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41.
In the determination of free and combined chlorine, the reaction of permanganate standards with N,N-diethyl-p-phenylenediamine (DPD) exhibits nonlinearity presumably because both the colored semiquinoid product and the colorless quinoid product are both formed. The titrimetric DPD method titrates both of the products while the colorimetric method monitors only the colored semiquinoid products. This results in a nonlinear response for the colorimetric method above 1.0 mg/l. as Cl(2). Under FIA conditions, the nonlinearity of the DPD colorimetric method is eliminated in the 0.1-5.0 mg/l. (as Cl(2)) range and the linear range is expanded to 0.1-8.0 mg/l. as Cl(2). Also, relative standard deviations are improved by 0.5-11% relative to the colorimetric method and 1.5-4.0% relative to the titrimetric method. The FIA method was developed further to sequentially determine both free and combined chlorine, since chloramine was found to have a negligible interference in the free chlorine determination. 相似文献
42.
An improved synthesis of the anti-cancer agent DMU-212 (trans-3,4,5,4′-tetramethoxystilbene) is described. The methodology involves the use of a Pd-oxazoline catalyst as a mediator of a regio-selective (Heck) C-C bond formation reaction. A simple isolation step is then used to obtain the title material. The compound has been further characterised in the solid-state by X-ray diffraction methods. 相似文献
43.
A method was developed for determination of total dietary fiber (TDF) in foods containing resistant maltodextrin (RMD) which includes nondigestible carbohydrates that are not fully recovered as dietary fiber by conventional TDF methods such as AOAC 985.29 or 991.43. Because the average molecular weight (MW) of RMD is 2000 daltons, lower MW soluble dietary fiber components do not precipitate in 78% ethanol; therefore, RMD is not completely quantitated as dietary fiber by current AOAC methods. The accuracy and precision of the method was evaluated through an AOAC collaborative study. Ten laboratories participated and assayed 12 test portions (6 blind duplicates) containing RMD. The 6 test pairs ranged from 1.5 to 100% RMD. The method consisted of the following steps: (1) The insoluble dietary fiber (IDF) and high MW soluble dietary fiber (HMWSDF) were determined by AOAC 985.29. (2) Ion exchange resins were used to remove salts and proteins contained in the AOAC 985.29 filtrates (including ethanol and acetone). (3) The amount of low MWRMD (LMWRMD) in the filtrates were determined by liquid chromatography. (4) The TDF was calculated by summation of the IDF, HMWSDF, and LMWRMD fractions having nondigestible carbohydrates with a degree of polymerization of 3 and higher. Repeatability standard deviations (RSDr) were 1.33-7.46%, calculated by including outliers, and 1.33-6.10%, calculated by not including outliers. Reproducibility standard deviations (RSDR) were 2.48-9.39%, calculated by including outliers, and 1.79-9.39%, calculated by not including outliers. This method is recommended for adoption as Official First Action. 相似文献
44.
Edie M. Rasmussen Peter Willett Terence Wilson Gordon A. Manson George A. Wilson 《Analytica chimica acta》1990
The use of two types of parallel computer hardware for increasing the efficiency of processing in chemical structure data bases is discussed. The distributed array processor can be used for the clustering of 2-D chemical structure data bases by using the Jarvis—Patrick clustering method and for the ranking of output in an experimental system for substructure searching in the 3-D macromolecules in the Protein Data Bank. The Inmos transputer can be used in the construction of PC-based systems for 2-D substructure searching and in the identification of the maximal substructures common to pairs of 3-D molecules. 相似文献
45.
Due to the widespread uses of Ni and Ni alloys, patients undergoing medical treatments can experience inadvertent exposure to the metal, present as a contaminant in fluids for intravenous administration or released from surgical implants and other medical devices. Because of the risk of acute allergic reactions in Ni-sensitive subjects, sources of metal exposure within medical care and its concentrations in biological fluids of potentially exposed patients should be periodically monitored, using reliable analytical procedures, which include strict measures of contamination control. The results of a recent survey on the concentrations of Ni and other potentially toxic metals in human albumin solutions are reported. 相似文献
46.
Asymmetric induction was achieved in the photoaddition of 3-methyl-2-cyclohexenone to optically active enoates 1a–c and the absolute configuration of the major adduct was determined. 相似文献
47.
The effect of mixing (or “splicing”) extended and minimal basis sets on molecular properties such as geometries, Mulliken charges, dipoles, and internal rotation barriers was studied for several test molecules. The effect is gauged by comparison with full extended basis set calculations. It is found that splicing improves most properties relative to full minimal basis set calculations, and little accuracy is lost if the splicing is done in a judicious manner. 相似文献
48.
The extent of electron quasilocalization in the high density gases is greater in ethane than in methane. However, the density required for quasilocalization in methane is n/nc > 0.1, while that in ethane is n/nc > 0.4, where nc is the critical density. The mobilities in methane and ethane cross at n = 6 × 1021 molecules/cm3, in the respective fluids along their vapor/liquid coexistence curves. 相似文献
49.
William T. Speck Amy J. Behrman Pnina G. Rosenkranz Doria Gordon Herbert S. Rosenkranz 《Photochemistry and photobiology》1980,31(5):513-517
Abstract— The unfertilized oocytes and spermatozoa of the American sea urchin ( Arbacia punctulata ) were exposed to phototherapy lights in order to determine the effect of this treatment regimen on post-irradiation fertilization and embryonic development. Light treatment revealed dose-dependent abnormalities in fertilization and subsequent embryonic development. 相似文献
50.
Huang Y Triscari JM Pasa-Tolic L Anderson GA Lipton MS Smith RD Wysocki VH 《Journal of the American Chemical Society》2004,126(10):3034-3035
Analysis of fragmentation patterns from 5654 unique doubly charged tryptic peptides is obtained. Great variability of average relative abundance of bond cleavage is found between different amino acid combinations. There exist similarities as well as differences between b and y ions. Strong enhancement or suppression of cleavage gives insight into possible chemical interactions at reactive conformations formed by preferred phi-psi angles. 相似文献