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71.
Rainer Schmidt Angelika Bieger Elena Ziegenhagen und Klaus Dose 《Fresenius' Journal of Analytical Chemistry》1981,308(2):133-136
Zusammenfassung Ein Verfahren zur quantitativen Bestimmung von T-2-Toxin in verschimmeltem Reis bzw. Mais durch Extraktion, dünnschicht-chromatographische Trennung und Fluorescenzintensitätsmessung der mit H2SO4 behandelten DC-Platte wird vorgestellt. Fluorescenzabsorptions- und Fluorescenzemissionsspektrum werden angegeben. Die Abhängigkeit der Mycotoxinkonzentration von der Fluorescenzintensität wird durch eine Gleichung beschrieben. Die analytische Detektion von T-2-Toxin läßt sich durch ein 4-(p-Nitrobenzyl)pyridin-Derivat und dessen Absorptionsspektrum bestätigen. Versuche mit zugesetztem T-2-Toxin zeigten einen Analysenfehler von weniger als 10%.
Determination of T-2-toxin in vegetable foodstuffs1. T-2-toxin in mouldy rice and maize
Summary A procedure is described for the determination of T-2 toxin in extracts from mouldy rice and maize by thin-layer chromatography (TLC) and subsequent fluorescence intensity measurement of the H2SO4-treated TLC plates. The fluorescence absorption and emission spectra are presented. The dependence of the concentration of the mycotoxin on fluorescence intensity is described by an equation. The detection of T-2 toxin can be confirmed by colour reaction with 4-(p-nitrobenzyl)pyridine yielding a blue derivative. Experiments with added toxin revealed an analytical error smaller than 10%.相似文献
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74.
H. Elias G. Gumbel S. Neitzel und H. Volz 《Fresenius' Journal of Analytical Chemistry》1981,306(4):240-244
Zusammenfassung Zur empirischen Beschreibung der Polarität binärer Lösungsmittelgemische wurden mit einem solvatochromen Betain-Farbstoff ET-Werte für folgende Systeme bestimmt: Methanol/Butanol-2, Methanol/2-Methylbutanol-2, Methanol/Pyridin, Methanol/Acetonitril, Methanol/Toluol und Ethanol/ 2,2,2-Trifluorethanol. In allen Systemen treten mehr oder weniger starke Abweichungen vom idealen Mischungsverhalten auf, was im einzelnen diskutiert wird. In den genannten Lösungsmittelgemischen wurde parallel die Kinetik der Ligandensubstitution an einem neutralen Kupfer(II)-bis-chelatkomplex vermessen. Die ET-Werte korrelieren mit den lnkWerten (k = Geschwindigkeitskonstante für den durch das Solvens induzierten Ligandenaustausch). Dies weist darauf hin, daß die Bildung des Übergangszustandes durch H-Brücken erleichtert wird.
Polarity of binary solvent mixtures: Determination of ET(30)-values and correlation with kinetic solvent effects
Summary The polarity of binary solvent mixtures is empirically described by ET-values as determined with a solvatochromic betaine dye. The following mixtures were studied: methanol/butanol-2, methanol/2-methylbutanol-2, methanol/pyridine, methanol/acetonitrile, methanol/toluene and ethanol/2,2,2-trifluoroethanol. All mixtures behave as more or less non-ideal systems which is discussed in detail. Parallel to the determination of ET-values the kinetics of ligand substitution in a neutral copper(II)-bis-chelate complex were studied in the same set of solvent mixtures. The ET-values correlate with the corresponding lnk-values (k = rate constant for solvent induced ligand substitution). This would mean that the formation of the transition state is facilitated by hydrogen bonding.
Für finanzielle Unterstützung bedanken wir uns bei der Deutschen Forschungsgemeinschaft und dem Verband der Chemischen Industrie e.V. Der verwendete Salicylaldehyd wurde uns von der Firma Bayer AG, Leverkusen, zur Verfügung gestellt. 相似文献
75.
Kreidler B Baro A Frey W Christoffers J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(9):2660-2667
Regioselective enamine formation from cyclic β‐diketones 1 is obtained by the appropriate choice of activating agent: Brønsted acid catalyzed condensation gives endocyclic enamines 3 as the thermodynamically favored products. Activation with Lewis acid BF3 ? OEt2 affords betaines 8 as intermediate products, which can be reacted with L ‐valine diethylamide ( 2 ) to preferentially furnish exocyclic enamines 4 as kinetic products. Derivatives with quaternary stereocenters were accessible from both isomeric enamines by using asymmetric, copper(II )‐catalyzed Michael reactions at ambient temperature. Both regioisomers afford the triketones 7 with the same constitution but bearing the opposite absolute configuration at the quaternary stereocenter. Thus, both enantiomers of the product are prepared by using the same chiral auxiliary derived from L ‐valine. 相似文献
76.
Brückner A 《Chemical communications (Cambridge, England)》2005,(13):1761-1763
For the first time, three operando methods, namely EPR, UV-vis and laser-Raman spectroscopy have been applied in parallel on the same V/TiO2 catalyst and under identical reaction conditions during oxidative dehydrogenation of propane to elucidate structure-reactivity relationships in status operandi. 相似文献
77.
78.
In the context of augmented Lagrangian approaches for solving semidefinite programming problems, we investigate the possibility of eliminating the positive semidefinite constraint on the dual matrix by employing a factorization. Hints on how to deal with the resulting unconstrained maximization of the augmented Lagrangian are given. We further use the approximate maximum of the augmented Lagrangian with the aim of improving the convergence rate of alternating direction augmented Lagrangian frameworks. Numerical results are reported, showing the benefits of the approach. 相似文献
79.
In this work we study properties of random graphs that are drawn uniformly at random from the class consisting of biconnected
outerplanar graphs, or equivalently dissections of large convex polygons. We obtain very sharp concentration results for the
number of vertices of any given degree, and for the number of induced copies of a given fixed graph. Our method gives similar
results for random graphs from the class of triangulations of convex polygons. 相似文献
80.
In the setting of high-dimensional linear models with Gaussian noise, we investigate the possibility of confidence statements connected to model selection. Although there exist numerous procedures for adaptive (point) estimation, the construction of adaptive confidence regions is severely limited (cf. Li in Ann Stat 17:1001–1008, 1989). The present paper sheds new light on this gap. We develop exact and adaptive confidence regions for the best approximating model in terms of risk. One of our constructions is based on a multiscale procedure and a particular coupling argument. Utilizing exponential inequalities for noncentral χ 2-distributions, we show that the risk and quadratic loss of all models within our confidence region are uniformly bounded by the minimal risk times a factor close to one. 相似文献