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91.
The method of hydride generation atomic fluorescence spectrometry (HG-AFS) was optimised for determination of selenium in food supplements. Due to the high and varied content of Cu, Mg and Zn in the samples, the standard addition method was found to be the most appropriate. The reliability of the method was checked by the independent method of radiochemical neutron activation analysis, and good agreement was found between the two methods. HG-AFS is simple and rapid for Se determination in food supplements based on minerals. Agreement between the selenium values found and declared was worse than 10% in 9 out of 13 supplements. Furthermore, 2 of the 14 supplements did not comply with the recommendations stated in the 27th edition of the U.S. Pharmacopoeia, which states that minerals and vitamins in food supplements should be in the range of 90 and 200% of the declared value. 相似文献
92.
B. Hlavőček J. Šestők L. Koudelka P. Mošner J. J. Mareš 《Journal of Thermal Analysis and Calorimetry》2005,80(2):271-283
Summary The forms of vibrations and displacements of particles in amorphous structures have been investigated. The particles, moving on highly non-linear amplitude, are responsible for the creation of disordered structures of amorphous bodies. The non-linear oscillators, even if 'few' in concentration, are characterized by unpredictable trajectories in phase space. The non-linear oscillators are fully developed in the liquid state above the crossover temperature Tcr and between Tcr and Tg their number decreases. Under Tg they completely disappear. The interconnection between the linear oscillators in blocks plays the most important role in the characteristic time spectra in liquid state. Using the additive properties of elements polarizibilities, the number of acoustical units in individual blocks at Tcr is estimated to be about 600 units. The diameter of blocks at Tcr was estimated to be about 1.8 nm. Even if the non-linear high amplitude motions disappear at solidification, the remnants of structural irregularity remain and the disordered structure of glass is formed. 相似文献
93.
Synthesis and fluorescent properties of some new unsymmetricbis-benzothiazolyl furans and thiophenes
L. Racane V. Tralić-Kulenović G. Karminski-Zamola L. Fišer-Jakić 《Monatshefte für Chemie / Chemical Monthly》1995,126(12):1375-1381
Summary Some newmono- andbis-benzothiazolyl compounds with furan or thiophene nuclei were synthesized by multistep reactions from the corresponding furan and thiophene aldehydes. The data obtained from emission spectra show a large influence of the benzothiazole rings on the relative quantum efficiency of the compounds under investigation.
Synthese und Fluoreszenzeigenschaften von neuen unsymmetrischenbis-Benzothiazolylfuranen und thiophenen
Zusammenfassung Einige neuebis-Benzothiazolylverbindungen mit einem Furan- bzw. Thiophenenring wurden in einer mehrstufigen Reaktion dargestellt. Die Fluoreszenzdaten der untersuchten Verbindungen zeigen einen großen Einfluß der Benzothiazolringe auf die relative Fluoreszenzquantenausbeute.相似文献
94.
Urška L. Štangar Urh Černigoj Polonca Trebše Ksenija Maver Silvia Gross 《Monatshefte für Chemie / Chemical Monthly》2006,137(5):647-655
Summary. Transparent TiO2 films with a high photodegradation activity towards an azo dye in aqueous solution were prepared by sol–gel processing. Films
on soda–lime glass supports protected with a thin silica barrier layer exhibited better crystallization and monodisperse nanoparticles,
higher absorption of light below 370 nm, and higher photocatalytic activity than those films deposited on bare glass supports
proving the detrimental effect of interdiffused sodium ions on the development of the anatase nanostructure. The effect of
substrate was more pronounced in thinner films (300 nm) than in thicker ones (1200 nm), which were achieved by adding a template
(i.e. Pluronic F127) to the sol. 相似文献
95.
