability of the mobile phase, at the column exit end, decreased remarkably after the restrictor was removed. However, the elution molecular weight range in SGC can be greatly extended by increasing the column temperature.n-Alkanes with carbon numbers as high as 80 were separated under SGC conditions using a 35 cm ×250 μm i.d. column packed with 10 μm polymer-encapsulated silica particles at 200 atm, with a temperature program of 100–380°C at 10°C min−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467452
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  • 5
    Electronic Resource
    Electronic Resource
    Polybutadiene-coated zirconia packing materials in solvating gas chromatography using carbon dioxide as mobile phase (1999)
    Springer
    Chromatographia 49 (1999), S. 431-435 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Supercritical fluid chromatography ; Solvating gas chromatography ; Polybutadiene coated zirconia ; CO2 mobile phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In this paper, practical considerations of column efficiency, separation speed, thermal stability, and column polarity of capillary columns packed with polybutadiene-coated zirconia were investigated under solvating gas chromatography (SGC) conditions using carbon dioxide as mobile phase. When compared with results obtained from conventional porous octadecyl obtained from conventional porous octadecyl bonded silica (ODS) particles, PBD-zirconia particles produced greater change in mobile phase linear velocity with pressure than conventional ODS particles under the same conditions. The maximum plate number per second (Nt) obtained with a 30 cm PBD-zirconia column was approximately 1.5 times higher than that obtained with an ODS column at 100 °C. Therefore, the PBD-zirconia phase is more suitable for fast separations than conventional ODS particles in SGC. Maximum plate numbers per meter of 76,900 and 63,300 were obtained using a 57 cm×250 μm i.d. fused silica capillary column packed with 3 μm PBD-zirconia at 50 °C and 100 °C, respectively. The PBD-zirconia phase was stable at temperatures up to 320 °C under SGC conditions using carbon dioxide as mobile phase. Polarizable aromatic compounds and low molecular weight ketones and aldehydes were eluted with symmetrical peaks from a 10 cm column packed with 3 μm PBD-zirconia. Zirconia phases with greater inertness are required for the analysis of more polar compounds by SGC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467619
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  • 6
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    Skeletal response to corticosteroid deficiency and excess in growing male rats (1996)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The study was designed to investigate bone histomorphometric changes induced by corticosteroid deficiency and supplementation at different dose levels in the rat skeleton. Male rats were adrenalectomized (ADX) or sham-operated and divided into six groups. At 2 days after surgery, sham-operated control rats (CON + PLA) and one group of ADX rats (ADX + PLA) were implanted subcutaneously (s.c.) with placebo pellets. ADX rats in the remaining four groups (ADX + C25, ADX + C50, ADX + C100, and ADX + C300) were implanted sc with corticosterone pellets designed to release 25, 50, 100, or 300 mg of the hormone over a 60 day period. Each ADX rat was also implanted sc with an aldosterone pellet (2.5 mg) similarly designed to release its contents over the same time period. All rats were killed at 3 weeks after implantation of pellets. Terminal blood samples were collected for serum biochemistry and the proximal tibial metaphyses (PTM), tibial diaphyses, and first lumbar vertebrae (LV) were processed undecalcified for quantitative bone histomorphometry. A dose-dependent increase in serum corticosterone concentration was observed in ADX rats implanted with hormone pellets. In comparison to CON + PLA rats, ADX + PLA rats had lower cancellous bone volume associated with a stimulation in longitudinal bone growth, an increase in mineral apposition rate, and a trend for increased osteoclast and osteoblast surfaces in PTM. In contrast, cancellous bone of ADX + C25 rats was preserved at nearly the CON + PLA level. However, the higher doses of corticosterone increased cancellous bone mass, but decreased longitudinal bone growth and all indices of bone resorption and formation in a dose-dependent manner in PTM. Similar cancellous bone changes were observed in the LV of corticosterone-treated rats, with the exception of a lack of an hormonal effect on cancellous bone mass. In the tibial diaphysis, corticosterone inhibited periosteal bone formation in a dose-dependent manner, but did not affect cortical bone mass. The results indicate that corticosteroid deficiency induces cancellous osteopenia, whereas supplementation with a near physiologic dose of the hormone prevents this bone loss in ADX rats. Furthermore, corticosteroid excess inhibits bone growth and bone turnover in a dose-dependent manner, but does not induce cancellous osteopenia in growing male rats.
    Keywords: Life Sciences (General)
    Type: Bone (ISSN 8756-3282); Volume 19; 2; 81-8
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Adrenergic responsiveness is reduced, while baseline cardiac function is preserved in old adult conscious monkeys (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: To examine the physiological deficit to adrenergic stimulation with aging, five younger adult (3 +/- 1 yr old) and nine older adult (17 +/- 1 yr old) healthy monkeys were studied after instrumentation with a left ventricular (LV) pressure gauge, aortic and left atrial catheters, and aortic flow probes to measure cardiac output directly. There were no significant changes in baseline hemodynamics in conscious older monkeys. For example, an index of contractility, the first derivative of LV pressure (LV dP/dt) was similar (3,191 +/- 240, young vs. 3,225 +/- 71 mmHg/s, old) as well as in isovolumic relaxation, tau (24.3 +/- 1.7 ms, young vs. 23.0 +/- 1.0 ms, old) was similar. However, inotropic, lusitropic, and chronotropic responses to isoproterenol (Iso; 0.1 micrograms/kg), norepinephrine (NE; 0.4 micrograms/kg), and forskolin (For; 75 nmol/kg) were significantly (P 〈 0.05) depressed in older monkeys. For example. Iso increased LV dP/dt by by 146 +/- 14% in younger monkeys and by only 70 +/- 5% in older monkeys. Iso also reduced tau more in younger monkeys (-28 +/- 7%) compared with older monkeys (-13 +/- 3%). Furthermore, peripheral vascular responsiveness to Iso, NE, For, and phenylephrine (PE; 5 micrograms/kg) was significantly (P 〈 0.05) reduced in older monkeys. For example, phenylephrine (5 micrograms/kg) increased total peripheral resistence by 69 +/- 4% in younger monkeys and by only 45 +/- 3% in older monkeys. Thus in older monkeys without associated cardiovascular disease, baseline hemodynamics are preserved, but adrenergic receptor responsiveness is reduced systemically, not just in the heart.
    Keywords: Life Sciences (General)
    Type: The American journal of physiology (ISSN 0002-9513); 269; 5 Pt 2; H1664-71
    Format: text
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    NASA TECHNICAL REPORTS
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