Innovative chemically bonded ionic liquids-based sol-gel coatings as highly porous, stable and selective stationary phases for solid phase microextraction

In this work, two allyl-functionalised ionic liquids (ILs), 1-allyl-3-methylimidazolium hexafluorophosphate and 1-allyl-3-methylimidazolium bis(trifluoromethanesulphonyl)imide, were used as selective coating materials to prepare chemically bonded ILs-based organic-inorganic hybrid solid phase microextraction fibres. These fibres were prepared with the aid of γ-methacryloxypropyltrimethoxysilane as bridge using sol-gel method and free radical cross-linking technology. The underlying mechanisms of the sol-gel reaction were proposed, and the successful binding of these functional ILs to the sol-gel substrate was confirmed by Fourier transform infrared spectroscopy. These IL-based sol-gel coatings had porous surface structure, high thermal stability, a wide range of pH stability, strong solvent resistance and good coating preparation reproducibility. They also had high selectivity and sensitivity towards strong polar phenolic environmental estrogens (PEEs) and aromatic amines due to the strong electrostatic interactions, hydrogen bonding and π-π interactions provided by the special molecular structure of these imidazolium ILs. Moreover, their characteristics were somewhat different depending on the type of anions in the IL structure. The practical applicability of these IL-based sol-gel coatings was evaluated through the analysis of PEEs in two real water samples. The detection limits were quite low, varying from 0.0030 to 0.1248 μg L⁻¹. The linearity was very good in the range of 0.1 to 1000 μg L⁻¹ for most analytes, and the relative standard deviation values were below 6%. The relative recoveries were between 83.1 and 104.1% for lake water and between 89.1 and 97.1% for sewage drainage outlet water.     

烟酸分子印迹复合膜的制备及其分离性能研究

以聚偏氟乙烯微孔滤膜为支撑膜,烟酸为模板分子,用紫外光引发表面修饰聚合制备了微孔滤膜支撑-烟酸分子印迹复合膜.电镜扫描对该印迹复合膜进行了表面形态表征.Scatchard分析表明,在所研究的浓度范围内分子印迹复合膜中存在等价的结合位点,结合位点的平衡离解常数Kd为5.55×10-2mmol·L-1.底物的结合和渗透选择性实验表明,分子印迹复合膜对烟酸有较好的结合性能,结合量是6.10μmol·g-1.与其结构类似的化合物烟酰胺相比,分子印迹复合膜对模板分子展示了更好的选择性及高度的识别能力.     

Mass transfer mechanism in liquid chromatography columns packed with shell particles: Would there be an optimum shell structure?

The mass transfer mechanisms in columns packed with old (55 μm Zipax and 5 μm Poroshell) and recently commercialized shell particles (2.7 μm Halo-C(18) and Kinetex-C(18)) were investigated from a physico-chemical point of view. Combining a model of diffusion in heterogeneous packed beds (effective medium theory) with values of the heights equivalent to a theoretical plate (HETPs derived from the first and second central moments of the elution profiles) and of the peak variances provided by the peak parking method, we demonstrate that columns packed with current shell particles perform better than those packed with fully porous particles in resolving low molecular weight compounds because the eddy diffusion term of the van Deemter equation of the former is markedly smaller. The calculation of eddy diffusion in column beds suggests that the smaller A terms are due to smaller trans-column velocity bias in columns packed with shell particles. We also show that the mass transfer of large molecules (e.g., proteins) is faster when the internal volume accessible to the analyte increases. Therefore, it is suggested that shell particles made of concentric layers with average pore sizes increasing with increasing diameter would provide columns with higher efficiency.     

Gas chromatographic retention in uncoated fused silica capillaries

Understanding of retention in uncoated fused‐silica capillaries is of interest due to increased attention on precolumn backflushing in capillary GC. Uncoated capillaries offer several advantages as precolumns compared to coated precolumns. In order to examine the possibility of predicting elution temperatures of alkanes from uncoated capillaries a priori, several sizes of deactivated but uncoated fused‐silica capillaries were evaluated under various operating conditions. Retention was found to depend on dimensionless ramp rate (°C/t_M), sample loading (capacity), flow mode, and column dimensions (probably related to surface area).     

