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991.
A simple and sensitive method for the determination of liquid methanol and ethanol at trace levels by an alkyl nitrite formation reaction has been established. Alcohol was allowed to react with nitrous acid, which was yielded from sulfuric acid and sodium nitrite in the solution, to form the corresponding alkyl nitrite in the hexane organic phase. Alkyl nitrites in hexane were analyzed by a gas chromatograph with an electron capture detector (GC-ECD). The detection limits, which were determined at a signal-to-noise ratio of 3, were 1.1 and 0.7 micrograms/L for methanol and ethanol, respectively, by 1 microL injection. The relative standard deviations for n = 8 were 4.0 and 3.3% for methanol and ethanol, respectively. The method was applied to determine the alcohol concentration in a rice paddy, pond water, tap water, and well water. Those aqueous samples were also spiked with standard alcohols; the average recoveries of spiked methanol and ethanol were 98 and 91% with relative standard deviations of 6.1 and 4.0%, respectively. 相似文献
992.
993.
994.
Two-dimensional, shell-cross-linked nanoparticle arrays. 总被引:2,自引:0,他引:2
Q Ma E E Remsen T Kowalewski K L Wooley 《Journal of the American Chemical Society》2001,123(19):4627-4628
995.
Summary An on-line flow injection-solid-phase extraction-capillary zone electrophoresis (FI-SPE-CZE) method has been developed for
determination of cimetidine in human plasma. Sodium dodecylsulfate (SDS) was used as dynamic chemical modifier for elimination
of capillary contamination by biological macromolecules. FI on-line preconcentration and cleaning of the analyte by means
of a C18 microcolumn was performed automatically and CZE separation was performed consecutively without interruption of the applied
voltage and between-run-washing of the capillary. A detection limit of 8 μgL−1 (3×σ) was achieved at a sample throughput of 12h−1. The approach was successfully used for a pharmacokinetic study of cimetidine. 相似文献
996.
Air-side heat transfer and friction characteristics of five kinds of fin-and-tube heat exchangers, with the number of tube rows (N = 12) and the diameter of tubes (Do = 18 mm), have been experimentally investigated. The test samples consist of five types of fin configurations: crimped spiral fin, plain fin, slit fin, fin with delta-wing longitudinal vortex generators (VGs) and mixed fin with front 6-row vortex-generator fin and rear 6-row slit fin. The heat transfer and friction factor correlations for different types of heat exchangers were obtained with the Reynolds numbers ranging from 4000 to 10000. It was found that crimped spiral fin provides higher heat transfer and pressure drop than the other four fins. The air-side performance of heat exchangers with the above five fins has been evaluated under three sets of criteria and it was shown that the heat exchanger with mixed fin (front vortex-generator fin and rear slit fin) has better performance than that with fin with delta-wing vortex generators, and the slit fin offers best heat transfer performance at high Reynolds numbers. Based on the correlations of numerical data, Genetic Algorithm optimization was carried out, and the optimization results indicated that the increase of VG attack angle or length, or decrease of VG height may enhance the performance of vortex-generator fin. The heat transfer performances for optimized vortex-generator fin and slit fin at hand have been compared with numerical method. 相似文献
997.
Characteristics of mass spectra of isomeric tetradecadien-1-ols were investigated by electron impact mass spectrometry, and mass spectral fragmentation pathways were proposed based on collision-induced dissociation experiments and mass-analyzed ion kinetic energy spectrometry. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
998.
999.
D. Raghavan X. Gu T. Nguyen M. Vanlandingham 《Journal of Polymer Science.Polymer Physics》2001,39(13):1460-1470
Characterization of polymer coatings microstructure is critical to the fundamental understanding of the corrosion of coated metals. An approach for mapping the chemical heterogeneity of a polymer system using chemical modification and tapping‐mode atomic force microscopy (TMAFM) is demonstrated. This approach is based on the selective degradation of one of the phases in a multiphase polymer blend system and the ability of TMAFM to provide nanoscale lateral information about the different phases in the polymer system. Films made of a 70:30 polyethyl acrylate/polystyrene (PEA/PS) blend were exposed to a hydrolytic acidic environment and analyzed using TMAFM. Pits were observed to form in the PEA/PS blend films, and this degradation behavior was similar to that of the PEA material. Using these results, the domains in the 70:30 blend were identified as the PS‐rich regions and the matrix as the PEA‐rich region. This conclusion was confirmed by Fourier transform infrared‐attenuated total reflection analyses that revealed the hydrolysis of the PEA material. TMAFM phase imaging was also used to follow pit growth of the blend as a function of exposure time. The usefulness of the chemical modification/AFM imaging approach in understanding the degradation process of a coating film is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1460–1470, 2001 相似文献
1000.