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991.
Mohammad Reza Almasian Chengdui Yang Zhi Xing Sichun Zhang Xinrong Zhang 《Rapid communications in mass spectrometry : RCM》2010,24(6):742-748
A new low‐temperature plasma (LTP), based on dielectric barrier discharge (DBD), has been developed as an alternative ionization source for ambient mass spectrometry. For organic samples, the source is able to produce two different fragmentation patterns which are selectable by an electrical switch. The two source modes are different only in the second electrodes: in configuration (A), bar‐plate and in configuration (B), coaxial bar–cylinder shapes are used. A disposable graphite probe is used as the first electrode, the same in both configurations, and a copper foil is used as the second electrode. The ionization source is applicable to gas and liquid samples, without any change being necessary in its design. Under optimal conditions, to take ethylbenzene as an example, a detection limit of less than 25 ng was obtained and a relative standard deviation (RSD) of 13.36% has been demonstrated for 50 ng of ethylbenzene (n = 11). We have found several interesting differences in the mass spectra of the tested volatile organic compounds (VOCs) in the two modes, which might be applicable in identification studies. We have investigated the effect of variation of the first electrode material and the second electrode length in mode B. Moreover, in this design the graphite electrode is capable of acting as a sample adsorbent, which is a new sampling method for LTP mass spectrometry (MS). This capability was investigated by adsorption of the selected VOCs onto the surface of the graphite electrode in a headspace solid‐phase microextraction (SPME) system, and direct desorption and ionization of the samples by LTPMS. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
992.
993.
Robabeh Baharfar Mohammad Javad Taghizadeh Majid Ahmadian Seyed Meysam Baghbanian 《中国化学快报》2010,21(2):175-178
<正>The addition of 2,4-dihydroxyaceto(and benzo)phenone to propiolic ester is catalyzed by triphenylphosphine or tert-butyl isocyanide to form O-vinyl aryl derivatives in fairly good yields. 相似文献
994.
995.
Mohammad A. Mottaleb 《Mikrochimica acta》1999,132(1):31-39
A reversed-phase high performance liquid chromatography (RP-HPLC) method, with acetic acid and sodium perchlorate phase modifiers,
was developed to separate a mixture of linear alkylbenzene sulphonates (LAS), containing 10 to 13 carbon atoms. The effects
of methanol-water compositions and concentrations of used modifiers were investigated and compared. The separation achieved
with 50 mg L−1 acetic acid was found satisfactory whereas a concentration of 10 g L−1 sodium perchlorate was preferred. Chromatograms obtained with UV and Fourier transform infrared (FTIR) detection showed almost
similar features and HPLC-FTIR interface spectra of LAS components exhibited excellent agreement of absorption features to
those of standard FTIR spectrum and no thermal degradation was found to occur.
Received May 20, 1998 Revision March 25, 1999. 相似文献
996.
Using Auslander’s G-dimension, we assign a numerical invariant to any group Γ. It provides a refinement of the cohomological dimension and fits well into the well-known hierarchy of dimensions assigned already to Γ. We study this dimension and show its power in reflecting the properties of the underlying group. We also discuss its connections to relative and Tate cohomology of groups. 相似文献
997.
Mehdi Kalhor Akbar Mobinikhaledi Javad Jamshidi 《Research on Chemical Intermediates》2013,39(7):3127-3133
A simple and practical procedure for synthesis of 2-arylbenzimidazoles by a one-pot condensation of o-phenylenediamine with aromatic aldehydes in the presence of a catalytic amount of M(NO3)2·6H2O (M = Mn, Fe, Co, Ni, Cu) in ethanol at room temperature is described. Major advantages of this practical procedure are use of a readily available catalyst, high yields, short reaction times, and simplicity of the reaction and workup. 相似文献
998.
Perovskite-type barium strontium titanate(BST) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol-gel route at room temperature. The prepared sol had a narrow particle size distribution of about 20 nm. X-ray diffraction(XRD) revealed that phase composition and preferable orientation growth of BST depended upon the annealing temperature. Transmission electron microscope(TEM) images showed that the crystallite size of the powders decreased w... 相似文献
999.
Mohammad Rahimizadeh Tahmineh Bazazan Ali Shiri Mehdi Bakavoli Hassan Hassani 《中国化学快报》2011,22(4):435-438
Preyssler-type heteropoly acid is introduced as a new,mild and efficient catalyst for protection of a variety of carbonyl compounds with 1,3-propane dithiol. 相似文献
1000.