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91.
Zusammenfassung Wenn 14C und 35S nebeneinander in einer Probe vorliegen, so kann man sie nicht mit Hilfe der Impuls-Verteilung bestimmen, da sich ihre Spektren praktisch decken. Bei der Bestimmung von Tritium neben 14C oder 35S nach der obigen Methode ergeben sich Fehler, wenn Quenchverbindungen in variabler Menge vorhanden sind. In der vorliegenden Arbeit werden daher diese Isotope — nach Oxydation der Probe an einer Düse — getrennt. 35S wird in Form der Oxide an Silber absorbiert und nach Elution des Silbersulfats bestimmt. 3H wird als Wasser in angesäuertem Methanol absorbiert, 14C wird als CO2 in Äthanolamin-Methanol zurückgehalten. In beiden Fällen kann man das betreffende Isotop direkt in der Absorptionslösung messen.
Summary 14C together with 35S cannot be determined by puls-height analysis, because the spectra of these isotopes are almost identical. The determination of 3H accompanied by 14C or 35S is incorrect if quenching compounds of variable amount are present. This publication recommends to convert these isotopes into the corresponding oxidation products (by combustion at nozzles) followed by separation of the oxidation products. The oxides of 35S are absorbed on silver and counted after elution of silver sulphate. 3H is trapped as water in acidified methanol and 14C is retained as CO2 in ethanolamine-methanol. In both cases each isotope may be determined in the absorbant by direct liquid-scintillation counting.相似文献
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96.
Eugen Scholz 《Fresenius' Journal of Analytical Chemistry》1980,303(3):203-207
Zusammenfassung Karl Fischer-Reagentien, die SO2 und Amin im üblichen Molverhältnis 12 enthalten, können nur mit Pyridin hergestellt werden. Stark basische Amine bewirken eine rasche Zersetzung der Reagenslösung und einen instabilen Endpunkt. Erhöht man den SO2-Anteil soweit, daß das Molverhältnis SO2Amin mindestens 11 ist, geben auch stark basische Amine hervorragende KF-Reagentien. Sie zeichnen sich durch stabile Endpunkte und hohe Reaktionsgeschwindigkeit aus. Besonders vorteilhaft ist die Anwendung als Zweikomponentenreagens, da beide Komponenten absolut lagerstabil und titerkonstant sind.
Karl Fischer Reagents without pyridine
Summary Karl Fischer-Reagents containing SO2 and amine in the normally applied molar ratio of 12 can be prepared only by using pyridine. Strong basic amines lead to a rapid decomposition of the reagent solution and to an instable endpoint. By raising the SO2-content to a molar ratio SO2amine of 11, even strong basic amines can be applied yielding KF-reagents of superior quality. They are characterized by stable endpoints and a high speed of reaction. Application as a two-solution reagent gives an additional advantage, because the single components are absolutely stable for storage and the titre remains constant.相似文献
97.
The current distribution is investigated theoretically in a shielded superconducting film, which is a film deposited on an insulating superconducting ground plate. An exact result is obtained in the case of a thin and wide film on the basis of London's equation. 相似文献
98.
A short review about nonassociative algebraic systems (mainly nonassociative algebras) and their physical applications is presented. We begin with some motivations, then we give a brief historical overview about the formation and development of the concept of hypercomplex number system and about some earlier applications. The main directions discussed are the octonionic, Lie-admissible, and quasigroup approaches. Also, some problems investigated in Tartu, the octonionic approach, Moufang–Mal'tsev symmetry, and associator quantization are discussed. This review does not pretend to be complete as the accent is placed on ideas and not on the techniques, also the references are quite sporadic (there are many authors and results mentioned in the text without references). 相似文献
99.
Eugen Scholz 《Fresenius' Journal of Analytical Chemistry》1988,330(8):694-697
Summary Karl Fischer titration can be applied to many phenols without any interference, though some are oxidized during titration. One-component reagents are to be preferred because they are less sensitive to interferences. Only pyrogallol and aminophenols are oxidized in this case. With two-component reagents dihydroxybenzenes and naphthols are oxidized, too. With coulometric titration interferences are more frequent. The oxidation rate depends on the pH and can be suppressed or minimised by adding salicylic acid to the Karl Fischer reagent. 相似文献
100.
Bald I Deng Z Illenberger E Huels MA 《Physical chemistry chemical physics : PCCP》2006,8(10):1215-1222
We report that 10-100 eV Ar+ ion irradiation induces severe damage to the biologically relevant sugar molecules D-ribose and 2-deoxy-D-ribose in the condensed phase on a polycrystalline Pt substrate. Ar+ ions with kinetic energies down to 15 eV induce effective decomposition of both sugar molecules, leading to the desorption of abundant cation and anion fragments, including CH3+, C2H3+, C3H3+, H3O+, CHO+, CH3O+, C2H3O+, H-, O-, and OH-, etc. Use of isotopically labelled molecules (5- 13C D-ribose and 1-D D-ribose) reveals the site specificity for some of the fragment origins, and thus the nature of the chemical bond breaking. It is found that all of the chemical bonds in both molecules are vulnerable to ion impact at energies down to 15 eV, particularly both the endo- and exocyclic C-O bonds. In addition to molecular fragmentation, several chemical reactions are also observed. A small amount of O-/O fragments abstract hydrogen to form OH-. It is found that the formation of the H3O+ ion is related to the hydroxyl groups of the sugar molecules, and is associated with additional hydrogen loss from the parent or adjacent molecules via hydrogen abstraction or proton transfer. The formation of several other cation fragments also requires hydrogen abstraction from its parent or an adjacent molecule. These fragmentations and reactions are likely to occur in a real biomedium during ionizing radiation treatment of tumors and thus bear significant radiobiological relevance. 相似文献