Conformations of 2-methoxytetrahydropyran as a model for the six-membered ring in aldopyranosides have been calculated by the PCILO method using the algorithm of the conjugated gradient to optimize the geometry. The calculated geometry of the fourteen basic forms of 2-methoxytetrahydropyran was found to be in agreement with the available data obtained by X-ray diffraction of pyranosides. The results indicate differences in the geometry of 2-methoxytetrahydropyran resulting from the change of the axial vs. equatorial position of the methoxyl group. These changes are particularly meaningful in the values of bond angles and they are in agreement with the anomeric and exoanomeric effects. The experimentally found differences in the energies of an axial (4
C
1) and equatorial (1
C
4) conformer, G = 2.9–3.7 kJ/mol, and the dipole moment, = 1.20 ± 0.05 D (1D = 3.33 10–30mAs) agree well with the calculated values E = 3.18 kJ/mol and <> = 1.18 D which, in turn, suggest that the axial conformer is preferred over the equatorial one by a ratio a:e = 78:22. 相似文献
96.
M. Kabešová Z. Kozfšková M. Dunaj-Jurco 《Journal of Thermal Analysis and Calorimetry》1992,38(10):2273-2279
The crystal structures and thermal behaviour of [Cu(py)2(NCS)2] (at 293) and [Cu(4-Mepy)2(NCS)2] and 180 K) complexes have been compared with their different temperature behaviour. It was found that the thermal stability of coordinated thiocyanate ligands in the course of thermal decomposition depends not only on the properties of the ligand L, but it is related to the arrangement of the thiocyanatocopper chains in the crystal structures. 相似文献
97.
Djaković-Sekulić Tatjana Perišić-Janjić Nada Sârbu Costel Lozanov-Crvenković Zagorka 《平面色谱法杂志一现代薄层色谱法》2007,20(4):251-257
JPC – Journal of Planar Chromatography – Modern TLC - Reversed-phase (RP) HPTLC with aqueous ammonia-organic modifier (acetonitrile, dioxane, acetone) mobile phases has been used to... 相似文献
98.
The thermal decomposition of some M
2
I
HPO3 (M-Li, Na, K) phosphites under nitrogen atmosphere was investigated. A stepwise mechanism of thermal decomposition has been proposed.
Zusammenfassung Es wurde die thermische Zersetzung von Phosphiten M 2 I HPO3 (M-Li, Na, K) in Stickstoffatmosphere untersucht. Die Schritte des Mechanismus der thermischen Zersetzung wurden vorgeschlagen.相似文献
99.
Z. Janout S. Pospíšil M. Vobecký 《Journal of Radioanalytical and Nuclear Chemistry》1980,56(1-2):71-81
A Doppler broadening is described of the 4438 keV spectral gamma-line observed by means of a Ge(Li) detector during the deexcitation
of nuclei of12C in an inelastic scattering12C(n, n′γ)12C using an241Am−Be source as well as during the reaction9Be(α, nγ)12C taking place in the Am−Be source. The FWHM of the spectral line is equal to (90±4) keV in the latter reaction and (64±8)
keV in the former process. Experimental values agree well with theoretical ones.
Presented at the Instrumental Activation Analysis Conference, IAA 79, June 4–8, 1979, Klučenice, Czechoslovakia. 相似文献
100.
František Kopecký Božena Kopecká Pavol Kaclík 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(3-4):215-217
The solubility of nimodipine was measured in aqueous solutions of the following cyclodextrins: -cyclodextrin (-CD), hydroxypropyl--CD (HP--CD), -cyclodextrin (-CD), random substituted methyl--CD (M--CD), three hydroxypropyl--CDs (HP--CD) with mutually different average degree of substitution, and hydroxypropyl--cyclodextrin (HP--CD). From the determined linear solubility diagrams the values of the binding constant K11 of the inclusion complexes of nimodipine with the respective CDs were evaluated. The -CDs efficiently solubilized sparingly soluble nimodipine, the highest value of K11 was found for M--CD (1680 M-1), followed by -CD (550 M-1) and HP--CDs, where the higher degree of substitution lowered K11. Only slight solubilization of nimodipine was observed in the solutions of the -CDs and HP--CD. 相似文献