Selective Solid Phase Extraction and Pre-Concentration of Heavy Metals from Seawater by Physically and Chemically Immobilized 4-Amino-3-Hydroxy-2-(2-Chlorobenzene)-Azo-1-Naphthalene Sulfonic Acid Silica Gel

4-Amino-3-hydroxy-2-(2-chlorobenzene)-azo-1-naphthalene sulfonic acid (AHCANSA) was used as a chelating modifier to improve the reactivity of the silica gel surface in terms of selective binding and extraction of heavy metal ions. The surface coverage values were found to be 0.488 and 0.473mmolg^–1 for the newly modified physically adsorbed silica gel phase (I) and chemically immobilized-AHCANSA phase (II), respectively. The modified silica gel phases (I, II) were tested for stability in different acidic buffer solutions (pH 1–6) and found to be highly resistant to hydrolysis and leaching by buffer solutions above pH 2. The application of these two phases as solid extractors for a series of mono-, di-, and tri-valent metal ions from aqueous solutions was also performed with different controlling factors such as the pH value of metal ion solutions and equilibrium shaking time. The mmolg^–1 metal capacity values determined by silica gel phases (I, II) were found to confirm high affinity and selectivity characters for binding with heavy metal ions such as Cr³⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ in a range of 0.250–0.483. The tested alkali and alkaline earth metals, Na⁺, K⁺, Mg²⁺ and Ca²⁺, were found to exhibit little interaction and binding ability with the modified silica gel phases. The selectivity characters incorporated into the modified silica gel phases were further utilized and applied in solid phase extraction and pre-concentration of trace concentration levels (1.0µgmL^–1 and 2.00–2.50ngmL^–1) from real seawater samples. The percentage recovery values determined for Cr³⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were found to be in the range of 95.2–98.1±2.0–5.0%, and the pre-concentration recovery values for the same tested heavy metal ions were found to be in the range of 92.5–97.1±3.0–6.0% for the two newly modified silica gel phases with a pre-concentration factor of 500.Received December 20, 2002; accepted May 14, 2003 published online September 1, 2003     

混合模式硅胶基质毛细管电色谱整体柱的制备及其电色谱性能研究

采用温和条件下的溶胶-凝胶技术，成功制备了阴离子交换-反相混合模式硅胶基质毛细管电色谱整体柱。通过调整反应液中不同前体的比例，优化了整体柱的制备条件。通过扫瞄电镜，对柱床进行了表征和分析。实验发现，所制备的整体柱电渗流的方向和大小可随流动相pH值的改变而改变，在酸性和中性条件下，具有从阴极流向阳极的电渗流；当流动相pH值升至约7．5时，电渗流方向发生了反转（由阳极流向阴极）。在优化的实验条件下，用所制备的整体柱对所考察的酸性（中性）化合物实现了快速分离，并获得了高达160，000N／m的柱效。     

Thermodynamic evaluation of a partial charge model assumptionfor the dissolved silica system

The Partial Charge Model was developed to predict the hydroxylation, polymerization, and precipitation of ions. The purpose of this study is to evaluate the Partial Charge Model for describing the polymerization of silica in aqueous solutions. The Partial Charge Model predicts the stability of ions and complexes based on the assumption that the stable species will have the same electronegativity as the mean electronegativity of the solution. The silica system was chosen for model validation because of the rare availability of self-consistent thermodynamic data on many dissolved but polymerized silicate anions, including both linear and cyclical species. The electronegativity of each species was calculated using the Partial Charge Model and the results were plotted against the stability constants for the ions. The silicate anions segregated into groups on the plot based on the number of charges per silicon atom in the polymer. Plots of the log of the stability constant versus the change in electronegativity produced a linear relationship for the silica polymers containing one negative charge per silicon atom, which resulted in an r ² of 0.9978. Thus, the Partial Charge Model successfully describes the thermodynamics of silica polymerization in aqueous solution for species that are sufficiently alike, but was not accurate for all silica species.     

Effect of the modification of silica on thermal properties and flammability of cross-linked butadiene-acrylonitrile rubbers

The paper presents the results of testing the thermal stability and flammability of butadiene-acrylonitrile rubber vulcanizates with different contents of combined acrylonitrile: Perbunan NT 1845 and Perbunan NT 3945 from Bayer, containing unmodified and bromine- or iodine-modified silica. The test results were obtained with the use of a derivatograph, measurements of flammability by the method of oxygen index, in air and also with the use of a cone calorimeter. The effect of the modification on the zeta potential was also examined. A considerable reduction in the flammability of nitrile rubber vulcanizates filled with silica can be obtained by the modification of filler with bromine or iodine. All the vulcanizates containing modified silica are self-extinguishing. An appropriate filling of NBR 39 vulcanizates with bromine-modified silica makes it possible to obtain non-flammable polymeric materials. They neither ignite nor glow under the action of a flame source for 30 s. The findings can be a rational basis for the synthesis of modified silica that can act as active filler and effective flame-retardant agent at the same time.     

