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61.
Şevket Ata Mehmet Akyüz Erdal Dinç 《International journal of environmental analytical chemistry》2016,96(7):636-652
Gas chromatography–mass spectrometry (GC-MS) method and a liquid chromatography–fluorescence (LC-FL) detection method using experimental design and optimisation approach were improved for the quantitative determination of nitrite and nitrate in biological, food and environmental samples. The obtained recoveries of nitrite and nitrate ions from samples based on both GC-MS and LC-FL results ranged from 98.5% to 98.9% for nitrite and 97.9% to 98.4% for nitrate. The precision of these methods, as indicated by the relative standard deviations (RSDs), was within the range from 2.4% to 3.6% for nitrite and 2.5% to 3.8% for nitrate, respectively. The limits of detection of nitrite and nitrate ions from samples based on GC-MS and LC-FL results ranged from 0.01 to 0.14 ng L?1 for nitrite and 0.02 to 0.71 ng L?1 for nitrate, respectively. The optimised isolation procedure by central composite design was successfully applied to real samples. The results revealed that the proposed procedure combined with GC-MS and LC-FL techniques is more sensitive, reliable and selective compared to the other methods available for the precise determination of trace levels of nitrite and nitrate in biological, food and environmental samples. 相似文献
62.
Cobalt-modified nickel-zinc catalyst CuNi(Zn)Co is prepared on a copper substrate by using electrodeposition. Its catalytic efficiency for methanol oxidation is studied with cyclic voltammetry, chronoamperometry, and chronopotentiometry techniques. The surface morphology and chemical composition of catalyst are characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The oxidation kinetic parameters activation energy (Ea), active species on the surface (Γ), and rate constant (k) are determined from cyclic voltammograms which are performed at different methanol concentrations and temperatures. The results show that Ni(Zn)Co catalyst has higher catalytic activity than Ni, Co, and NiZn coatings as a composite catalyst for a promising choice of methanol electrooxidation in the alkaline medium. 相似文献
63.
An intramolecular Pauson–Khand reaction of enynes derived from homoallyl, homopropargyl, and allyl alcohols is described. 2-Heteroaryl-substituted homoallyl, homopropargyl, and allyl alcohols are easily and efficiently resolved through enzymatic resolution in high ee (91–99%) and with a known stereochemistry. Each enantiomerically enriched enyne derived from homoallyl and homopropargyl alcohols affords the conformationally most stable diastereomeric cyclopenta[c]pyran ring system as the sole product, whereas enantiomerically enriched enynes derived from allyl alcohols give a diastereomeric cis:trans mixture of the cyclopenta[c]furan ring system. 相似文献
64.
By making use of the well-known assertions in [S.S. Miller, P.T. Mocanu, Differential Subordinations, Theory and Applications, Marcel Dekker, New York-Basel, 2000] and [M. Nunokawa, On the order of strongly starlikeness of strongly convex functions, Proc. Japan Acad. Ser. A Math. Sci. 69 (7) (1993) 234–237], several useful results of certain inequalities dealing with analytic and univalent functions are obtained and then certain consequences of them are also indicated. 相似文献
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68.
Alexandru I. Şchiop 《Numerische Mathematik》1973,20(3):208-212
In this paper we establish the stability of Ritz procedure in sense of Michlin and Tucker for a class of nonlinear two-point boundary value problems which has been considered by Varga, Schultz and Ciarlet in [1]. 相似文献
69.
The title polymeric complex {[Mn(O2C(CF2)8CO2)(phen)2]H2O}n was synthesized through the reaction of 1,10-phenanthroline, perfluorosebacic acid and MnCO3 · H2O. The molecular structure was characterized by X-ray diffraction, elemental analysis, thermal gravimetry, IR and UV–Vis spectroscopy and its catalytic activity has been studied. X-ray structure analysis shows that each Mn(II) ion is octahedrally coordinated by two bidentate phenanthroline ligands and the carboxylate oxygen atoms from two symmetry related perfluorosebacate ligands, which are coordinated in cisoid positions. The structure consists of polymeric chains, with the perfluorosebacato ligand bridging the Mn(II) ions in a monodentate fashion. Crystallographic characterization shows a supramolecular structure involving hydrogen bonds, π–π and π-ring interactions. The catalytic results indicated that the complex has reasonably good activity towards the disproportionation of hydrogen peroxide into water and dioxygen in methanol and it does not exhibit saturation kinetics with the substrate. The initial reaction rates and their temperature and base dependencies were investigated by monitoring the dioxygen evolution. Kinetic studies revealed a first-order dependence on the catalyst concentration. Activation parameters have been calculated at 301 K. 相似文献
70.
The geometry, frequency, and intensity of the vibrational bands of imidazo[1,2-a]pyridine (which is abbreviated as impy) were
obtained by the density functional theory (DFT) calculations with BLYP, B3LYP, and B3PW91 functionals and 6-31G(d) basis set.
The optimized geometric bond lengths and bond angles are in good agreement with the available X-ray data. The infrared spectrum
of imidazo[1,2-a]pyridine was computed by the DFT method in order to reproduce the vibrational wavenumbers and intensities
with an accuracy, which allows reliable vibrational assignments. Total energy distribution and isotopic shifts have been calculated
in order to help for the perfect assignment of the vibrational modes. The zinc halide complexes Zn(impy)2X2 [X = Cl, Br, and I] have also been synthesized. The compounds were characterized using the elemental analysis, FT-IR spectra,
and quantum chemical calculations. The geometry optimization of Zn(impy)2X2 yields distorted tetrahedral environment around Zn ion. 相似文献