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231.
232.
A rapid and sensitive analytical method has been developed for trace analysis of methyl tert‐butyl ether (MTBE) in water samples using dispersive liquid‐liquid microextraction and gas chromatography with flame ionization detection. Factors relevant to the microextraction efficiency, such as the kind of extraction solvent, the disperser solvent and their volumes, the effect of salt, sample solution temperature and the extraction time were investigated and optimized. Under the optimal conditions the linear dynamic range of MTBE was from 0.2 to 25.0 μg L?1 with a correlation coefficient of 0.9981 and a detection limit of 0.1 μg L?1. The relative standard deviation (RSD%) was less than 5.1% (n = 3) and the recovery values were in the range of 97.8 ± 0.9%. Finally, the proposed method was successfully applied for the analysis of MTBE in aqueous samples. 相似文献
233.
The resonance scattering theory (RST) is applied to the problem of sound scattering from an elastic transversely isotropic
solid sphere suspended in an ideal acoustic fluid medium. The normal mode expansion technique in conjunction with the Frobenius
power series solution method is utilized to deal with the material anisotropy. The presented model, which degenerates to the
simple isotropic solution in the case of very weak anisotropy, is initially employed to study sensitivity of various resonant
modes of vibration to perturbations in elements of the stiffness matrix. Employing a rigid background subtraction, the target’s
spectrum of resonances is extracted from the relevant modal backscattering form functions and subsequently traced and discussed
through Regge pole trajectory plots. Also, the backscattering form function and resonance spectra, along with the dispersion
curves for selected transversely isotropic solid spheres with distinct degrees of material anisotropy, are calculated and
discussed. The various modes of propagation associated with the Rayleigh, Whispering Gallery, and fluid-borne Scholte-Stoneley
surface waves are identified and examined.
Published in Russian in Akusticheskiĭ Zhurnal, 2008, Vol. 54, No. 2, pp. 205–218.
The text was submitted by the authors in English. 相似文献
234.
Electrochemical determination of 2,4-D at a mercury electrode 总被引:1,自引:0,他引:1
An indirect electrochemical determination of 2,4-dichlorophenoxyacetic acid (2,4-D), has been presented. The method is based on the adsorption and desorption of 2,4-D on mercury electrode. Also, the electrochemical behavior of 2,4-D in aqueous solutions at different pH values and different 2,4-D concentrations were studied. A simple and rapid method has been developed for its extraction from water and soil. The subsequent determination was carried out by a tensammetric method. Three calibration curves could be obtained from different parts of voltammogram. Under the optimum conditions (pH = 2.3; Eacc = −1100 mV; tacc = 60 s; alternative current mode; ν = 40 mV s−1; pulse height = 20 mV; modulation frequency = 60 Hz; phase angle = 90°) the limit of detection was 50 μg L−1. The proposed method was applied to the determination of 2,4-D in real samples such as soil and water. 相似文献
235.
Structural Chemistry - The interaction of procarbazine (PC) anticancer drug with fullerene-like nanocages (B24N24, AlB23N24, SiB23N24, B24N23Si, CB23N24) was studied by density functional theory... 相似文献
236.
A sulfonated magnetic cellulose‐based nanocomposite was prepared and characterized using scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction and Fourier transform infrared spectroscopy. Then, it was used as a green nanocatalyst for the synthesis of α‐aminonitriles by a one‐pot three‐component condensation reaction of aldehydes or ketones, amines and trimethylsilylcyanide in ethanol at room temperature. The reaction procedure is simple, yields are very high, reaction time is very short and the catalyst can be easily separated from the reaction mixture and reused in subsequent reactions without significant loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
237.
Reza Tayebee Mojtaba Fattahi Abdizadeh Nasrin Erfaninia Amirhassan Amiri Mehdi Baghayeri Roya Mohammadzadeh Kakhki Behrooz Maleki Effat Esmaili 《应用有机金属化学》2019,33(8)
Phosphotungstic acid (H3PW12O40, PTA) supported on ZIF‐9(NH2) was synthesized for the first time and performed as an effective and environmental friendly catalyst in the one‐pot three component Biginelli condensation of different substituted benzaldehydes with ethyl acetoacetate and urea to afford the corresponding 3,4‐dihydropyrimidin‐2‐(1H)‐ones under solvent‐free conditions. ZIF‐9(NH2) and the prepared nanocatalyst PTA@ZIF‐9(NH2) were characterized by XRD, FESEM, TEM, EDX, BET, AAS, TGA, UV–Vis, and FT‐IR. After reaction, the nanocatalyst can be easily separated from the reaction mixture by centrifuge and the recovered catalyst can be reused for at least five times with a 14% reduction in yield after the fifth run. This study showed that ZIF‐9(NH2) can be utilized as a promising support for PTA and developed a highly active, stable and reusable heterogeneous catalyst under easy reaction condition in the multi‐component organic synthesis. 相似文献
238.
Reza Tayebee Akbar Pejhan Hassan Ramshini Behrooz Maleki Nasrin Erfaninia Zohre Tabatabaie Effat Esmaeili 《应用有机金属化学》2018,32(1)
Uniform SiO2 nanoparticles were successfully prepared from Equisetum arvense obtained from the north‐east of Iran. Then, surface modification of the extracted nanoparticles was performed with a methanol solution of H3PW12O40 via wet impregnation method. The prepared nanocatalyst was characterized by XRD, FESEM, ICP, UV–Vis, and FT‐IR spectroscopy. The supported heterogeneous nanocatalyst was successfully applied as a Lewis/Bronsted acid catalyst in the synthesis of a series of substituted 4H–chromenes via condensation of aromatic aldehydes, malononitrile, and 4‐hydroxycoumarin under solventless conditions with fine yields in appropriately short times. 相似文献
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