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  • 1
    ISSN: 0935-6304
    Keywords: Gas chromatography-mass spectrometry ; Capillary columns ; Stationary phases ; Silicones ; Thermal degradation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The applicability of capillary columns for gas chromatography is often limited by stationary phase degradation at elevated temperatures. In order to achieve a better understanding of column thermostability, column bleed products have been analyzed qualitatively by gas chromatography-mass spectrometry (GC-MS). Three silicone stationary phases were studied: SE-52, SE-54, and OV-1701. Each of these was immobilized in the columns. The proportion of cyclics containing diphenyl in column bleed from SE-52 reflected to a large extent the composition of the polymer, while for SE-54 the proportion of such cyclics was unexpectedly high. The polar moiety of OV-1701, the cyanopropyl(phenyl)siloxy unit, was found to exert a highly destabilizing effect on the polymer, and the thermal degradation products consisted mainly of cyclosiloxanes containing this unit.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0935-6304
    Keywords: Open tubular gas chromatography ; Dynamic headspace analysis ; Purge and trap ; Thermal desorption ; Reinjection ; Fourier transform infrared spectroscopy ; Volatile constituents in polymers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An analytical system for the analysis of volatiles entrained in polymers is described. This system is based on a thermal desorption oven connected to a cold trap. After enrichment of headspace vapor, trapped material is reinjected and analyzed by open tubular gas chromatography/Fourier transform infrared spectroscopy, OTGC/FTIR. The thermal desorption oven is designed to provide different modes of sample introduction: use of a pyroprobe; insertion of a piece of quartz tubing with applied sample; or syringe injection. Headspace enrichment is carried out in a piece of fused silica capillary tubing filled with glass beads. The trap may be cooled either electrically using Peltier elements or with liquid nitrogen. A six-port rotary valve is used for flow switching between enrichment and reinjection modes. All system parameters, temperatures, and timed events, are controlled from the gas chromatograph. Dynamic headspace analysis is demonstrated as a method for polymer characterization.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: [Fephen2X2] complexes can be prepared in a good crystalline form by splitting off 1,10-phenanthroline from the corresponding [Fephen3]X2 salts with acetone or other organic solvents, or by reaction of proper anhydrous iron(II) salts or their pyridine complexes [Fepy4X2] with two moles 1,10-phenanthroline in hot, absolute pyridine. [Fephen2X2] complexes with X = Br, Cl, SCN, SeCN, OCN, N3, HCOO, CH3COO are high-spin compounds with magnetic moments between 5.1 and 5.3 B. M. [Fepy4F2], on the other hand, reacts with 1,10-phenanthroline to give only a 1:1 complex [FephenF2]n, which probably is polymeric.
    Notes: [Fephen2X2]-Komplexe erhält man in gut kristalliner Form durch Abspaltung von 1, 10-Phenanthrolin aus entsprechenden [Fephen3]X2-Salzen mit Aceton oder anderen organischen Lösungsmitteln oder bei der Reaktion geeigneter wasserfreier Eisen(II)-Salze oder ihrer Pyridinkomplexe [Fepy4X2] mit zwei Mol 1,10-Phenanthrolin in heißem, absolutem Pyridin. Die [Fephen2X2]-Komplexe mit X = Br, Cl, SCN, SeCN, OCN, N3, HCOO, CH3COO sind high-spin-Verbindungen mit magnetischen Momenten zwischen 5,1 und 5,3 B. M. [Fepy4F2] reagiert mit 1,10-Phenanthrolin dagegen nur unter Bildung eines vermutlich polymeren 1:1-Komplexes [FephenF2]n.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The pathology of thrombophlebitis primarily results from the obliteration of venous valves in the lower extremities. The objective of this study was to develop a prosthetic venous valve that could be implanted in the human femoral system to ameliorate the deleterious effects of thrombophlebitis. Prosthetic venous valves were produced from two materials: Pellethane valves were fabricated from a dip-casting process; umbilical vein valves were produced by a fixation process. The valves were evaluated as implants within the external jugular veins of 10 research dogs. Each animal was implanted with one Pellethane valve in one external jugular vein and one umbilical vein venous valve in the contralateral jugular vein. Each valve was positioned over a stainless-steel cylinder that had been implanted into the jugular veins in such a manner that there existed no blood-cylinder interaction. Patency of the valves was determined by X-ray venography at 24, 48, and 72 h and at 5 and 8 days postoperatively. All of the umbilical vein venous valves were occluded by the end of 48 h, whereas two of the Pellethane venous valves remained patent for at least 5 days but were occluded at 8 days. The results of this study suggest the possibility of success of Pellethane valve implants in the venous circulation and indicate future directions for study.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0935-6304
    Keywords: Gas chromatography, GC ; Glass and fused silica capillary columns ; Coating time and efficiency ; 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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  • 6
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transformation of Uridine Derivatives into Cytidines via Selective AminationThe synthesis of some 5-fluorosubstituted cytidine 2 derivatives via amination of corresponding uridine derivatives 1 is described. 5-Substituted 4-tetrazolo pyrimidinone derivatives 5 are key intermediates in the procedure. The method used is extended to other fluorinated starting materials, e.g. fluorinated uridinedinueleotides 7 or 2′-deoxy-2′-fluorouridine 9. The fluoro containing products are easily available by fluorination with elemental fluorine or hydrogene fluoride.
    Type of Medium: Electronic Resource
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