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961.
Zhen‐Ting Du Guo‐Ren Yue An‐Pai Li Jun‐Ying Ma Tong‐Xing Wu Xue‐Gong She Xin‐Fu Pan 《中国化学会会志》2004,51(3):505-508
A facile total synthesis of (±)‐nimbiol 1 has been achieved. In order to decrease the dioxo byproduct 2a , an improved oxidation system of CrO3/H2O/HOAc/NaOAc was used. 相似文献
962.
An amperometric detector with a small thin mercury film electrode is described. The device demonstrates advantageous operational
characteristics such as small dispersion (D<2) and “memory effect” (me<0.6%), extensive maximum sample frequency (msf −200
samples/h), and high sensitivity. It has been proven useful in flow-injection analysis at a constant potential under hydrodynamic
conditions. 相似文献
963.
In the course of investigations on equestrian supplemental products for the presence of doping substances, two products were found to contain forbidden substances. As reported earlier a plant extract (Mexican cactus extract) named “Energy 5” contained the anabolic androgenic steroids (AAS) stanozolol, 17β-hydroxy-17α-methyl-5α-androstane-3β-ol (3β,5α-THMT) as well as mestanolone not declared on the label. In the present study, a product called “Super Kalm Paste” was tested. Analysis by gas chromatography - mass spectrometry (GC-MS) revealed that the preparation contained the class I anti-arrhythmics quinine (trade names KinidinTM, Durules) and cinchonine. The samples were prepared according to a sample preparation procedure established for anabolic steroids in nutritional supplements for humans. The sample treatment comprised the extraction and purification of the analytes as well as the chemical conversion with N-methyl-N-trimethylsilyl-trifluoracetamide (MSTFA) to yield the trimethylsilyl (TMS)-derivatives. To verify whether the administration of such products could lead to positive doping tests, a pilot excretion study on “Energy 5” was conducted with two geldings, and urine samples were collected. Gas chromatography - high resolution mass spectrometry (GC-HRMS) after solid phase extraction and mixed derivatisation has demonstrated the presence of the stanozolol metabolite 16β-hydroxy-stanozolol in urine samples after “Energy 5” application. 相似文献
964.
EstimationoflocaldensityofsolventaboutthesoluteSolvatochromicbehaviorsofspectroscopicprobesarewidelyusedtoestimatethesol-ventstrengthofsupercriticalfluids(SCF,).i-3lnthiswork,thesolvatochrondcshiftofthen-n*transitionbandforacetone(O.o37mo1.L-')insupercrihcal(SC)CO2wasde-terminedbyUVspectroscopytostUdythesolvationeffect.TheMcRae-BaylissexpressionbasedonthedielectriccontinUUInmodelgivestherelahonshipbetWeenso1vatochromicshiftandpo1arizabilityofnonPolarsolvents4-5asfollows:wherevisthewave… 相似文献
965.
Dusanka Ž. Obadović Anikó Vajda Maya Garić A. Bubnov Vera Hamplová M. Kašpar Katalin Fodor-Csorba 《Journal of Thermal Analysis and Calorimetry》2005,80(2):519-523
Summary Thermal properties of a homologous series of ferroelectric liquid crystals S-(-)-[4-(2-n-alkoxy-propionyloxy)]biphenyl-4'-[n-alkoxy-(3,5-dimethyl)]benzoate have been investigated by polarizing optical microscopy and differential scanning calorimetry.
The mesophases were identified and confirmed by X-ray too. Three binary mixtures were prepared from the individual homologues.
In one of the mixtures (Mix1), the ferroelectric SmC* phase has broadened and became enantiotropic. This mesophase remained
monotropic in the other two mixtures (Mix2, Mix3). The chiral nematic N* phase did not appear in Mix1, but remained monotropic
for the other two mixtures. Two molecular parameters, the layer spacing and the average intermolecular distance have been
calculated from the X-ray results for the homologues and their mixtures. An intercalated tail-to-tail packing of molecules
was found both in the single compounds and their mixtures resulting in the layer spacing about half of the molecular length
of the single compounds. 相似文献
966.
Miniaturizing all dimensions of apparatus, such as electronics and computers, is the current trend followed by scientists
in various fields. The idea of Lab-on-a-Chip has significantly expanded and found its broad applications in analytical chemistry.
Microplasmas can act as a sample excitation source and are the miniaturized versions of full-sized plasmas. These can be created
in various forms, such as direct current, microwave induced, capacitively coupled and inductively coupled plasmas. Scaling
down the size would reduce the amount of gases, liquids and consumables required, as well as the sample analysis time, which
in turn would decrease the operating costs. Therefore, several research groups are involved in the development of microplasmas
for utilisation in analytical instruments. 相似文献
967.
磷酸三丁酯萃取原子吸收光谱法测定微量Cr(Ⅲ)和Cr(Ⅵ) 总被引:2,自引:0,他引:2
常用的 APDC-MIBK 和 DDTC-MIBK 萃取原子吸收法一般只能测至十几个ppb 浓度的铬,且需在较高温度下进行萃取.本文报道一种用磷酸三丁酯(TBP)萃取原子吸收光谱法测定微量 Cr(Ⅲ)和 Cr(Ⅵ)的方法.实验表明,Cr_2O_7在盐酸介质中可与 TBP 形成 Cr(Ⅵ)-TBP-Cl-溶剂化合物,借此可测定0-0.25μg·ml~(-1)浓度范围内的 Cr(Ⅵ).若用 KMnO_4将平行试样中的 Cr(Ⅲ)氧化为 Cr(Ⅵ),测得总铬量,通过差减法即可算出Cr(Ⅲ)的含量.本法灵敏度高,准确度好. 相似文献
968.
运用HREELS技术对甲醇在预吸附氯的Ag(111)表面上的吸附氧化行为进行了较细致的研究.结果证明Cl对甲醇氧化的影响缘于它在Ag(111)上的吸附所引起的表面结构的改变进而改变表面氧吸附物种,从而使得甲醇氧化的中间产物发生变化.实验结果说明甲醇在Ag(111)和低暴露量氯吸附的Ag(111)表面上的氧化行为是相似的,检测到了中间产物Ⅰ和Ⅲ;在高暴露量氯吸附的Ag(111)上甲醇氧化时则产生中间产物Ⅰ、Ⅳ和甲醛物种.对上述不同的甲醇氧化行为作了分析,并指出了以前人们在考察甲醇氧化机理时只考虑原子氧作用的片面性. 相似文献
969.
Zhaoyang Cheng Shipei Xing Jun Guo Biao Cheng Lan‐Fang Hu Xing‐Hong Zhang Zhan Lu 《中国化学》2019,37(5):421-421
The cover picture shows that sequential 1,1‐dihydrosilylation of terminal aliphatic alkynes with primary silanes enabled by one earth‐abundant cobalt catalyst has been developed. This protocol is operationally simple using readily available aliphatic alkynes, including simple acetylene and complex drug derivative, for efficient access to valuable gem‐bis(dihydrosilyl)alkanes in highly regioselective and atom‐economic manners. Corresponding asymmetric transformations are achieved with excellent enantioselectivities. More details are discussed in the article by Lu et al. on page 457–461.
970.