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991.
Daura Vega Moreno Zoraida Sosa Ferrera Jos Juan Santana Rodríguez 《Microchemical Journal》2007,87(2):139-146
Solid-phase microextraction (SPME) and solid-phase extraction (SPE) procedures were coupling with microwave-assisted micellar extraction for organochlorine pesticides residues determination in seaweed samples. They were optimized, compared and discussed.Preliminary experiments were performed in order to study experimental conditions for the extraction of pesticides from spiked seaweed samples with microwave-assisted micellar extraction (MAME) using a non-ionic surfactant (Polyoxyethylene 10 Lauryl Ether). After that, SPME and SPE were used to clean-up and preconcentrate MAME extract prior the analysis by liquid chromatography with photodiode array (PDA) detection.Excellent results were obtained for both procedures. Average pesticide recoveries between 80.5 and 104.3% for MAME-SPME and between 73.9 and 111.5% for MAME-SPE were obtained. Relative standard deviations (RSDs) were lower than 10.3% and 5.3% respectively for all recoveries tested, and LOD between 138–348 ng g− 1 for MAME-SPME and 2–38 ng g− 1 for MAME-SPE were obtained. The method was validated using Soxhlet extraction procedure.Both methods were applied to analyse target organochlorine pesticides in several seaweed samples and results were compared. These results show the great possibilities of combining MAME-SPE-HPLC-UV for the analysis of seaweed samples, improving the selectivity and sensitivity in the determination of organochlorine pesticides analysis for this kind of samples. 相似文献
992.
A number of cyclic mono- and di-ketones underwent regioselective olefination with (carbethoxyethylidene)triphenylphospharane under controlled microwave heating. The Wittig reaction of 4-substituted cyclohexanones or 1,2- and 1,4-cyclohexanediones with the ylide at 190 °C for 20 min in MeCN afforded the exocyclic olefins in >94:6 isomer ratios. On the other hand, the same reactions carried out at 230 °C for 20 min in the presence of 20 mol % DBU furnished the endocyclic olefins in >83:17 isomer ratios. The base-mediated isomerization of the exocyclic olefins into the endocyclic isomers was primarily driven by thermodynamic stability of the products and the effect of ring structures on deconjugation was examined. 相似文献
993.
Antonietta Artillo Marco De Santis Susagna Ricart Aldo Spinella 《Journal of organometallic chemistry》2007,692(6):1277-1284
Mono and disubstituted ureas react with alkynyl Fischer carbene complexes to give mono and di N,N-substituted organometallic uracil analogues. An optimization of the process using different starting metal carbene complexes and variously substituted ureas under conventional heating (with and without solvent) and microwave irradiation techniques is reported. The synthesis of the metal-carbene analog of the commercially available dimethyl uracil is reported. 相似文献
994.
潮湿空气微波放电离子形成动力学 总被引:2,自引:0,他引:2
利用微波放电电离质谱装置,通过水蒸气与空气混合气体(潮湿空气)的微波放电,同时获得了化学电离质谱探测技术中常用的三种重要母体离子H3O+、NO+和.结合潮湿空气中主要成分N2、O2以及水蒸气各自微波放电后的质谱探测结果,对潮湿空气微波放电后上述三种离子产生的动力学过程进行了分析,并给出了各种离子的形成机制.这些离子 分子反应过程在计算机模拟中得到了进一步的证实. 相似文献
995.
Furuya K. Munakata F. Matsuo K. Akimune Y. Ye J. Okada A. 《Journal of Thermal Analysis and Calorimetry》2002,69(3):873-879
An advanced silicon nitride material with high isotropic thermal conductivity (149 W m-1 K-1) has been developed. This high thermal conductivity was achieved with a process that combines high-quality seed crystals
with a suitable additive system to promote grain growth. In this process, the addition of β-Si3N4 seed crystals was found to be effective in improving thermal conductivity due to their low defect and impurity concentrations.
The seed crystals seem to work as nuclei for controlling grain growth during the sintering process. Controlling the growth
of elongated grains so that they do not interact with each other seems important for suppressing the generation of new defects
inside the grains.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
996.
Chih-Chin Chi 《Tetrahedron》2004,60(48):10869-10876
Refluxing an o-dichlorobenzene solution of 2,5-disubstituted thienosultines 10a-f with [60]fullerene for 2-24 h gave both 1:1 and 2:1 cycloadducts in 37-79% isolated yields. The reaction was highly accelerated by microwave irradiation giving comparable yields of cycloadducts. Sultines 10a-f underwent cheletropic extrusion of SO2 to form the corresponding non-Kekulé biradical intermediates 11a-f, which were subsequently trapped by [60]fullerene to form corresponding cycloadducts. The activation energy barriers (ΔGc≠) determined for the boat-to-boat inversion of these 4′,5′,6′,7′-tetrahydrobenzo[c]thieno-[5′,6′:1,2][60]fullerene adducts 12a-f were found to be in the range of 13.5-14.8 kcal/mol. Unexpectedly, one of the monoadduct 12a was found to be labile when kept in air under ambient light. Two new products 15 (a sulfine-enone) and 16 (an endione) were isolated from the decomposed 12a and were found to derive from self-sensitized singlet oxygen reaction on the 2,5-dimethylthieno moiety of 12a. 相似文献
997.
铁合金厂回收的硅微粉在不同温度下晶相结构的研究 总被引:13,自引:0,他引:13
铁合金厂冶炼过程产生的大量硅微粉烟尘, 可以作为耐火材料和窑具材料的结合剂, 活性剂和矿化剂, 可促进耐火材料固相反应和烧结, 有利于晶型的转变, 提高耐火材料的高温性能。硅微粉在高于或等于1100 ℃不析晶。1200和1300 ℃析晶规律是:首先α-石英转变为α-方石英, 然后转变为α-鳞石英。在1400~1450 ℃首先析出卡片号为290085的石英变体, 然后转变为α-方石英。 而常规转化过程是α-方石英很难形成α-鳞石英, 而且不形成290085的变体, 因此其转化规律与常规不同。在液相存在情况下, 少量α-方石英转变为α-鳞石英, 不同温度下析晶结构探讨为实际生产提供适宜的升温曲线。 相似文献
998.
999.
在原始的FDTD细线算法基础上,把带负载细导线模型分成导线、电阻和吸收三个部分,分别用不同的偏微分方程描述,使其可以处理两端带有纯电阻性负载细线电磁脉冲散射问题,进而得到电阻负载上消耗的总能量及对应的功率消耗。用该方法计算得到的结果与文献结果进行了比较,证明了该方法的有效性。最后用此方法对一种典型情况进行了计算,并对结果进行了分析。该方法是对FDTD方法中细线算法的补充和提高,经过修改也可以用于非阻性负载的情况。 相似文献
1000.