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11.
12.
We describe the syntheses of 6, 8-di-tert-butyl-, 7, 9-di-tert-butyl., 6,7-di-n-propyl and 8, 9-di-n-propyl-O-spirodienonelactone from 3, 5-di-tert-butylcatechol and 3, 4-di-n-propylcatechol. 相似文献
13.
The membrane formation of crystalline poly(ethylene-co-vinyl alcohol) (EVAL), poly(vinylidene fluoride) (PVDF), and polyamide (Nylon-66) membranes prepared by dry-cast process was studied. Membrane morphologies from crystalline polymers were found to be strongly dependent on the evaporation temperature. At low temperatures, all the casting solution evaporated into a particulate morphology that was governed by the polymer crystallization mechanism. The rise in the evaporation temperature changed EVAL membrane structure from a particulate to a dense morphology. However, as the temperature increased PVDF and Nylon-66 membranes still exhibited particulate morphologies. The membrane structures obtained were discussed in terms of the characteristics of polymer crystallization in the casting solution theoretically. At elevated temperatures the crystallization was restricted for the EVAL membrane because the increase rate in the polymer concentration was fast relative to the time necessary for growth of nuclei. Nonetheless, the time available for PVDF and Nylon-66 with stronger crystalline properties was large enough to form the crystallization-controlled particulate structure that differed in particle size only. In addition, particles in the PVDF membrane were driven together to disappear the boundary, but those in the Nylon-66 membrane exhibited features of linear grain boundary. The difference in particle morphology was attributed to the Nylon-66 with the most strongly crystalline property. Therefore, the kinetic difference in the crystallization rate of the polymer solution play an important role in dominating the membrane structure by dry-cast process. 相似文献
14.
Eleven human hair samples were taken from the Chinese residents of Hong Kong for the study of hair trace elemental level and
environmental exposures. Absolute neutron activation analysis and Ge(Li) gamma-ray spectrometry were applied in the determination
of the trace elemental level. All results are reported in parts per million except for sulfur and oxygen which are reported
in percent. The trace element content of hair from a drug addict was found to be considerably different from other sampled
people. Comparison of the normal concentrations of the trace elements of the Chinese residents of Hong Kong was made with
those from people of various other national, socio-cultural and environmental backgrounds. It was found that together with
a few other trace elements, Ni, Sr, Zr and Hg content of the Chinese Residents of Hong Kong show a higher level than those
of the other sampled people. 相似文献
15.
The addition of sulfur and silver to Rh/SiO2 inhibits hydrogenation of C2H4, but promotes CO insertion and extends the linearity of Arrhenius curves for CO insertion above 543 K.
Rh/SiO2 C2H4, CO CO 543 .相似文献
16.
Nichkova M Park EK Koivunen ME Kamita SG Gee SJ Chuang J Emon JM Hammock BD 《Talanta》2004,63(5):1213-1223
Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are considered highly toxic contaminants and the environmental and biological monitoring of these compounds is of great concern. Immunoassays may be used as screening methods to satisfy the growing demand for rapid and low cost analysis. In this work, we describe the application of an immunoassay that uses 2,3,7-trichloro-8-methyldibenzo-p-dioxin (TMDD) as a surrogate standard for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to sediment and human serum samples. Sample extraction and preparation methods were developed with the aim to establish the simplest, cost-effective and efficient removal of the matrix interferences in the enzyme-linked immunosorbent assay (ELISA). The overall method for sediments is based on a hexane extraction; clean up by a multilayered silica gel column and an activated carbon column; an organic solvent exchange with DMSO–Triton X-100 and ELISA measurement. The gas chromatography–high resolution mass spectrometry (GC–HRMS) validation studies (n = 13) revealed that the method is suitable for the toxic equivalents (TEQ) screening of dioxin in sediments with a method detection limit of about 100 pg g−1 dry sediment with a precision of 13–33% R.S.D. The analysis of a large number of samples originating from different sources would be required to establish more precisely the screening level, as well as the number of false positives and negatives of dioxin TEQ by the immunoassay for sediments. The immunoassay method for sediment analysis offers improvement in speed, sample throughput, and cost in comparison to GC–HRMS. Dioxins were determined in serum samples after a simple liquid–liquid extraction and solvent exchange into DMSO–Triton X-100 without further dilution. The current method (approximate method LOQ of 200 pg ml−1 serum) is not sufficiently sensitive for the determination of dioxins in serum to measure acceptable exposure limit. 相似文献
17.
A study on the free radical cyclization reaction of substituted 1,6-dienes mediated by p-toluenesulfonyl chloride is described. 相似文献
18.
Ni/SiO2 exhibits higher activity for CO dissociation than coprecipitated Na–Mn–Ni, which is a higher oxygenate synthesis catalyst at 303 K, while Na–Mn–Ni exhibited higher CO dissociation activities at 673 K. 相似文献
19.
A sulfonyl-radical-induced addition-cyclization reaction of 1,6-dienes with p-toluenesulfonyl cyanide giving functionalized cyclopentane systems is described. 相似文献
20.