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951.
952.
953.
The normal phase HPLC behavior of a bare zirconia column was studied at temperatures up to 200 °C using a hexane mobile phase. The use of elevated column temperatures significantly decreased the retention of twenty five aromatic model compounds according to the van't Hoff equation (>30-fold decrease for some compounds). Large improvements in peak shape, efficiency (>2.2-fold), aromatic group-type selectivity, and column re-equilibration times (>5-fold) were obtained at elevated temperatures. The thermal decomposition of two polar nitrogen compounds (indole and carbazole) was observed in a hexane/dichloromethane mobile phase at temperatures greater than 100 °C. The first order decomposition of carbazole was studied in further detail. 相似文献
954.
In theory, with identical stationary phase chemistry, the transfer of an HPLC method to UHPLC conditions is straightforward and necessitates the calculation of new conditions based on column and instrument geometries. Occasionally, undesirable changes in selectivity, retention or efficiency have been reported and have been attributed to a frictional heating phenomenon that is due to the elevated generated pressure drop. In the present study, the frictional heating in a UHPLC system was evaluated experimentally under gradient elution conditions (acetonitrile/buffer at pH 3 and 9) with generated pressure drops in the range of 100-1000 bar on both 1.0mm and 2.1mm I.D. columns using a mixture of 10 representative basic, acidic and neutral pharmaceutical compounds. Under adiabatic conditions (i.e., still-air oven), the longitudinal temperature gradient was estimated at +4 °C, +8 °C and +16 °C at 300, 600 and 1000 bar, respectively, on a 2.1mm I.D. column using an empirical measurement procedure. With the 1.0mm I.D. column, these values were reduced to +3 °C, +6 °C and +12 °C, respectively. Finally, various approaches to eliminate or at least to reduce the effect of frictional heating are briefly discussed. 相似文献
955.
基于支持向量机的高维特征非线性快速筛选与肽QSAR建模 总被引:1,自引:0,他引:1
以氨基酸的531个物理化学性质参数直接表征肽的结构, 基于支持向量回归发展了一种新的高维特征非线性快速筛选方法, 将其应用于苦味二肽和血管紧张素转化酶抑制剂2个肽体系的定量序效关系(QSAR)建模, 各筛选获得10个意义明确的保留描述子. 以保留描述子建立支持向量回归模型, 其拟合精度、留一法交叉测试精度和外部预测精度较文献报道结果均有较大幅度提升, 优势明显; 对所建模型进行了非线性回归显著性测验、单因子相对重要性显著性测验和单因子效应分析, 增强了模型的可解释性. 新方法在肽、蛋白质QSAR建模等高维数据回归预测领域有广泛应用前景. 相似文献
956.
Three novel conjugated polymers bearing 3,4-bis(4-hexylthiophen-2-yl)-3-cyclobutene-1,2-dione unit in their main chain have been synthesized successfully in good yields through Suzuki or Stille coupling reaction.Their molecular structures have been confirmed by FT-IR,1H NMR and 13C NMR.All these copolymers exhibit broad and strong absorption bands in UV-vis region,and their optical band gaps are calculated to be 1.6-2.0 eV.suggesting that they have good coverage with the solar spectrum.These polymers have good thermostability and solubility in common organic solvents.Moreover,all these objective macromolecules possess high electron affinity of~3.8 eV determined from cyclic voltammetry measurement,implying that they are potential n-type polymeric photovoltaic materials. 相似文献
957.
A novel high performance liquid chromatography-chemiluminescence(HPLC-CL) method for investigation of in vitro metabolism of repaglinide in pig liver microsomes with microdialysis sampling technique was developed.The chromatographic separation was performed on a Hypersil BDS-C18 column with an isocratic mobile phase consisting of methanol and 0.01 mol/L KH2PO4(pH 3.0)(volume ratio 75:25) at a flow rate of 1.0 mL/min.The detection was based on the chemiluminescence reaction of repaglinide with acidic potassium permanganate(KMnO4) and tris(2,2’-bipyridyl)ruthenium(Ⅲ)(Ru(bpy)33+),which was immobilized on the cationic ion-exchange resin for obtaining high sensitivity and reducing consumption of expensive reagent. 相似文献
958.
Er Fu Huoa Yong Zoua Hui Qin Sunb Yan Huang Zhi Yun Lua Qing Jianga a College of Chemistry.Sichuan University Chengdu China b Analytical & Testing Center Sichuan University China 《中国化学快报》2011,(11)
Three novel conjugated polymers bearing 3,4-bis(4-hexylthiophen-2-yl)-3-cyclobutene-1,2-dione unit in their main chain have been synthesized successfully in good yields through Suzuki or Stille coupling reaction.Their molecular structures have been confirmed by FT-IR,~1H NMR and ~(13)C NMR.All these copolymers exhibit broad and strong absorption bands in UV-vis region,and their optical band gaps are calculated to be 1.6-2.0 eV.suggesting that they have good coverage with the solar spectrum.These polymers... 相似文献
959.
960.
A GC-high-resolution isotope dilution MS (IDMS) method for the quantification of melamine in milk powder is described. The developed technique is compared to the LC-IDMS/MS technique, typically used for the determination of melamine in various matrices. The accuracy of the GC-high-resolution IDMS method was demonstrated when a small degree of equivalence was obtained in a regional comparative study involving the determination of melamine in milk powder. 相似文献