Semiautomatic and automatic amperometry and constant-current potentiometry were used to follow the course of catalytic titration of gold(III) with potassium iodide. The Ce(IV)-As(III) system in the presence of sulfuric acid was used as the indicator reaction. The possibilities of the application of two types of graphite electrodes were investigated. The effect of concentration of the indicator reaction components, and the presence of organic solvents and acids on the shape of the catalytic titration curves was studied. Amounts of 80–900 μg of gold(III) were determined with a relative standard deviation less than 1.1%. The results obtained are in good agreement with those of comparable methods. 相似文献
In the theory of iterative methods, the classical Stein-Rosenberg theorem can be viewed as giving the simultaneous convergence (or divergence) of the extrapolated Jacobi (JOR) matrix Jω and the successive overrelaxation (SOR) matrix , in the case when the Jacobi matrix J1 is nonnegative. As has been established recently by Buoni and Varga, necessary and sufficient conditions for the simultaneous convergence (or divergence) of Jω and have been established which do not depend on the assumption that J1 is nonnegative. Our aim here is to extend these results to the singular case, using the notion of semiconvergence. In particular, for a real singular matrix A with nonpositive off-diagonal entries, we find conditions (Theorem 3.4) which imply that Jω and simultaneously semiconverge for all ω in the real interval [0,1). 相似文献
A new methodology based on pressurized liquid extraction (PLE) followed by LC-MS is presented for the simultaneous and unequivocal determination of alkylphenol ethoxylates (APEOs) and their degradation products, alkylphenols (APs) and alkylphenoxy carboxylates (APECs), in sediment samples. The protocol, applicable to a full range of APEO oligomers and degradation products, permits the sensitive and selective determination of APEOs (nEO = 1-15), APECs (nEO = 0-1) and APs at low ppb levels (LODs = 1-5 microg/kg) in sediment samples. Optimization of the operational parameters of PLE clearly demonstrates that significant thermal losses of APs occur during extraction at elevated temperatures. The loss of octylphenol (OP) at 100 degrees C was 61.2% and of nonylphenol (NP) 40.0%, whereas other compounds were completely recovered. Thus, to avoid losses due to the volatility of alkylphenols, a low extraction temperature should be applied. The conditions that gave the best results for all target compounds were as follows: extraction solvent mixture, methanol-acetone (1:1, v/v); temperature, 50 degrees C; pressure, 1500 p.s.i.; two static cycles. Using PLE and a subsequent clean-up with solid-phase extraction (SPE), the simultaneous extraction of APEOs, APs and APECs from sediment samples was achieved yielding recoveries >70% and producing low MS background noise. The developed methodology was applied on a routine basis to the analysis of alkylphenolic compounds in sediment samples. APEOs and their persistent degradation products were detected in significant concentrations in sediments from Portuguese rivers, especially at sites situated in the proximity of industrial plants (mainly the textile industry). The total concentration of alkylphenolic compounds (APEOs+APs+APECs) ranged from 155 to 2400 microg/kg. Of all the alkylphenolic compounds, NP comprised 40 to 50% with concentrations up to 1172 microg/kg. 相似文献
iPP/sPP, iPP/rPP, iPP/PVDF and iPP/PA-6 blends, and their β-nucleated forms were prepared in the present study. The components of iPP/sPP and iPP/rPP blends are compatible in the molten state. The phase structure of the melt of iPP/PVDF and iPP/PA-6 blends is heterogeneous. The melting and crystallisation characteristics as well as the structure and polymorphic composition of these blends were studied by polarised light microscopy (PLM) and differential scanning calorimetry (DSC). When semicrystalline polymers are added to iPP, the most important factor of the formation a blend with β-crystalline phase is the α-nucleation effect of the second polymer. In the case of polymers with an α-nucleating effect, the temperature range of their crystallisation should be lower than that of β-iPP. β-nucleated iPP/PVDF and iPP/PA-6 blends are extreme examples showing that completely β-iPP matrix can not form even in the presence of a highly effective β-nucleant, because of the strong α-nucleating ability and higher crystallisation temperature range of PVDF and PA-6. We found that the β-crystallisation tendency of random propylene copolymers can be enhanced by adding an iPP homopolymer. 相似文献
