Determination of dichlorvos by on-line microwave-assisted extraction coupled to headspace solid-phase microextraction and gas chromatography-electron-capture detection

The pretreatment technique of microwave-assisted extraction on-line headspace solid-phase microextraction (MAE-HS-SPME) was designed and studied for one-step in-situ sample preparation prior to the chromatographic analysis of a pesticide on vegetables. The pesticide on chopped vegetables was extracted into an aqueous solution with the aid of microwave irradiation and then directly onto the SPME fiber in headspace. After being collected on to the SPME fiber and desorbed in the GC injection port, the pesticide (dichlorvos) was analyzed with a GC-electron-capture detection system. The optimum conditions for obtaining extraction efficiency, such as the pH, the polarity modifier, and the salt added in sample solution, the microwave irradiation, as well as the desorption parameters were investigated. Experimental results indicated that the proposed MAE-HS-SPME technique attained the best extraction efficiency of 106% recovery under the optimized conditions, i.e. irradiation of extraction solution (10% aqueous ethylene glycol) at pH 5.0 with medium microwave power for 10 min. Desorption at 220 degrees C for 3 min offered the best detection result. The detection was linear at 5-75 microg/l with correlation coefficient of 0.9985. Detection limit was obtained at approximately 1.0 microg/l level based on S/N=3. The proposed method provided a very simple, fast, and solvent-less procedure to collect pesticides directly from vegetables for GC determination. Its application was illustrated by the analysis of trace dichlorvos in vegetables.     

Reversible replication between ordered mesoporous silica and mesoporous carbon

Highly ordered mesoporous silica can be regenerated from a mesoporous carbon CMK-3 that is a negative replica of mesoporous silica SBA-15, indicating reversible replication between carbon and inorganic materials.     

Effect of Hyperbranched Polyester on Modification of Epoxy Resins Cured with Anhydride

Epoxy resins are widely used in coatings, adhesives and polymer composites, but the applications of cured epoxy resins are often restricted by their poor toughness. HBP can be used as toughener to improve the toughness of epoxy resins due to its high-dens…     

Ethanol production from steam-explosion pretreated wheat straw

Bioconversion of cereal straw to bioethanol is becoming an attractive alternative to conventional fuel ethanol production from grains. In this work, the best operational conditions for steam-explosion pretreatment of wheat straw for ethanol production by a simultaneous saccharification and fermentation process were studied, using diluted acid [H₂SO₄ 0.9% (w/w)] and water as preimpregnation agents. Acid-or water-impregnated biomass was steam-exploded at different temperatures (160–200°C) and residence times (5, 10, and 20 min). Composition of solid and filtrate obtained after pretreatment, enzymatic digestibility and ethanol production of pretreated wheat straw at different experimental conditions was analyzed. The best pretreatment conditions to obtain high conversion yield to ethanol (approx 80% of theoretical) of cellulose-rich residue after steam-explosion were 190°C and 10 min or 200°C and 5 min, in acid-impregnated straw. However, 180°C for 10 min in acid-impregnated biomass provided the highest ethanol yield referred to raw material (140 L/t wheat straw), and sugars recovery yield in the filtrate (300 g/kg wheat straw).     

One step isolation and purification of liquiritigenin and isoliquiritigenin from Glycyrrhiza uralensis Risch. using high-speed counter-current chromatography

High-speed counter-current chromatography (HSCCC) technique in semi-preparative scale has been successfully applied to the separation of bioactive flavonoid compounds, liquiritigenin and isoliquiritigenin in one step from the crude extract of Glycyrrhiza uralensis Risch. The HSCCC was performed using a two-phase solvent system composed of n-hexane-ethyl acetate-methanol-acetonitrile-water (2:2:1:0.6:2, v/v). Yields of liquiritigenin (98.9% purity) and isoliquiritigenin (98.3% purity) obtained were 0.52% and 0.32%. Chemical structures of the purified liquiritigenin and isoliquiritigenin were identified by electrospray ionization-MS (ESI-MS) and NMR analysis.     

A theoretical study of bond selective photochemistry in CH2BrI

Bromoiodomethane photodissociation in the low-lying excited states has been characterized using unrestricted Hartree-Fock, configuration-interaction-singles, and complete active space self-consistent field calculations with the SDB-aug-cc-pVTZ, aug-cc-pVTZ, and 3-21g** basis sets. According to the results of the vertical excited energies and oscillator strengths of these low-lying excited states, bond selectivity is predicted. Subsequently, the minimum energy paths of the first excited singlet state and the third excited state for the dissociation reactions were calculated using the complete active space self-consistent field method with 3-21g** basis set. Good agreement is found between the calculations and experimental data. The relationships of excitations, the electronic structures at Franck-Condon points, and bond selectivity are discussed.     

三甲氧基苄啶分子印迹整体柱的制备及色谱性能

选择甲基丙烯酸为功能单体\, 甲基丙烯酸乙二醇双酯为交联剂, 制备了三甲氧基苄啶分子印迹整体柱, 对整体柱材料的形貌进行了表征, 并且研究了TMP和5种磺胺类药物在分子印迹整体柱上的色谱行为.     

CF3C(O)F水合作用的热力学和动力学理论研究

由于氟氟烃（CFCs）对大气臭氧层有破坏作用，人们拟以另外的化合物来代替它，CF3CX2H（X＝H，CI，F）可能是一类合适的取代物．但人们对它及其反应产物对大气的影响还不清楚.CFaC（0）F是CFaCX。H大气光氧化过程的终产物之一[1－3］，其在大气中的后继反应行为将直接关系到CF2     

含杂环羧酸基二苄基锡(Ⅳ)配合物的合成与表征

以二苄基二氯化锡和杂环羧酸钠为原料合成了十种新的有机锡配合物(PhCH₂)₂Sn(O₂CR)_nCl_2-n(n=1或2，R=杂环)。用元素分析、IR、 ¹H NMR和TG表征了配合物的组成和结构。     

Studies on Thermodynamics Features of the Interaction between Imidacloprid and Bovine Serum Albumin

At different temperatures, the interactions between imidacloprid （IMI） and bovine serum albumin （BSA） were investigated with a fluorescence quenching spectrum, a synchronous fluorescence spectrum, a three-dimensional fluorescence spectrum and an ultraviolet-visible spectrum. The average values of bonding constants （KLB： 3.424 × 10^4 L,mol^-1）, thermodynamic parameters （△H： 5.188 kJ,mol^-1, △G^（○—）：-26.36 kJ,mol^-1, △S： 103.9 J,K^-1,mol^-1） and the numbers of bonding sites （n： 1.156） could be obtained through Stern-Volmer, Lineweaver-Burk and ther- modynamic equations. It was shown that the fluorescence of BSA could be quenched for its reactions with IMI to form a certain kind of new compound. The quenching belonged to a static fluorescence quenching, with a non-radiation energy transfer happening within a single molecule. The thermodynamic parameters agree with △H〉 0, △S〉0 and△G^（○-）〈0, suggesting that the binding power between IMI and BSA should be mainly a hydrophobic interaction.