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排序方式: 共有209条查询结果,搜索用时 31 毫秒
121.
122.
Marc Hostettler Dieter Schwarzenbach Vladimir Dmitriev 《Solid State Communications》2004,129(6):359-363
Angle dispersive X-ray diffraction experiments on mercuric bromide (HgBr2) under high pressure up to 11.0 GPa were carried out at room temperature using synchrotron radiation. In addition to the already known four different phases of HgBr2 in the pressure-temperature range of p<4.5 GPa, 90<T<600 K our observations show the existence of a new phase (V) above 9.0 GPa and, together with published material, support the phase transition sequence: (I) orthorhombic-(II) orthorhombic-(III) monoclinic-(IV) trigonal-(V) trigonal/hexagonal. The structure of phase IV with space group symmetry P3 has been determined from powder diffraction data. The observation of second-harmonic-generation signals confirms the absence of an inversion center. The structure of phase IV is a commensurately modulated variant of the CdI2 type layer structure, where part of the Hg atoms are displaced from the centers of the HgBr6 octahedra by a much as 0.76 Å in the direction perpendicular to the layers. 相似文献
123.
Quantification of estrogenic mycotoxins at the ng/L level in aqueous environmental samples using deuterated internal standards 总被引:2,自引:0,他引:2
Hartmann N Erbs M Wettstein FE Schwarzenbach RP Bucheli TD 《Journal of chromatography. A》2007,1138(1-2):132-140
Because of their pronounced estrogenicity, resorcyclic acid lactones (RALs) are of concern in aqueous environments even at the low ng/L level. Therefore, we developed an accurate, precise and sensitive HPLC-MS/MS method to detect these mycotoxins in different aqueous environmental samples. The compounds investigated included zearalenone (ZON), alpha- and beta-zearalenol, zearalanone as well as alpha- and beta-zearalanol. The use of isotope labelled internal standards (in this case deuterated RAL-analogues) ensured an accurate quantification of the target analytes, independent of matrix compounds interfering with the analytes during ionisation and analyte losses occurring during sample preparation. Sample enrichment was carried out by solid-phase extraction (SPE) using Supelclean Envi-18 cartridges. Absolute method recoveries for all analytes ranged from 95 to 108%, 70 to 102%, and 76 to 109%, method detection limits from 0.5 to 2.1 ng/L, 0.4 to 1.1 ng/L, and 0.8 to 12.4 ng/L and precision from 3 to 14%, 2 to 13% and 4 to 16% in drainage water, river water and wastewater treatment plant (WWTP) effluent, respectively. The method was applied to verify the emission of RALs from a Fusarium graminearum infested crop field into the drainage system. Zearalenone was present in drainage water in concentrations up to 30 ng/L. So far, none of the other five investigated compounds have been detected. 相似文献
124.
Han CY Willing GA Xiao Z Wang HH 《Langmuir : the ACS journal of surfaces and colloids》2007,23(3):1564-1568
In this work, it has been shown that, through a highly controlled process, the chemical etching of the anodic aluminum oxide membrane barrier layer can be performed in such a way as to achieve nanometer-scale control of the pore opening. As the barrier layer is etched away, subtle differences revealed through AFM phase imaging in the alumina composition in the barrier layer give rise to a unique pattern of hexagonal walls surrounding each of the barrier layer domes. These nanostructures observed in both topography and phase images can be understood as differences in the oxalate anion contaminated alumina versus pure alumina. This information bears significant implication for catalysis, template synthesis, and chemical sensing applications. From the pore opening etching studies, the etching rate of the barrier layer (1.3 nm/min) is higher than that of the inner cell wall (0.93 nm/min), both of which are higher than the etching rate of pure alumina layer (0.5-0.17 nm/min). The established etching rates together with the etching temperature allow one to control the pore diameter systematically from 10 to 95 nm. 相似文献
125.
Gerold Schick Michael Raab Dietrich Gudat Martin Nieger Edgar Niecke 《Angewandte Chemie (International ed. in English)》1998,37(17):2390-2392
The first oligomeric phosphazene in which each phosphorus center features a PH functionality ( 3 ) was obtained from the amidophosphane 1 or its zirconium complex 2 . 相似文献
126.
