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991.
In the present paper, we describe a microfluidics-based sensing system for nonelectroactive anions under negative separation electric field by mounting a single carbon fiber disk working electrode (WE) in the end part of a poly(dimethylsiloxane) microchannel. In contrast to work in a positive separation electric field described in our previous paper (Anal. Chem. 2004, 76, 6902-6907), here the electrochemical reduction reaction at the WE is not coupled with the separation high-voltage (HV) system, whereas the electrochemical oxidation reaction at the WE is coupled with the separation HV system. The electroactive indicator is the carbon fiber WE itself but not dissolved oxygen. This provides a convenient and sensitive means for the determination of nonelectroactive anions by amperometry. The influences of separation voltage, detection potential, and the distance between the WE and the separation channel outlet on the response of the detector have been investigated. The present detection mode is successfully used to electrochemically detect F-, Cl-, SO4(2-), CH3COO-, H2PO4-. Based on the preliminary results, a detection limit of 2 microM and a dynamic range up to three orders of magnitude for Cl- could be achieved. 相似文献
992.
TEM investigation of formation mechanism of monocrystal-thick b-oriented pure silica zeolite MFI film 总被引:3,自引:0,他引:3
Li S Li Z Bozhilov KN Chen Z Yan Y 《Journal of the American Chemical Society》2004,126(34):10732-10737
The first direct transmission electron microscopic (TEM) observation has been carried out on the continuous monocrystal-thick b-oriented pure silica zeolite MFI films produced by in situ crystallization. The self-supporting film samples for TEM study were fabricated by dissolving the steel substrate with acid. This TEM study is free of those artifacts that are typically associated with TEM sample preparations, and allows us to investigate the "true" structure and texture of a very large area of the film and at the same time to focus at will on each individual zeolite crystal in the film. Abundant TEM information including crystallographic orientation relationships among crystals in the film (both out-of-plane and in-plane), grain boundaries, and each crystal grain was obtained. This TEM investigation provides direct unambiguous new evidence to support the homogeneous nucleation mechanism, by which the films form through homogeneous nucleation and crystal growth in the bulk to form equal-sized disk-shape crystals, followed by self-assembly of these crystals onto the substrate to produce a two-dimensional close-packed structure. The last stage of the film formation involves simultaneous space-limited growth and rotation of the individual crystals to realize the in-plane crystallographic control within the film. 相似文献
993.
The adsorption equilibrium isotherms of three aromatic sulfonic acid compounds, 2-naphthalenesulfonic acid, p-toluenesulfonic acid and p-chlorobenzenesulfonic acid, from aqueous solutions by macroporous weak base anion exchanger within the temperature range of 293 K-313 K were obtained. Several isotherm equations were correlated with the equilibrium data, and the experimental data was found to fit the three-parameter Redlich-Peterson equation best within the entire range of concentrations. The study showed that the hydrophobicity of solute has distinct influence on adsorption capacity of the anion exchanger for the aromatic sulfonic acid. Moreover, estimations of the isosteric enthalpy, free energy,and entropy change of adsorption were also reported. The positive isosteric enthalpy and entropy change for adsorption indicate an endothermic and entropy driven process in the present study. 相似文献
994.
本文评述了表面热电离质谱(TIMS),特别是负离子质谱(NTI-MS)对非金属和具有高电离电位的金属元素的同位素测定的进展,引用文献34篇。 相似文献
995.
用循环伏安法研究了[Mo_3OCl_6(O_2CR)_3]-(其中R=CH_3,H,CH_2Cl)系列三核钼簇合物在CH_3CN和DMF溶剂中的电化学行为,并用差热-热重手段研究了它们的热稳定性和热分解过程的可能机理。结果表明在不同溶剂中它们有相似的二对氧化还原峰,而且在同一溶剂中随着R基团吸电子能力的增强,相应的第一氧化还原电位值向正向移动。当R=CH_3,H时,它们的起始分解温度分别为265℃和210℃,即同样随着R基团吸电子能力的增强,起始分解温度降低。 相似文献
996.
用超临界流体干燥法制备出大孔高比表面高分散态Fe/ZrO_2气凝胶超细粒子催化剂,研究了在其制备过程中织构性质、颗粒大小、体相和表面结构的变化,并与普通浸渍法制备的Fe/ZrO_2催化剂作了对比。对几种Fe/ZrO_2催化剂的F-T反应性能考察表明,Fe/ZeO_2气凝胶超细催化剂显示出高的反应活性;随载体ZrO_2颗粒尺寸减小,活性组分铁的分散度变大,其颗粒尺寸变小,催化剂比表面积增大,反应活性增大,甲烷和低碳烃生成量增加,重质组分减少,认为产物烃分布主要受催化剂活性相颗粒尺寸效应制约。 相似文献
997.
998.
A series of Fe-P-B ultrafine amorphous alloy particles has been prepared by the chemical reduction method The composition and size of the particles have been effectively adjusted.Mossbauer spectroscopy in addition to sonic other techniques has been used to investigate the reaction process,the factors that influence the preparation,the crystallization of the particles,and the interactions between the components within them.The results indicate that the co-deposition of iron,phosphorus and boron atoms in the solution at room temperature forms Fe-P-B amorphous alloy particles,and a preferential bonding of Fe-P bond to Fe-B one exists in the particles. 相似文献
999.
本文论述了WO_3薄膜氢离子敏器件的结构、原理、制备技术和测试分析。利用WO_3薄膜在H+溶液中由绝缘转化为导电特性,成功地研制成氢离子敏器件。这是一种简易而经济的微型pH敏器件技术。 相似文献
1000.
Rearrangement with formamide extrusion in the electrospray mass spectra of aminoacylbenzylamines 总被引:1,自引:0,他引:1
Chen J Jiang Y Fu H Chen Y Cheng C Zhao Y 《Rapid communications in mass spectrometry : RCM》2001,15(16):1489-1493
Several aminoacylbenzylamines and their analogs were synthesized and analyzed by electrospray ionization mass spectrometry together with high-resolution and tandem mass spectrometric techniques. Fragment ions ([M + H - CH3NO](+)) were observed and attributed to a transfer of the benzyl group to the N-terminal amino group, leading to elimination of formamide. The proposed mechanism is supported by accurate mass measurements, and by experiments on deuterium labeling and variations of functional groups. 相似文献