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341.
A two‐step laser desorption lamp ionization source coupled to an ion trap mass spectrometer (LDLI‐ITMS) has been constructed and characterized. The pulsed infrared (IR) output of an Nd:YAG laser (1064 nm) is directed to a target inside a chamber evacuated to ~15 Pa causing desorption of molecules from the target's surface. The desorbed molecules are ionized by a vacuum ultraviolet (VUV) lamp (filled with xenon, major wavelength at 148 nm). The resulting ions are stored and detected in a three‐dimensional quadrupole ion trap modified from a Finnigan Mat LCQ mass spectrometer operated at a pressure of ≥ 0.004 Pa. The limit of detection for desorbed coronene molecules is 1.5 pmol, which is about two orders of magnitude more sensitive than laser desorption laser ionization mass spectrometry using a fluorine excimer laser (157 nm) as the ionization source. The mass spectrum of four standard aromatic compounds (pyrene, coronene, rubrene and 1,4,8,11,15,18,22,25‐octabutoxy‐29H,31H‐phthalocyanine (OPC)) shows that parent ions dominate. By increasing the infrared laser power, this instrument is capable of detecting inorganic compounds. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
342.
Ionic‐liquid‐based surfactant‐emulsified microextraction procedure accelerated by ultrasound radiation followed by high‐performance liquid chromatography for the simultaneous determination of antidepressant and antipsychotic drugs
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In the present work, an efficient and environmental friendly method of ionic‐liquid‐based emulsified microextraction procedure accelerated by ultrasound radiation has been developed. Subsequently, its performance was compared with dispersive liquid–liquid microextraction and ultrasound‐assisted surfactant‐based emulsification microextraction methods. The optimization of experimental conditions was carried out by combination of central composite design and response surface methodology. The optimum conditions of variables were set as follows: 50 μL of 1‐hexyl‐3‐methylimidazolium hexafluorophosphate (extracting solvent), 10 min ultrasound time, and 10 min vortex time for agitating 6 mL sample solution in pH 3 in the presence of 4 mg sodium dodecyl sulfate without addition of salt and 200 μL of methanol as diluent solvent. Under these conditions, the responses are linear for doxepin and perphenazine in the range of 0.3–1000 and 5–1000 μg/L, respectively. The limits of detection were 0.1 μg/L for doxepin and 1 μg/L for perphenazine. Relative standard deviations were lower than 3.5 for the determination of both species. Finally, the method was used for the preconcentration and determination of doxepin and perphenazine in urine sample with relative recoveries in the range of 89–98%. 相似文献
343.
non-linear vibration analysis of beam used in steel structures is of particular importance in mechanical and industrial applications. To achieve a proper design of the beam structures, it is essential to realize how the beam vibrates in its transverse mode which in turn yields the natural frequency of the system. Equation of transversal vibration of hinged–hinged flexible beam subjected to constant excitation at its free end is identified as a non-linear differential equation. The quintic non-linear equation of motion is derived based on Hamilton’s principle and solved by means of an analytical technique, namely the Homotopy analysis method. To verify the soundness of the results, a comparison between analytical and numerical solutions is developed. Finally, to express the impact of the quintic nonlinearity, the non-linear responses obtained by HAM are compared with the results from usual beam theory. 相似文献
344.
U. Lommatzsch E.H. Wahl D. Aderhold T.G. Owano C.H. Kruger R.N. Zare 《Applied Physics A: Materials Science & Processing》2001,73(1):27-33
A mixture of H2 and CH4 is passed over a hot-wire tungsten filament in a diamond thin film chemical vapor deposition reactor. The resulting CH radicals
are measured in absorption using cavity ring-down spectroscopy (CRDS). The concentration of the CH radicals increases as the
filament is approached. The rotational temperature measurements indicate a large temperature discontinuity between the filament
and the CH in the gas phase. The pathways for CH production were investigated by replacing H2 by D2 in the feed gas mixture, which resulted in the exclusive production of CD. From this observation it is concluded that rapid
H/D isotope exchange dominates in the gas phase. Nonperiodic temporal oscillations in the CH concentration are observed when
a rhenium filament is used in place of a tungsten filament. The oscillations are attributed to the nonperiodic changes in
the amount of carbon at the filament surface.
Received: 21 August 2000 / Accepted: 23 August 2000 / Published online: 23 May 2001 相似文献
345.
346.
A copper/Schiff-base complex supported on amine-functionalized silica mesoporous magnetic nanoparticles was prepared as novel magnetically interphase nanoparticles and its morphology and structure were evaluated using Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, zeta potential, and a vibrating sample magnetometer. The catalytic activity of the synthesized nanoparticles was evaluated for the synthesis of thiazolidine-4-ones. 相似文献
347.
Russian Journal of General Chemistry - The synthesis of 9-aryl-1H-xanthene-1,8(2H)-dione derivatives starting from benzaldehydes or synthesized pyrazolcarbaldehydes and dimedone in the presence of... 相似文献
348.
Russian Journal of Organic Chemistry - A series of 2-aryl-2,3-dihydroquinazolin-4(1H)-ones have been synthesized in excellent yields and short reaction time by one-pot reaction of... 相似文献
349.
Nano‐Zn[2‐boromophenylsalicylaldiminemethylpyranopyrazole]Cl2 (nano‐[Zn‐2BSMP]Cl2) as a novel nanostructured Schiff base complex was prepared and characterized using several techniques. Nano‐[Zn‐2BSMP]Cl2 was used as an effective catalyst for the preparation of some pyrano[2,3‐d]pyrimidinedione derivatives by the multicomponent reaction of malononitrile, aryl aldehydes and barbituric acid derivatives. The novelty and efficiency of nano‐[Zn‐2BSMP]Cl2 as a catalyst, in comparison with some other reported catalysts, for this synthetic transformation are the main features of this work. 相似文献
350.
Chemistry of Heterocyclic Compounds - Microreview summarizes recent methods for the synthesis of pyrrolo[2,3-d]pyrimidines, published since 2015. The methods are classified as Cu-catalyzed... 相似文献