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171.
172.
Klaus Kaiser Hugo Obermann Gerd Remberg Margot Spiteller-Friedmann Gerhard Spiteller 《Monatshefte für Chemie / Chemical Monthly》1970,101(1):240-263
Zusammenfassung Die Kombination eines Gaschromatographen mit einem hochauflösenden Massenspektrometer kann bei der Untersuchung von Steroidgemischen, die aus biologischen Materialien isoliert wurden, rasche Information über sonst kaum nachweisbare Steroidmetaboliten liefern. Die Erfassungsgrenze liegt bei etwa1 .Freie Steroide zeigen strukturspezifischere Spektren als ihre Trimethylsilylderivate, so daß, wenn immer möglich, auf eine Silylierung zur gaschromatographischen Trennung verzichtet werden sollte. Ist wegen der Schwerflüchtigkeit der Verbindung eine Derivatbildung notwendig, so ist die Umwandlung von Hydroxysteroiden in entsprechende Ketosteroide in den meisten Fällen einer Trimethylsilylierung vorzuziehen.Umsetzungen können im Gemisch ausgeführt werden, so daß zumindest eine teilweise Strukturaufkläurung ohne Reinisolielierung der Probe mit Mengen von 10 bis 20 möglich ist.
Mit 14 Abbildungen
Herrn Prof. Dr.F. Kuffner zum 65. Geburtstag gewidmet. 相似文献
Possibilities and limitations of using a direct combination of gas chromatograph—high resolution mass spectrometer in the study of naturally occurring steroids
The combination of a gaschromatograph with a high resolution mass spectrometer may provide in the investigation of steroids, isolated from natural sources, fast information about otherwise barely detectable minor steroid metabolites. The limit of detection is about 1 .Free steroids show more structure specific spectra than their corresponding trimethylsilyl derivatives. Therefore the preparation of trimethylsilyl derivatives for the purpose of gaschromatographic separation should be avoided if possible. If low volatility necessitates the preparation of a derivative, in most cases the preparation of keto derivatives from hydroxysteroids should be preferred to the preparation of trimethylsilyl ethers.Reactions can be carried out with the mixture, so that-without preparation of pure samples-at least partial structure determinations are possible with 10–20 .
Mit 14 Abbildungen
Herrn Prof. Dr.F. Kuffner zum 65. Geburtstag gewidmet. 相似文献
173.
Hugo J.H. Schielke 《European Journal of Operational Research》1981,6(3):258-268
A new practical method for buying and selling decisions of bond investments which has been applied successfully by the World Bank for three years. 相似文献
174.
V. Hugo Schmidt 《Solid State Communications》1980,35(9):649-652
Dielectric susceptibility and ferroelectric hysteresis measurements on TSCC show that the 2nd-order paraelectric-ferroelectric (PE-FE) phase boundary beginning at (130.8 K, 1 bar) runs with pronounced curvature to (176.8 K, 5.03 kbar), where a new phase of low dielectric susceptibility appears. This phase is hypothesized to be antiferroelectric (AFE) with 3 possible structures: orthorhombic (P212121, piezoelectric) or monoclinic ( or , centrosymmetric). The FE-AFE phase boundary was determined down to (81.0 K, 2.60 kbar) and the PE-AFE boundary up to (225.5 K, 6.82 kbar). Both the FE-AFE and PE-AFE transitions are of 1st order over the range studied. 相似文献
175.
Hugo Volger 《Mathematische Zeitschrift》1968,106(4):312-320
Ohne Zusammenfassung 相似文献
176.
Lauri J. Missio Hugo S. Braibante Mara E. F. Braibante 《Journal of heterocyclic chemistry》1996,33(4):1243-1245
The reactivity of the enamino compounds 4-amino-3-phenylamino(thio)carbonyl-3-penten-2-one 1 and 2 and ethyl 3-amino-2-phenylamino(thio)carbonyl-2-butyrate 7 and 8 was studied using the reaction with hydrazine hydrate and hydrazine hydrochloride to evaluate the 1,3 electrophilic center of the compounds by the formation of the pyrazole rings. The pyrazoles 3, 4, 5, 9, 11 and 13 were obtained depending on the reaction conditions employed. 相似文献
177.
Hugo M. Ortner Gerhard Schlemmer Bernhard Welz W. Wegscheider 《Spectrochimica Acta Part B: Atomic Spectroscopy》1985,40(7):959-977
Morphological studies on graphite tube surfaces by scanning electron microscopy are presented for unused and corroded tubes from various endurance experiments in electrothermal AAS.Tubes always break in their center as this is the hottest part; tube thinning occurs predominantly at the outside. The inner surface of tubes coated with pyrographite is usually only slightly corroded, unless highly aggressive reagents are applied. Deposition of carbon in thin layers as well as in nodules is observed in the hot central zone. 相似文献
178.
Benjamin Braun Hugo Corrales Scott Corry Luis David García Puente Darren Glass Nathan Kaplan Jeremy L. Martin Gregg Musiker Carlos E. Valencia 《Discrete Mathematics》2018,341(10):2949-2963
Let be a finite, connected graph. An arithmetical structure on is a pair of positive integer vectors such that , where is the adjacency matrix of . We investigate the combinatorics of arithmetical structures on path and cycle graphs, as well as the associated critical groups (the torsion part of the cokernels of the matrices ). For paths, we prove that arithmetical structures are enumerated by the Catalan numbers, and we obtain refined enumeration results related to ballot sequences. For cycles, we prove that arithmetical structures are enumerated by the binomial coefficients , and we obtain refined enumeration results related to multisets. In addition, we determine the critical groups for all arithmetical structures on paths and cycles. 相似文献
179.
We deal with anomalous diffusions induced by continuous time random walks - CTRW in ?n. A particle moves in ?n in such a way that the probability density function u(·, t) of finding it in region Ω of ?n is given by ∫Ωu(x, t)dx. The dynamics of the diffusion is provided by a space time probability density J(x, t) compactly supported in {t ≥ 0}. For t large enough, u satisfies the equation , where δ is the Dirac delta in space-time. We give a sense to a Cauchy type problem for a given initial density distribution f. We use Banach fixed point method to solve it and prove that under parabolic rescaling of J, the equation tends weakly to the heat equation and that for particular kernels J, the solutions tend to the corresponding temperatures when the scaling parameter approaches 0.
相似文献
$$u\left( {x,t} \right) = \left[ {\left( {J - \delta } \right)*u} \right]\left( {x,t} \right)$$
180.