Preparation and characterization of silicate gel glasses containing Cr2O3

The effect of thermal treatment on the structural incorporation of Cr₂O₃ in xCr₂O₃·(100 – x)SiO₂ and 5R _n O·xCr₂O₃·(95 – x)SiO₂ (where x=0.01–1 mol.% and R=Li, Na and Ca) gel glasses was studied by optical absorption spectrophotometry, DTA-TG, XRD and electron microscopy.Samples heat treated at 60°C have green color due to the presence of Cr³⁺ in octahedral coordination. The optical transmission, and color (yellow, orange or ambar), of the samples heat treated between 200 and 700°C prove that Cr³⁺ (octahedrally coordinated) and Cr⁶⁺ (tetrahedrally coordinated) are both present. Segregation of Cr₂O₃ take place at temperatures above 800°C.In reducing conditions the gel glasses were green due to the presence of a high content of Cr³⁺ ions. Samples containing Li or Na show crystalline phases at temperatures below 850°C.     

Deactivation of fused silica capillary columns with cyanopropylhydrosiloxanes

A method is described for surface deactivation and modification of fused silica capillary columns with a cyanopropyl-containing reagent. The deactivation procedure involved a dehydrocondensation reaction between a bis(cyanopropyl)methylhydropolysiloxane reagent and surface silanol groups at an optimum temperature of only 250°C. Actual critical surface tension measurements were made using the capillary rise method. Excellent deactivation for acidic and basic compounds at the low ng level, and wettability for nonpolar and polar polysiloxane stationary phases were obtained. A procedure was developed to remove acidic impurities that are present in polar stationary phases.     

Thermal analysis of PMMA/gel silica glass composites

Thermal analysis of poly-methylmethacrylate (PMMA) impregnated porous gel silica glasses confirms that the PMMA chains form hydrogen bonds with the pore surface silanol groups. The adopted conditions for the insitu polymerisation result in about 4% of residual monomers trapped in the polymer, most of them in the amorphous structure. The polymer and monomer mixture takes up the whole of the free pore volume. Most of the residual monomer polymerises during the DSC scans above the glass transition temperature providing an excellent probe for the weak glass transition. Polymerisation in the gel silica glass medium affects the glass transition temperature, the length of polymer chains, and the degree of polymerisation.     

负载型双噁唑啉催化剂上的不对称Diels-Alder反应

 分别以乙烷桥键磺酸官能化的有机-无机杂化介孔材料、十二钨磷酸铯、活化硅胶以及SBA-15为载体,通过非共价键作用制备了负载型双噁唑啉催化剂,并将该催化剂用于催化3-((E)-2-丁烯酰基)-1,3-噁唑啉-2-酮和环戊二烯的不对称Diels-Alder反应. 研究表明,催化剂的性能取决于载体本身以及载体表面阴离子的性质. 以SBA-15为载体时产物的对映体选择性较低,可归因于载体表面较低的羟基浓度.     

Effect of the Measurement Temperature on the Dispersive Component of the Surface Free Energy of a Heat Treated SiO2 Xerogel

The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, _S ^D, vary from 49.07 mJ·m^–2 at 25°C to 17.20 mJ·m^–2 at 150°C. The _S ^D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of _S ^D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the _S ^D values as well as in the dispersive component of the surface enthalpy, h _S ^D. Such abrupt change can be attributed to an entropic contribution of the surface free energy.     

亲水作用色谱法测定表阿霉素及其杂质

建立了一种以亲水作用色谱分离测定表阿霉素的新方法。采用硅胶色谱柱及高极性有机溶剂水相缓冲溶液流动相。对流动相的pH、缓冲溶液的浓度及流速进行了优化,确定了以乙腈甲酸钠缓冲溶液(pH2.9)(90∶10,V/V)作为流动相的最佳条件。对优化的分离条件进行系统适应性实验,结果表明表阿霉素与有关杂质之间的分离度和拖尾因子均达到药典要求。该法具有良好的线性(相关系数0.9971～0.9991)和重复性(峰面积RSD<1.0%),方法简便实用,用于实际样品分析,结果满意。