Aeppli C Berg M Hofstetter TB Kipfer R Schwarzenbach RP 《Journal of chromatography. A》2008,1181(1-2):116-124
A direct aqueous injection-gas chromatography/mass spectrometry (DAI-GC/MS) method for trace analysis of 24 volatile organic compounds (VOCs) in water samples is presented. The method allows for the simultaneous quantification of benzene, toluene, ethyl benzene, and xylenes (BTEX), methyl tert-butyl ether (MTBE), tert-butyl alcohol (TBA), as well as a variety of chlorinated methanes, ethanes, propane, enthenes and benzenes. Applying a liquid film polyethylene glycol or a porous layer open tubular (PLOT) divinylbenzene GC capillary column to separate the water from the VOCs, volumes of 1-10 microL aqueous sample are directly injected into the GC. No enrichment or pretreatment steps are required and sample volumes as low as 100 microL are sufficient for accurate quantification. Method detection limits determined in natural groundwater samples were between 0.07 and 2.8 microg/L and instrument detection limits of <5 pg were achieved for 21 out of the 24 evaluated VOCs. DAI-GC/MS offers both good accuracy and precision (relative standard deviations 相似文献
127.
128.
129.
Stefan W. Toennes Moritz G. Wagner Gerold F. Kauert 《Analytical and bioanalytical chemistry》2010,398(2):769-777
Acetaldehyde adducts of hemoglobin have been regarded as potential biochemical markers of alcohol exposure. In this study
a novel sensitive method using liquid chromatography coupled to time-of-flight mass spectrometry (LC–TOF MS) has been used
to investigate changes in adduct levels in alcohol detoxification patients. Hemoglobin and authentic blood samples from 66
adults with an alcohol-dependence syndrome and from 12 children were analyzed for acetaldehyde modifications with and without
trypsin digestion using LC–TOF MS. After in-vitro incubation of hemoglobin with increasing concentrations of acetaldehyde,
followed by tryptic digestion, 21 modified peptide fragments could be identified from their accurate mass and retention time
shift. Eight of these could also be detected in authentic human blood samples. Trace amounts in children’s blood were indicative
of an endogenous source. Modified peptide levels in patients’ samples with and without ethanol were significantly different,
as also were levels in samples from admission and from five days later. Samples obtained 5, 10, or 15 days after admission
did not differ in adduct levels. The LC–TOF MS method was sensitive enough to detect acetaldehyde-modified hemoglobin peptides
in blood samples from patients with an alcohol-dependence syndrome. However, elevated levels were only observed after recent
ethanol consumption and decreased during five days of abstinence, suggesting that acetaldehyde-modified tryptic peptides of
hemoglobin are potential biomarkers only for short-term ethanol ingestion. 相似文献
130.
Laura Isac Gerold Thoelking Albrecht Schwab Hans Oberleithner Christoph Riethmuller 《Analytical and bioanalytical chemistry》2011,399(7):2351-2358
A demanding task of medicine is to understand and control the immune system. Central players in the cellular immune response
are the leukocytes that leave the blood stream for host defense. Endothelial cells limit the emigration rate of leukocytes.
Being located between blood and tissues, they permit or deny the passage. The exact mechanism of this process called diapedesis
is not solved yet. Leukocytes can principally traverse either between cells (paracellularly) or directly through an individual
endothelial cell (transcellularly). The transcellular way has recently gained experimental support, but it is not clear how
the endothelial cytoskeleton manages to open and close a transmigratory channel. Atomic force microscopy was used to investigate
the endothelial cytoskeleton. In order to directly access the leukocyte–endothelial interaction site, we applied a special
protocol (“nanosurgery”). As a result, the endothelial cell turned out to become softer in a confined region strictly underneath
the leukocyte. Fluorescence microscopy confirmed a depolymerization of the f-actin strands at the invasion site. Leukocytes
dramatically rearrange the endothelial cytoskeleton to form transmigratory channels. 相似文献