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981.
Summary In this work we establish the basic layout of IONICS, an expert system for optimizing the separation of ionogenic solutes in Reversed-Phase Liquid Chromatography, using the pH and the organic-modifier concentration of the mobile phase as parameters. We also present REMO, a front-end system that automates the retention modelling stage, based on a 9-parameter model. This system uses a scale transformation to suppress several numerical problems previously observed and features a strategy for automatic calculation of an initial approximation to the model optimum. The successful application of this system to a set of seven drugs is described. The final models are accurate and have smaller numerical problems. We also describe the use of a genetic algorithm instead of classical non-linear least-squares for fitting the model to the experimental data. Results indicate that genetic algorithms are a valuable, complementary tool for retention modelling. 相似文献
982.
通过用NH4NO3溶液处理商业硅胶,制备了不同pH值的硅胶载体和一系列Co/SiO2催化剂,并考察了催化剂的还原性能.结果表明,载体pH值的降低,使Co/SiO2催化剂在工业还原条件(673K)下的还原度从30.9%提高到72.4%.用TPR和EXAFS技术研究了Co/SiO2催化剂的还原过程.结果表明,催化剂较高的还原度是由于减弱了还原过程中生成的CoO与载体硅胶之间的相互作用,从而促进了CoO的进一步还原.用FT-IR技术研究了不同pH值硅胶表面硅醇基的存在状态,发现酸性较强的载体上易于发生表面硅醇基间的缩合作用.根据实验结果提出了Co/SiO2催化剂的还原机理. 相似文献
983.
Using 2.5-dinitrophenol as an optical indicator, the pKa of cacodylic acid were spectrophotometrically determined at elevated temperatures under saturation vapor pressures. The result
is pKa = -26.41 + 1296/T + 4.973 InT whereT is in Kelvin. In a similar way, the pKa ofp-nitrophenol were obtained up to 200‡C giving pKa = -24.82 + 2135/T + 4.353 InT From these results, several thermodynamic functions of cacodylic acid andp- nitrophenol were calculated. 相似文献
984.
Glycerol is an important and valuable chemical that can be produced from renewable resources by fermentation. The desirable
features of a successful process are high values of substrate conversions and high yields and concentrations of glycerol in
the product broth, coupled with rapid fermentation cycles. Of the various osmophilic and nonosmophilic yeasts tested for their
ability to produce glycerol in the presence and absence of steering agents (sodium sulfite or sodium carbonate), an osmophilic
yeastPichia farinosa (ATCC 20210) was found to give attractive yields. Important variables influencing glycerol production by this strain under
alkaline conditions using sodium carbonate have been investigated. A rapid fermentation (less than 120 h), coupled with high
glycerol yields (45%), has been obtained. 相似文献
985.
Gawlik BM Lamberty A Pauwels J Muntau H 《Analytical and bioanalytical chemistry》2004,378(5):1284-1287
The recent proposal of thematic strategy for soil protection by the European Commission outlines that knowledge of problems associated with soil has increased considerably based on surveys, monitoring systems and data networks. Although this information is very useful, its value for the policy-making process is limited due to a lack of comparability. From this unsatisfying situation the need arises to develop an EU-wide monitoring system accompanied by suitable matrix reference materials. Experiences gained from the development and certification of IRMM-443 (The EUROSOILS) show how to approach the complex problem of providing suitable (i.e. representative) soil CRMs for the arising analytical needs to support existing and upcoming EU legislation.This paper presents briefly the quantitative findings of a certification exercise (adsorption coefficients for atrazine, lindane and 2,4-D, as well as pH in suspension). A comparison of these results with those of an intercomparison exercise organised in 1989 by the German UBA on very similar soils shows the significant improvement in the determination of soil adsorption coefficients that was induced by the EUROSOIL project. Indicative values of total and organic carbon content and nitrogen according to ISO Standards are also presented.Furthermore, the idea of reference soils and derived reference materials (for analytical purposes) as well as reference matrices (substrates for ecotoxicological testing) is highlighted and set into the context of horizontal standardisation of methods. 相似文献
986.
A chemically modified electrode (CME) for use as a potentiometric pH sensor was constructed by electropolymerizing a poly(4,4′-diaminobiphenyl) coating on a platinum electrode. The resulting CME gave a linear response to pH in the range 1–12 with a slope of ?56 mV pH?1. The CME functioned well in titration experiments and in pH measurements. No significant interference of a coexisting redox couple with the pH measurements was observed. The mechanism of the pH response of the CME is considered. 相似文献
987.
Jing Cao Hai Li Lin Pei Jie Xia Zhan Jun He 《中国化学快报》2007,18(12):1521-1524
AgSt/AgC1 composite gains were prepared by adding chloride ions to a mixed solvent in which silver stearate (AgSt) grains were dispersed under the condition of controlled pH value and characterized by SEM, XRD, UV and DSC. The results showed that AgSt/AgC1 composite grains were composed of plateqike AgSt grains with small face-centered cubic AgC1 particles formed on the surface of AgSt. UV spectra displayed a red shift of absorption for AgSt/AgC1 relative to pure AgSt or AgC1. DSC showed a new thermal phase transition of AgSt/AgC1 grains. 相似文献
988.
989.
990.
Deeb Marji Khamis Abbas Muath Atmeh 《Journal of inclusion phenomena and macrocyclic chemistry》1998,31(1):17-26
The effect of benzo-15-crown-5,15-crown-5 and 12-crown-4 on the oxidation of triethylamine by aqueous ferricyanide ion has been studied at pH 4, 7 and 11. The crown ethers retard the normal oxidation process at all pH values, the effect depending on the crown ether concentration. The three crown ethers show the same retardation effect at pH 4 and 7, while at pH 11 the retardation decreases in the order B15C5 > 12C4 > 15C5. 相似文献