科技创新投入影响经济增长的内在机制——基于中国实际经济运行的经验证据(1978-2005)

科技创新是促进经济增长的源泉和转变经济增长方式的关键,那么科技创新投入对经济增长是否存在积极影响?本文运用时间序列方法,在4变量系统内检验了我国科技创新投入与经济增长的内在关系,实证结果显示:①经济增长和固定资本投资、劳动投入、科技创新投入之间存在着长期均衡的协整关系;②科技创新投入对经济增长具有Granger影响,科技创新投入增加会导致经济增长;③在1-15年滞后期内,科技创新投入对经济增长的短期冲击为正向效应。在实证基础上,进一步分析了科技创新投入对经济增长的作用机理和路径依赖,并由此得出相关结论与政策建议。     

中国汽车产业内外资企业生产效率研究

文章利用教据包络分析法(DEA)结合Malquist指数分解对中国汽车产业内资企业和外资企业1998年～2005年的生产效率的变化进行了实证分析.研究结果表明,内外资企业的技术效率存在明显差距;Malquist生产率指数构成表明,中国汽车产业的全要素生产率总体呈现正增长的趋势,主要源自技术进步的拉动;内资企业近年来技术进步明显,成为拉动生产率增长的主要动力,外资企业对我国汽车产业全要素生产率的改善以及推动产业技术进步起到了积极的推动作用.     

轨道交通产业全产业链的韧性-脆弱性研究

首先,论述了韧性-脆弱性理论,界定了韧性-脆弱性的内涵．其次,分析了全产业链的产业韧性-脆弱性的形成机理,包括全产业链韧性-脆弱性和轨道交通产业全产业链韧性-脆弱性两个概念的界定．第三,构建了轨道交通产业全产业链韧性-脆弱性评价指标,内部评价指标来自于企业管理水平等5个影响因子,外部评价指标来自于资源禀赋等3个影响因子．第四,实证分析了轨道交通产业全产业链韧性-脆弱性评价,得出8个指标分别影响该产业全产业链韧性-脆弱性的情况是：企业规模、技术密集度、交通成本和对外开发程度这4个指标的影响显著,劳动力成本对产业影响程度不大,消费购买力和专利申请数及政策支持影响不显著．最后,从提高产业技术创新能力等5个方面,提出缓解轨道交通产业全产业链韧性-脆弱性的对策建议．     

A sol-gel-based amino functionalized fiber for immersed solid-phase microextraction of organophosphorus pesticides from environmental samples

A method based on immersed solid-phase microextraction (SPME) and gas chromatography mass spectrometry detection (GC-MS) for the determination of organophosphorous pesticides (OPPs) in aqueous samples was developed. A sol-gel based coating fiber was prepared using 3-(trimethoxysilylpropyl) amine as precursor. The synthesized fiber was prepared in a way to impart polar moiety into the coating network and would be more suitable for extracting polar and semi-polar organic pollutants. Important parameters influencing the extraction process were optimized and an extraction time of 40 min at 30 °C gave maximum peak area, when NaCl (20% w/v) was added to the aqueous sample. The linearity for disulfoton, phorate and sulfotep was in the concentration range of 0.01 to 5 ng mL^− 1 and for parathion and O,O,O-triethylthiphosphate was in the range of 0.01 to 50 ng mL^− 1. Limits of detection ranged from 1 ng L^− 1, for parathion, to 0.05 ng L^− 1, for disulfoton using time-scheduled selected ion monitoring (SIM) mode, and the RSD% values were all below 10.5% at the 1 ng mL^− 1 level. The developed method was successfully applied to real water samples while the relative recovery percentages obtained for the spiked water samples were from 80 to 115%.     

氮化铝粉体制备工艺研究

以氢氧化铝为铝源,乙炔黑为碳源,采用碳热还原和铝粉直接氮化同时进行,并辅以微波加热的新工艺制备了氮化铝粉体。结果表明,采用该工艺在反应温度为1300℃、反应时间为1h的条件下能获得氮化率高且分散性能良好的氮化铝粉末,该工艺反应活化能仅为常规碳热还原法所需活化能的1/4。     

Digital game‐based learning for K–12 mathematics education: A meta‐analysis

Digital games (e.g., video games or computer games) have been reported as an effective educational method that can improve students' motivation and performance in mathematics education. This meta‐analysis study (a) investigates the current trend of digital game‐based learning (DGBL) by reviewing the research studies on the use of DGBL for mathematics learning, (b) examines the overall effect size of DGBL on K‐12 students' achievement in mathematics learning, and (c) discusses future directions for DGBL research in the context of mathematics learning. In total, 296 studies were collected for the review, but of those studies, only 33 research studies were identified as empirical studies and systematically analyzed to investigate the current research trends. In addition, due to insufficient statistical data, only 17 out of the 33 studies were analyzed to calculate the overall effect size of digital games on mathematics education. This study will contribute to the research community by analyzing recent trends in significant DGBL research, especially for those who are interested in using DGBL for mathematics education.