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A fluorescent assay for Hg 2+ was developed based on magnetic separation and the formation of T-Hg 2+ -T base pairs. The aptamers were immobilized on the surfaces of magnetic beads to form aptamers-functionalized magnetic beads (AMB). In the absence of Hg 2+ , the signal transduction probe (STP) can combine with AMB through complementary base pairing. There is almost no STP in the detection solution after magnetic separation, which results in the fluorescence signal quite weak. The presence of Hg 2+ leads to the formation of T-Hg 2+ -T base pairs between aptamers and help DNA. After magnetic separation, Hg 2+ is separated from the system and STP is left in the solution, so the fluorescence signal was significantly enhanced. The fluorescence intensity linearly increased with the increasing of Hg 2+ concentration from 2 to 160 nM with the detection limit of 0.2 nM. This method has been successfully applied to test and quantify Hg 2+ in river water and ribbon fish with satisfactory recoveries, and the results were in full agreement with those from the atomic fluorescence spectroscopy (AFS). As-built method could avoid the direct binding of Hg 2+ with the fluorescent signal probe. Therefore, combining with magnetic separation, the heavy metal-fluorescence quenching effects could be effectively eliminated.

Sulfated zirconia-lanthana (SO42−/ZrO2-La2O3) precursors were prepared by ultrasonic coprecipitation method and followed by aging at different temperature. The precursors were treated by 0.5 mol/L H2SO4. Samples of SO42−/ZrO2-La2O3 nano-crystalline catalysts were obtained by baking the treated precursors at different temperatures. The acidic properties of SO42−/ZrO2-La2O3 were tested by the Hammett indicator method. The phase composition, specific area, particle structure, and surface state were characterized by X-ray diffraction, BET, transmission electron microscopy, infrared spectrum, and X-ray photoelectron spectroscopy. The catalytic activities were estimated by esterification of acetic acid with glycerin. It was shown that the catalyst prepared by ultrasonic stirring and low temperature (−15°C) exhibited highly active sites and high catalytic property.

Although it is impossible to manufacture identical columns for use in a simulated moving bed (SMB) process, theoretical studies assume that all the columns in an SMB unit have identical characteristics. In practice, calculations in modeling and optimization studies are made with the average values of each column parameter set. In this report, the effects on SMB process performance caused by column-to-column fluctuations of the parameters are discussed. As a first step, we show how the differences in porosity of the columns may be taken into account with a revised set of separation conditions. Reductions in the purity of the extract and the raffinate streams are quantitatively related to the column-to-column fluctuations of the retention times of the two components arising from these porosity differences. For the sake of simplicity, the discussion first addresses the case of a four-column SMB operating under linear conditions. Then, the scope is extended to the cases of SMB units incorporating several columns in each section and to SMB units operating under nonlinear conditions.

A new implementation of the equilibrium–dispersive model permits the study of problems requiring two-space dimensions for their modeling, such as a nonhomogeneous column with a cylindrical symmetry, a nonplanar injection with a cylindrical symmetry, or a cylindrical central injection. The migration and broadening of a cylindrical band coaxial with the column but narrower, moving along a homogeneous column is studied. The axial and radial profiles of the band inside the column and the elution profiles are calculated. These profiles depend on both the radial and the axial dispersion coefficients. The radial dispersion coefficient decreases with increasing mobile phase velocity and is usually low, much lower than the axial dispersion coefficient. Thus, the material in a relatively wide central injection made on a wide bore column may never have a chance to get close to the column wall. The clearance required at injection is estimated.

A Sorbex-type SMB separation instrument was operated for the separation of mixtures of 2-phenyl ethanol and 3-phenyl-1-propanol on a series of eight columns packed with Zorbax C18 bonded silica, using a 60:40 (v/v) solution of methanol and water as the mobile phase. The experiments were carried out with low-concentration mixtures under linear conditions. The elution profiles of both compounds between any two successive columns of the set under steady-state conditions were recorded while compositions of the raffinate and extract were measured. The four safety margin factors, β j , were divided into two groups: β 1 and β 4 ; β 2 and β 3 with different influence. Within the framework of the linear, ideal model of chromatography, a range of flow rates enables an SMB to operate successfully by completely separating the feed into its two components. The influence of different flow rates on the performance of the separator was studied by calculations and experiments with excellent agreement between both sets. With a simple optimization strategy, the four flow rates are selected to maximize the production rate or the concentration of extract and raffinate products, or to minimize the desorbent consumption. These optimum conditions are obtained by controlling the locations of concentration profiles inside the SMB. A reliable model for SMB operation allows a rapid and easy selection of the optimum experimental conditions.

A simulated moving bed (SMB) was operated for the separation of mixtures of 2-phenyl ethanol and 3-phenyl-1-propanol on columns packed with Zorbax C18 bonded silica, using a 60:40 (v/v) solution of methanol and water as the mobile phase. Series of four or eight columns were used. The experiments were carried out with low concentration mixtures, that is, under linear conditions. Band profiles of both compounds eluted from one of the columns during successive periods after steady state had been reached were recorded, as were the concentration histories at the extract and raffinate ports. These experimental results are compared to those predicted by two models: the linear ideal and the linear equilibrium-dispersive models of chromatography, applied to the SMB separator. These two models give excellent agreement between the experimental profiles and those calculated with the model. As expected, the profiles predicted by the ideal and the equilibrium-dispersive models differ only by the lack of dispersion in the profiles given by the former. The latter model is demonstrated to be a solid, reliable tool for further studies of the SMB design and optimization.