The paper reports on the measurements of magnetic susceptibility of methylalcohol and toluene adsorbed on polypropylenes of two different molecular masses PP 5056, PP 5078, polyethylene-terephtalate and cellulose. The measurements were carried out for the full range of covering, possible at room temperature, and comparison with the additivity law was made in the whole range of concentrations. With the exception of methylalcohol in PP 5078, all samples showed noticeable deviations from linearity in the dependence of susceptibility on the percentual share of the adsorbate, the deviations were towards decreasing diamagnetism. Polyethyleneterephtalate with methylalcohol showed contradictory results. The measurements were completed with a magnetic study of adsorption of natural air and pure oxygen on cellulose and PP 5506.As far as the interpretation is concerned, the measurements of magnetic susceptibility are in good agreement with experiments on high resolution nuclear magnetic resonance (NMR). From the experimental results the authors draw up conclusions as to the character of mutual interaction of polymers with given adsorbates, to the location of an adsorbed molecule on the polymer surface, and to the contribution of Van Vleck polarization paramagnetism and other susceptibility components on the experimental results.Toluene C6H5.CH3, adsorbed on polypropylene, showed two more peaks beside a NMR signal of C6H5; they were identified as the signals of CH3 adsorbed on non-equivalent parts of a polypropylene macromolecule. 相似文献
In several real networks large heterogeneity of links is present either in intensity or in the nature of relationships. Therefore, recent studies in network science indicate that more detailed topological information are available if weighted or multi-layer aspect is applied. In the age of globalization air transportation is a representative example of huge complex infrastructure systems, which has been analyzed from different points of view. In this paper a novel approach is applied to study the airport network as a weighted multiplex taking into account the fact that the rules and fashion of domestic and international flights differ. Restricting study to only topological features and their correlations in the system (disregarding traffic) one can see reasons why simple network approximation is not adequate. 相似文献
The reliability of measurement results is essential for forming a common database of a laboratory network, because a well-maintained and consistent database is the crucial point of countrywide monitoring. Reference materials are important tools in realizing some aspects of quality assurance; they are especially useful in harmonizing work within the network. Among usual types of reference materials in radio analytics solutions, matrix reference materials and some special reference objects are used. All classes of reference materials should be used depending on the purpose of the demonstration of quality, even in-house reference materials. Interlaboratory measurement comparison and performance evaluation programs play important quality assurance role in radio analytical laboratories. Fortunately, nowadays, the main task is to determine a very low radioactivity concentration in the environment; therefore, pre-concentration is necessary. Generally, the radionuclide bearing natural materials collected from sites where there had been sufficient time for natural processes to redistribute various chemically different species of radionuclides are more reliable reference materials than spiked materials—the main difference is the chemical bounding which is crucial from the point of view of the bioavailability. The need of reference material is summarized according to the intended use, like quality control, measurement validation, and instrument calibration. 相似文献
Ethyl (S)-3-hydroxy-3-phenylpropionate (S)-2 was obtained by the asymmetric reduction of ethyl 3-phenyl-3-oxopropionate 1 with the yeast Saccharomyces cerevisiae (ATCC 9080). The kinetic resolution of racemic ethyl 2-acetoxy-3-phenyl-propionate rac-3 with the same microorganism, gave after hydrolysis ethyl (R)- and (S)-3-hydroxy-3-phenylpropionates (R)-2 and (S)-2 which were converted by a straightforward series of reactions to the enantiomers of 3-amino-3-phenyl-propionic acids (S)-6 and (R)-6. The asymmetric reduction and hydrolytic kinetic resolution were also tested with several other whole cell systems under a variety of conditions. 相似文献
AbstractThe novel push–pull alkene, the 2-(nitro-nitrosomethylene)-pyrrolidine with numerous aliphatic or aromatic amines as nucleophiles afforded amidoximes. Various substituted oxadiazaborole and oxadiazole derivatives were prepared starting from these amidoximes, widening the synthetic applicability of the push–pull alkenes. Acylation of the amidoximes was also examined. The mechanism of the amidoxime formation was investigated by computational methods. 相似文献