An on-line solid phase extraction (SPE) preconcentration system coupled to flame atomic absorption spectrometer (FAAS) was developed for determination of copper and cadmium at μg L−1 level. The method is based on the on-line retention of copper and cadmium on a microcolumn of alumina modified with sodium dodecyl sulfate (SDS) and 1,10-phenanthroline and subsequent elution with ethanol and determination by FAAS. The effect of chemical and flow variables that could affect the performance of the system was investigated. The relative standard deviation (n = 6) at 20 μg L−1 level for copper and cadmium were 1.4 and 2.2% and the corresponding limits of detection (based on 3σ) were 0.04 and 0.14 μg L−1, respectively. The method was successfully applied to determination of copper and cadmium in human hair and water samples. 相似文献
A spectrophotometric method was used for the molecular complexation of ICl3 with para-substituted meso-tetraarylporphyrins (H2t(4-X)pp; X: OCH3, CH(CH3)2, CH3, H and Cl) in methanol/chloroform (2.5% v/v) solution. The equilibrium constants and the thermodynamic parameters were measured
spectrophotometrically at various temperatures for 1:1 molecular complex formation of meso-tetraarylporphyrins as electron
donors with ICl3 as the electron acceptor. The formation constants for the molecular complexes change according to the following trend: [ICl3(H2t(4-OCH3)pp)]>[ICl3(H2t(4-CH(CH3)2)pp)]>[ICl3(H2t(4-CH3)pp)]>[ICl3(H2tpp)]>([ICl3(H2t(4-Cl)pp)]. Further, the thermodynamic parameters, ΔGo,ΔHo and ΔSo, for formation of the complexes were obtained. 相似文献
The purpose of this paper is to introduce and to discuss the concept of approximation preserving operators on Banach lattices with a strong unit. We show that every lattice isomorphism is an approximation preserving operator. Also we give a necessary and sufficient condition for uniqueness of the best approximation by closed normal subsets of X+, and show that this condition is characterized by some special operators. 相似文献
Novel binary mixtures have been prepared between an optically active antiferroelectric liquid crystal, (S)-4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxy-biphenyl-4-carboxylate, and an optically active twin liquid crystal, (R)-3-methyladipic acid bis[4-(5-octyl-2-(pyrimidinyl)phenyl] ester, and the liquid crystalline properties investigated. The stability of each liquid crystal phase was found to decrease by mixing these two liquid crystalline materials. Furthermore, a phase diagram between these compounds showed a clear discontinuity in phase sequences. These results indicate that the liquid crystal phases are different in nature between these materials. The mixture consisting of the antiferroelectric material (40 per cent) and the twin material (60 per cent) shows an unusual liquid crystal phase, where the texture is similar to that reported for the twist grain boundary (TGB) phase. Related binary mixtures have been prepared between optically active or racemic materials, where the chirality of the system is expected to be altered systematically. The TGB phase was found to be induced only in the mixture between the optically active materials. Two kinds of effect on the appearance of the TGB phase, i.e. a strong helical structure induced by the optically active twin liquid crystal and a decrease of the smectic layer strength achieved by mixing between two types of liquid crystalline materials, are discussed. 相似文献
Triplet excited unsymmetrically substituted benzils react with 2-morpholinopropenenitrile to form oxetanes. Whereas the selectivity with respect to the site of addition (benzoyl vs. 4-substituted benzoyl) is generally low, the photoadditions observed are all unidirectional (regioselective) and of high stereoselectivity, as had also been found earlier for benzil itself and for symmetrically 4,4-disubstituted benzils. The relative configurations of two oxetanes have been unambiguously confirmed by single crystal X-ray structure determinations. 相似文献
The use of imaging techniques has become an essential tool in cell biology. In particular, advances in fluorescence microscopy and conventional transmission electron microscopy have had a major impact on our understanding of chromatin structure and function. In this review we attempt to chart the conceptual evolution of models describing the organization and function of chromatin in higher eukaryotic cells, in parallel with the advances in light and electron microscopy over the past 50 years. In the last decade alone, the application of energy filtered transmission electron microscopy (EFTEM), also referred to as electron spectroscopic imaging (ESI), has provided many new insights into the organization of chromatin in the interphase nucleus. Based on ESI imaging of chromatin in situ, we propose a 'lattice' model for the organization of chromatin in interphase cells. In this model, the chromatin fibers of 10 and 30nm diameter observed by ESI, produce a meshwork that accommodates an extensive and distributed interchromosomal (IC) space devoid of chromatin. The functional implications of this model for nuclear activity are discussed. 相似文献
We compare the benefits of spatial and spectral priors in near-infrared diffuse tomography image reconstruction. Although previous studies that incorporated anatomical spatial priors have shown improvement in algorithm convergence and resolution, our results indicate that functional parameter quantification by this approach can be suboptimal. The incorporation of a priori spectral information significantly improves the accuracy observed in recovered images. Specifically, phantom results show that the maximum total hemoglobin concentration ([Hb(T)]) in a region of heterogeneity reached 91% of the true value compared to 63% using spatial priors. The combination of both priors produced results accurate to 98% of the true [Hb(T)]. When both spatial and spectral priors were applied in a healthy volunteer, glandular tissue showed a higher [Hb(T)], water fraction, and scattering power compared to adipose tissue. 相似文献
The electrochemical hydrogen storage properties of Ni-supported multi-walled carbon nanotube (Ni/MWCNT) electrodes were investigated using charge/discharge (C&D) and cyclic voltammetry (CV) techniques. Nickel NPs were deposited on the MWCNT surface, which was first chemically oxidized by H2SO4 and HNO3 (3:1, v/v). Hydrogen storage was carried out by using the Ni/MWCNT electrode as the working electrode in the electrochemical cell. A set of various current densities were applied to the cell to produce (C&D) cycles, and it became optimum corresponding to 1.5 mA current. According to the electrochemical test results, the highest electrochemical discharge capacity of 1625 mAh g?1 was obtained for the electrode with ratio of 4:1 (MWCNTs to Ni) in the initial cycle, which corresponded to 6.07 wt% H2. The storage capacity was increased and reached to 4909 mAh g?1 (18.34 wt% H2) after 20 cycles, and the electrode maintained the specific capacity as cycling continued. Thus, the Ni/MWCNT electrode displays an excellent cycle stability and a high capacity reversibility. CV measurements also showed that the electrochemical adsorption and desorption amount of hydrogen was increased by Ni loading onto the CNTs and indicated that the electrochemical hydrogen adsorption of the electrode has an activated period. 相似文献
In this paper, we present a new colorimetric technique as a novel assay for the easy and direct detection of α-amylase activity. This detection system utilizes the interaction of α-amylase with starch that is supporting copper/gold (Cu/Au) nanoclusters. The Cu/Au nanoclusters are synthesized using starch as a stabilizing agent at room temperature. These nanoclusters show robust peroxidase-like activity and are able to catalyze the oxidation of TMB (3,3,5,5-tetramethylbenzidine) in the presence of hydrogen peroxide (H2O2), leading to the generation of a blue-colored solution. The α-amylase detection mechanism is based on the digestion of the starch by α-amylase, which results in nanocluster aggregation, leading to increased nanoparticle size and thus decreased peroxidase-like activity of the Cu/Au NCs. Experiments showed that the gradual addition of α-amylase causes the peroxidase activity to decrease step by step in a linear fashion. Using this method, colorimetric sensing of α-amylase was achieved with a detection limit (LOD) of 0.04 U/mL and a linear range of 0.1–10 U/mL. This method is significantly selective for α-amylase and could be affordably and conveniently applied to the detection of α-amylase in blood serum.