Columns were packed with alternating layers of virgin Zorbax C18 and blue colored Zorbax, treated with the dye Cibacron Blue. After consolidation of the column packing, the beds were extruded off the column, examined and photographed as they were, then cut along an axial plane, and these sections were examined and photographed. Evidence of radial heterogeneity of the distribution of the layers of the two packing materials in the bed after consolidation was observed. Friction of the bed along the column wall during consolidation was demonstrated.

Fundamental investigations of band profiles in nonlinear liquid chromatography have always assumed isothermal conditions. This is correct in linear, analytical chromatography, in which case the solute concentrations are very small and the influence of the heat of adsorption on the band profiles can always be neglected. However, this is no longer exact in nonlinear chromatography because the concentrations of the feed components are usually high. If the heat of adsorption is large enough, the chromatographic system cannot be considered as isothermal. The differential heat and mass balance equations are then coupled. Experimental data acquired in a typical case illustrate the effect. These data fit well to a lumped kinetic model with slow heat transfer kinetics. Further calculations suggest that the influence of the heat of adsorption on actual separations is small and could be negligible in almost all cases.

Simulated moving-bed (SMB) separators have been used successfully to separate or purify continuously two components with different adsorption selectivities. A detailed understanding of their behavior is still lacking, however. A numerical solution of the equilibrium—dispersive model allows the calculation of the concentration profiles along the columns, of their progressive shifts during a cycle, of the progressive build-up of these concentration profiles in each column during the start-up period, of the concentration profiles under steady-state and of the concentration histories at the extract and raffinate ports. These profiles are illustrated and discussed. The results obtained are compared to those of the exact analytical solution of the linear, ideal model previously developed. This comparison illustrates the influence of column efficiency on the time needed to reach steady-state operation.

The profiles of large-size system peaks and vacancies have been studied andcompared. A reversed-phase system was used with analytical-size column packed with ZORBAX C18 spherical particles and methanol-water as the mobile phase. The analyte was 3-phenyl-1-propanol. The equilibrium-dispersive model of chromatography was used to calculate band profiles using the measured isotherm data and the column efficiency. The isotherm data were determined using frontal analysis and could be fitted to a simple Langmuir equation. Excellent agreement was found between experimental and calculated results.

The elution band profiles of two partially separated components were calculated for a radially heterogeneous cylindrical column, using a modified equilibrium-dispersive model, assuming no radial dispersion. Steady-state flow-rate is assumed with a given cylindrical radial distribution of the velocity. The results show a marked degradation of the column performance when the ratio of the mobile-phase velocities at the column center and at the wall differs from unity by more than a few percent.

Performance and stability were tested for radial compression columns packed with spherical particles of an octadecyl bonded silica. The performance of the radial columns remained unchanged after approximately 500 h of constant use, including a number of solvent gradient runs. The performance of analytical columns packed with the same material was comparable to that of the radial columns. The column permeability decreases and the inlet pressure required to maintain a constant flow-rate increases with increasing radial compression pressure. Maximum column efficiency was obtained for a value of radial compression pressure approximately equal to 25 bar.

The onset of the nonlinear behavior of band profiles in elution chromatography is investigated by studying the profile of the shock layer caused by a finite mass transfer resistance in the absence of axial dispersion for a single component. A closed-form analytical expression of the shock layer is obtained for a parabolic isotherm. This solution depends on a dimensionless number which may be used to characterize the degree of nonlinear behavior of the band profiles and to select the model most appropriate for their accurate description. The profiles resulting from this solution are compared with those obtained by numerical calculations under different conditions to assess the influence of the assumptions made. The differences observed illustrate the sensitivity of the elution profiles to small changes in the equilibrium isotherm.

Elution band profiles are calculated for radially heterogeneous cylindrical columns, assuming an infinite rate of mass transfer kinetics and no axial dispersion. Steady-state flow-rate is assumed, with a given, cylindrical radial distribution of the velocity. Parabolic, cuspal and cosinusoidal distributions were studied, all three with either the velocity maximum or minimum in the column center. In all cases, strong changes in the band profiles appear for velocity distributions in which the ratio of the maximum to the minimum velocity is as low as 1.05. Some of the profiles obtained appear to be similar to experimental profiles.

In this paper, we report on the structural properties and superconductivity of Mg(B1-xCx)(2) compounds. Powder X-ray diffraction results indicate that the samples crystallize in a hexagonal AlB2-type structure. Due to the chemical activity of Mg powders, a small amount of MgO impurity phase is detected by X-ray diffraction. The lattice parameters decrease slightly with the increasing carbon content. Magnetization measurements indicate that the non-stoichiometry of MgB2 has no influence on the superconducting transition temperature and the transition temperature width. The addition of carbon results in a decrease of T-c and an increase of the superconducting transition width, implying the loss of superconductivity.

A variety of complementary evidence reviewed here demonstrates that the packing of chromatographic columns is heterogeneous. It is denser and less well organized close to the column wall than in the center of the column. The mechanism of particle consolidation under stress explains the origin of this phenomenon and provides a fundamental justification to what is known in column chromatography as "the wall effect".

The effects of the substitution of Li for Mg in Mg1-xLixB2(x=0, 0.1, 0.2) on their structure and superconductivity have been investigated. It has been found by X-ray diffraction that the substitution of Li for Mg with x=0.1 and 0.2 does not cause phase transformation in these samples. However, the measurements of temperature-dependent normalized magnetization indicate the loss of superconductivity with the increase of the Li content in these samples.

(Ag,Au)/Si nanocomposite films were deposited using the rf co-sputtering method. The absorption coefficient of Ag/Si nanocomposite film was calculated based on the Maxwell-Garnett theory and differential effective medium(DEM) theory;the experimental results of spectra agreed with the DEM theory.And the possible microstructure and the reason why the plasma resonance absorption peaks were broadened have been discussed.