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41.
Vilar RB da Silva R Schossler P Cataluña Veses R Piatnicki C Samios D Caramão EB 《Journal of chromatography. A》2003,985(1-2):367-373
This work reports preliminary studies on the characterisation of anhydrous ethanol (AEA) used as an automotive fuel mixed with gasoline in Porto Alegre (South Brazil). Pre-concentration of the impurities contained in 1000 ml of AEA was carried on through solid-phase extraction using XAD4 resin. The main compounds in the extract were identified by means of spectral data from the library of the equipment. The concentrate was then fractionated using a preparative liquid chromatographic column filled with activated silica gel and the elution procedure was carried out with, n-hexane, n-hexane-benzene (1:1, v/v) and dichloromethane. Prior to analysis by GC-MS, each fraction was reduced to 1 ml with a gentle stream of nitrogen. Saturated linear hydrocarbons and aromatic hydrocarbons eluted in the first fraction and oxygenated compounds such as aldehydes. ketones and alcohols, eluted in the second one. were the main compounds detected in the sample. 相似文献
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A fluorescence method involving sample pre-treatment is investigated concerning the determination of cefoxitin. A fluorescent product is formed when samples containing cefoxitin are subjected to alkaline hydrolysis with 1.0M sodium hydroxide and heated for 60 min at 90 degrees . The fluorescence is measured in ethanol/water medium (50% v/v) at approximately pH 2.0 provided by adding of 0.1M hydrochloric acid. The fluorescence excitation and emission maxima were 317 and 400 nm, respectively. The quantitative range is between 0.020 and 1.40 mug/ml. A detection limit of 2 x 10(-3) mug/ml was found. The proposed method has been applied to the determination of cefoxitin in commercial injections, saline and glucosed physiological serum. 相似文献
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A comparative electrochemical study of 2,4-dinitrophenol (DNP), albumin and DNP-albumin has been carried out at a hanging mercury drop electrode, in order to use DNP as a universal label in immunoelectrical assays. Several electrochemical techniques have been used. Differential pulse voltammetry has proved to be the most suitable. Wide dynamic linear ranges (more than three orders of magnitude for DNP-albumin) and low detection limits have been achieved (5 x 10(-10)M, 2 x 10(-10)M, 3 x 10(-12)M for DNP, albumin and DNP-albumin, respectively). Good reproducibility has been obtained in all cases (R.S.D. < 2.2%). 相似文献
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The synthesis of tetracyclic polyhydroxyquinones 5a and 5b was achieved through a sequence involving two Diels-Alder reactions with 1-methoxy-1,3-cyclohexadiene: the first with 2-(p-tolylthio)naphthazarin and the second on the resulting tricyclic derivative previously transformed into a (p-tolylsulfinyl)naphthazarin. The success of this strategy stemmed from the efficient remote regiocontrol exerted by the thioether substituent in the first step. 相似文献
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