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101.
Introduction Ionchromatography (IC)hasbeenrecognizedasausefulmethodfortheseparationofinorganicanionsandcationssinceitsintroductionbySmalletal .in 1975 .1AsignificanttrendinthedevelopmentofICmethodissearchforsensitiveanduniversaldetectionmethods .Themaindet… 相似文献
102.
A method based on headspace solid-phase microextraction-gas chromatography-mass spectrometry is proposed for the quality control of multilayer packaging and its manufacturing process. Volatile organic compounds (VOCs) are produced in the manufacturing process of the packaging. They can cause organoleptic problems or modify the properties of the packaging depending on the nature and the amount of the VOCs formed. The quantification using packaging samples with a known VOC concentration for the calibration is proposed in order to reduce the analysis time, and the method is validated using a statistical test. Finally, the method is applied to the determination of odour-responsible compounds in multilayer packaging samples obtained under different extrusion-coating conditions, i.e. type of extruder, type of polymer and extrusion speed. 相似文献
103.
A novel thin-layer amperometric detector (TLAD) based on chemically modified ring-disc electrode and its application for simultaneous measurements of nitric oxide (NO) and nitrite (NO2−) in rat brain were demonstrated in this work. The ring-disc electrode was simultaneously sensitive to nitric oxide (NO) and nitrite (NO2−) by modifying its inner disc with electropolymerized film of cobalt(II) tetraaminophthalocyanine (polyCoTAPc)/Nafion and its outer ring with poly(vinylpyridine) (PVP), respectively. The ring-disc electrode was used to constitute a novel TLAD in radial flow cell for simultaneous measurements of NO and NO2− in rat brain combined with techniques of high performance liquid chromatography (HPLC) and in vivo microdialysis. It was found that the basal concentration of NO in the caudate nucleus of rat brain is lower than 1.0×10−7 mol l−1, NO2− concentration is 5.0×10−7 mol l−1 and NO exists in brain maybe mainly in the form of its decomposed product. 相似文献
104.
A copper-catalyzed three-component reaction of alkenes, cycloketone oximes and DABCO·(SO2)2 is developed, which provides a convenient route for the synthesis of diverse(E)-cyanoalkylsulfonyl alkenes in moderate to good yields with excellent regio-and stereoselectivity. A broad substrate scope with excellent functional group tolerance is observed. A plausible radical pathway is proposed, which involves copper-catalyzed ring-opening C–C bond cleavage of O-acyl oxime and inser... 相似文献
105.
Cyanobenzaldehydes (m-,o-,p-) were synthesized by oxidation of corresponding tolunitriles with molecular oxygen,catalyzed by cobalt acetate and sodium bromide. 相似文献
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108.
《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,272(1-2):48-55
The macromolecular structure of humic substances (HS), i.e. molecular size, shape, conformation, and weight is believed to control key physico-chemical reactions in aquatic systems. However, these properties of HS are still deeply a matter of debate. Furthermore, they are affected by solution physico-chemical parameters such as ionic strength, pH, and chemical composition, etc. To better understand aggregation processes of HS in natural waters, the effects of cation concentration and type, water composition, and pH on the size and conformation of the Suwannee River Humic Acid (SRHA) were investigated with synthetic solutions. The size and the conformation of the SRHA in NaCl and CaCl2 solutions at different concentrations (0.001–0.5 M) and pH (4.5–9.3) were determined using the photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM), respectively. In addition, dissolved organic matter (DOM) samples collected from the Adour estuary along a salinity gradient were imaged by TEM. The average size of the SRHA measured by PCS increased with pH and ionic strength. This behavior was confirmed by TEM micrographs. The increase in pH and CaCl2 engendered aggregation of the SRHA. Two aggregation steps were identified, a big increase in HS size occurred for small changes in CaCl2 concentrations in the range <0.02 M CaCl2, and a slight increase occured for higher concentrations in the range >0.02 M CaCl2. The parallel analysis of SRHA by PCS and TEM allowed overcoming the limits for both techniques.Comparable results were found for the DOM samples from the Adour estuary (South West of France). The conformation and size of the HS network of these samples varied with the salinity gradient. TEM images demonstrated that, HS have a branched open network in freshwater whereas they have a more compacted and close network with increasing salinity. 相似文献
109.
Zhuxing Tang Yun Zhou Yikun Zeng Shuliang Zang Pingang He Yuzhi Fang 《Chromatographia》2006,63(11-12):617-622
A method based on capillary electrophoresis with electrochemical detection has been developed for the separation and determination of epicatechin, isovanillic acid, vanillic acid and myricetin in Dioscorea bulbifera L. and its medicinal preparations. The effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time were investigated. Under optimum conditions, the analytes could be separated in a 40 mmol L?1 borate buffer (pH 8.7) within 15 min. A 300 μm diameter carbon disk electrode has a good response at + 0.95 V (vs. SCE) for all analytes. The response was linear over three orders of magnitude with detection limits (S/N = 3) ranging from 3.0 × 10?8 g mL?1 to 1.0 × 10?7 g mL?1. The method has been successfully applied to the analysis of real samples. 相似文献
110.
研究了在三种固体超强酸催化下醛(酮)自身的羟醛缩合反应,系统考察了反应时间,催化剂用量等因素对反应的影响,优化了反应条件.同时,对该反应的溶剂效应进行了研究.结果表明,当催化剂用量为2 g/1 mol醛(酮),反应5 h,转化率可达40%,溶剂对该反应有明显的抑制作用.超强酸对各种醛都具有较好的催化活性,其催化醛类化合物自身缩合的转化率都在48%以上,选择性在95%以上,证明固体超强酸对该缩合反应有较好的催化活性和选择性. 相似文献