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41.
42.
A new method was developed for the rapid screening and confirmation analysis of barbital, amobarbital and phenobarbital residues in pork by gas chromatography-tandem mass spectrometry (GC/MS/MS) with ion trap MSD. The residual barbiturates in pork were extracted by ultrasonic extraction, cleaned up on a multiwalled carbon nanotubes (MWCNTs) packed solid phase extraction (SPE) cartridge and applied acetone-ethyl acetate (3:7, v/v) mixture as eluting solvent and derivatized with CH3I under microwave irradiation. The methylated barbiturates were separated on a TR-5MS capillary column and detected with an ion trap mass detector. Electron impact ion source (EI) operating MS/MS mode was adopted for identification and external standard method was employed for quantification. One precursor ion m/z 169 was selected for analysis of barbital and amobarbital and m/z 232 was selected for phenobarbital. The product ions were obtained under 1.0 V excitation voltage. Good linearities (linear coefficient R > 0.99) were obtained at the range of 0.5-50 microg kg(-1). Limit of detection (LOD) of barbital was 0.2 microg kg(-1) and that of amobarbital and phenobarbital were both 0.1 microg kg(-1) (S/N > or = 3). Limit of quantification (LOQ) was 0.5 microg kg(-1) for three barbiturates (S/N > or = 10). Satisfying recoveries ranging from 75% to 96% of the three barbiturates spiked in pork were obtained, with relative standard deviations (R.S.D.) in the range of 2.1-7.8%. 相似文献
43.
Mesoporous 1,4‐phenylene‐silica nanorings were prepared using cetyltrimethylammonium bromide (CTAB) and (S)‐2‐methyl‐1‐butanol as a chiral dopant in concentrated aqueous NH3 solutions. Transmission electron microscopy images of the samples indicated that the nanorings were formed by bending nanorods 360°. With increasing the stirring speed or the (S)‐2‐methyl‐1‐butanol/CTAB molar ratio, the morphologies of mesoporous 1,4‐phenylene‐silicas changed from helical nanofibers to nanorings, and then to nano‐saddles. Circular dichroism spectra of these hybrid silicas indicated that they were chiral. 相似文献
44.
Weike Luo Jiejun Wu John Goldsmith Yanhao Du Tongjun Yu Zhijian Yang Guoyi Zhang 《Journal of Crystal Growth》2012,340(1):18-22
About 1.2 mm thick GaN bulk crystals were obtained by combining a pulsed NH3-flow modulation (PFM) method and a self-separation method of short-shutting NH3 flow when using hydride vapor phase epitaxy (HVPE). High crystal quality of bulk GaN was evaluated by X-ray rocking curves (XRC) and the full width at half maximum (FWHM) values were 110, 72 and 83 arcsec for (002), (102) and (100) reflection planes, respectively. The PFM method is proved to be effective in reducing cracks and keeping the surface smooth. And the method of short-shutting NH3 flow can lead to GaN thick layer separate from sapphire substrate when cooling from the high growth temperature. Growth and separation mechanisms were investigated. Two states were found in PFM method. With PFM method modulating between high quality state and low stress state, 300 μm thick GaN layers without cracks were obtained. Study of spontaneous separation mechanism revealed that the separation attributed to formation of voids inside the GaN layer. 相似文献
45.
The asymptotic behavior of periodic solutions to fractal nonlinear Burgers equation is considered and the initial data are allowed to be arbitrarily large.The exponential decay estimates of the solutio... 相似文献
46.
A new method for the synthesis of 1,4-dihydropyridine(1,4-DHP)calcium channel antagonists felodipme, nitrendipine and their derivatives via papain-catalyzed three-component reactions of aldehyde,methyl acetoacetate and ethyl 3-aminocrotonate was developed.Operational simplicity,mild reaction conditions and eco-friendliness are the key features of this protocol. 相似文献
47.
Zhiyang Yan Bin Sun Xun Zhang Xiaohui Zhuang Jin Yang Weike Su Can Jin 《化学:亚洲杂志》2019,14(19):3344-3349
A novel visible‐light‐driven decarboxylative coupling of alkyl N‐hydroxyphthalimide esters (NHP esters) with quinoxalin‐2(1H)‐ones has been developed. This C(sp2)?C(sp3) bond‐forming transformation exhibits excellent substrate generality with respect to both the coupling partners. Of note, a series of 3‐primary alkyl‐substituted quinoxalin‐2(1H)‐ones that were difficult to synthesize by previous methods could be obtained in moderate to excellent yields. Additionally, the mild conditions, easy availability of substrates, wide functional group tolerance and operational simplicity make this protocol practical in the synthesis of 3‐alkylated quinoxalin‐2(1H)‐ones. 相似文献
48.
基于横向效应增强型弹丸(PELE)侵彻金属薄靶板过程分析,将弹体前端在撞击作用下的变形过程分解为轴向一维压缩和径向自由膨胀两个变形阶段;依据冲击波理论,给出了弹体前端的冲击波压缩势能,由功能转化原理,给出了PELE前端外壳在靶后形成破片的最大径向飞散速度计算公式。计算结果在多种工况下均与文献的实验结果较为一致。计算结果表明:PELE靶后外壳破片的最大径向飞散速度与外壳和内芯材料的体积模量和泊松比有关,且随二者的增大而增大;PELE外壳破片的最大径向飞散速度是壳体和内芯在冲击波压缩作用下共同径向膨胀的结果,且外壳膨胀能在弹体整体膨胀能中所占比例较大,计算中应当同时考虑弹体外壳和内芯材料的横向膨胀效应对弹体破片径向飞散速度的影响。 相似文献
49.
A novel photocatalytic cross dehydrogenative coupling reaction of N-aryl glycine esters with N-substituted anilines has been developed. The reaction proceeds effectively using methylene blue as a photocatalyst under visible light irradiation without any metal, chemical oxidant or additive. A variety of α-aryl α-amino derivatives were prepared in moderate to excellent yields with a high para-regioselectivity. 相似文献
50.
首先定义并考查了一类新的函数空间,即所谓二重余法分布.在得到了一些建立在此类余法分布空间上的能量估计之后,证明了半线性严格双曲的一阶偏微分方程组的弱奇性与强奇性相互作用后将会产生透射与反射等新奇性,而且其强度不强于原弱奇性的强度. 相似文献