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101.
A simple method is described for the speciation of metalions in biological extracts with a short desalting gel-filtration column. The system was optimized for the eluent and gel type to provide accurate free metal ion levels and minimum processing times. The four separation media studied were Sephadex G25, Bio-Gel P-6DG, controlled pore glass CPG40, and Fractogel HW40F. The best medium was the Fractogel HW40F because it was not compressible and allowed a pump to be used to obtain uniform flow rates. The eluent was 0.10 M ammonium acetate/0.01 M citric acid adjusted to pH 7.0. This eluent minimized ion/gel interactions and gave a lower salt content relative to other possible eluents. The separation time was 10 min per sample per metal ion of interest. The detection limits relative to the mass of wet tissue for the column/flame spectrometer system were 0.80 μg g?1, 0.80 μg g?1, and 1.6 μg g?1 for zinc, cadmium and copper, respectively. The method is evaluated for a lobster digestive gland extract; the methodology should be applicable to other systems containing nonlabile metal species. 相似文献
102.
Siham El FangourAlexandre Guy Jean-Pierre VidalJean-Claude Rossi Thierry Durand 《Tetrahedron letters》2003,44(10):2105-2108
The first synthesis of the two enantiomers of phytoprostane F1 methyl ester 1 and 2 is described using the syn-anti-syn alcoxy ester 3 as starting material. 相似文献
103.
Focant JF Eppe G Scippo ML Massart AC Pirard C Maghuin-Rogister G De Pauw E 《Journal of chromatography. A》2005,1086(1-2):45-60
A comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC x GC-TOF-MS) experimental setup was tested for the measurement of seven 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs), ten 2,3,7,8-substituted polychlorinated dibenzofurans (PCDFs), four non-ortho-polychlorinated biphenyls (PCBs), eight mono-ortho-PCBs, and six indicator PCBs (Aroclor 1260) in foodstuff samples. A 40m RTX-500 (0.18mm I.D., 0.10 microm df) was used as the first dimension (1D) and a 1.5 m BPX-50 (0.10mm I.D., 0.10 microm df) as the second dimension (2D). The GC x GC chromatographic separation was completed in 45 min. Quantification was performed using 13C-label isotope dilution (ID). Isotope ratios of the selected quantification ions were checked against theoretical values prior to peak assignment and quantification. The dynamic working range spanned three orders of magnitude. The lowest detectable amount of 2,3,7,8-TCDD was 0.2 pg. Fish, pork, and milk samples were considered. On a congener basis, the GC x GC-ID-TOF-MS method was compared to the reference GC-ID high resolution mass spectrometry (HRMS) method and to the alternative GC-ID tandem-in-time quadrupole ion storage mass spectrometry (QIST-MS/MS). PCB levels ranged from low picogram (pg) to low nanogram (ng) per gram of sample and data compared very well between the different methods. For all matrices, PCDD/Fs were at a low pg level (0.05-3 pg) on a fresh weight basis. Although congener profiles were accurately described, RSDs of GC x GC-ID-TOF-MS and GC-QIST-MS/MS were much higher than for GC-ID-HRMS, especially for low level pork and milk. On a toxic equivalent (TEQ) basis, all methods, including the dioxin-responsive chemically activated luciferase gene expression (DR-CALUX) assay, produced similar responses. A cost comparison is also presented. 相似文献
104.
Borovkov VV Lintuluoto JM Hembury GA Sugiura M Arakawa R Inoue Y 《The Journal of organic chemistry》2003,68(19):7176-7192
The complexation behavior, binding properties, and spectral parameters of supramolecular chirality induction in the achiral host molecule, syn (face-to-face conformation) ethane-bridged bis(zinc porphyrin), upon interaction with chiral bidentate guests (diamines and amino alcohols) have been studied by means of UV-vis, CD, fluorescence, (1)H NMR, and ESI MS techniques. It was found that the guest structure plays a decisive role in the chirogenesis pathway. The majority of bidentate ligands (except those geometrically unsuitable) exhibit two major equilibria steps: the first guest ligation leading to formation of the 1:1 host-guest tweezer structure (K(1)) and the second guest molecule ligation (K(2)) forming the anti bis-ligated species (1:2). The second ligation is much weaker (K(1) > K(2)) due to the optimal geometry and stability of the 1:1 tweezer complex. The enhanced conformational stability of the tweezer complex ensures an efficient chirality transfer from the chiral guest to the achiral host, consequently inducing a remarkably high optical activity in the bis-porphyrin. 相似文献
105.
The character of transient electric fields induced in spherical homogeneous tissue models of man and animals by incident electromagnetic fields similar to that originating from lightning and EMP generators has been theoretically determined. The magnitude of the induced fields is found to be approximately proportional to the time rate of change of the incident field and independent of the pulsewidth. It was also found that maximum EMP induced field in spherical shaped bodies is nearly proportional to the radius of the body. Therefore, for EMP safety standards, more consideration should be given to the time rate of change of the incident field rather than to the pulsewidth, and when laboratory animal data are used as a guide they should be extrapolated to account for body size. 相似文献
106.
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108.
This paper deals with functional linear regression for spatial data. We study the asymptotic properties of an estimator of a linear model where a spatial scalar response variable is related to a spatial functional explanatory variable and to its derivative. Convergence results with rate of this estimator are derived. 相似文献
109.
110.
Computational Fluid Dynamic Design of Jet Stirred Reactors for Measuring Intrinsic Kinetics of Gas‐Phase and Gas‐Solid Reactions 下载免费PDF全文
Nonreactive and reactive computational fluid dynamic simulations were applied to optimize the design of a laboratory scale jet stirred reactor for measuring intrinsic kinetics of gas‐phase and gas‐solid reactions, i.e. kinetics determined by chemical steps only and not by heat or mass transfer. In the past these reactors were designed and tested based on empirical design criteria and residence time distribution experiments. This work shows that these do not always capture important local effects that are vital for kinetic studies. First the degree of macro–mixing was evaluated for three different geometries (down case, 45° case and 90° case) by performing in silico residence time distribution experiments at 900 K, showing that with these type of experiments only minor differences are observed. However, the ethane steam cracking simulations revealed major differences, with the 45° case being the most uniform in terms of temperature and the 90° case being by far the worst. The species nonuniformity in all geometries was acceptable and was in some cases even partly masked by important shortcut streams such as those observed in the 90° case. The existing gradients on the substrate surface are sufficiently small to be neglected in modeling efforts. As temperature is the major parameter determining the rate of the surface reactions, the 45° case is suggested as the best geometry for measuring intrinsic kinetics. 相似文献