Selectivity tuning of serially coupled columns in high performance liquid chromatography

The tuning of selectivity by changing the flow rate has been investigated in HPLC: two columns with different retention characteristics were coupled in series via a T-piece and the relative retention of components chromatographed on the system were changed by varying the individual flow rates in the coupled columns. The flow rate alteration was performed by adding a second flow after the first column. The flow rate ratio necessary for optimum resolution can be easily calculated on the basis of the capacity factors measured on the individual columns. The performance of this method for adjusting selectivity has been demonstrated by using different column combinations to separate several mixtures containing chlorophenols, nitroaromatic compounds, and aromatic hydrocarbons.     

A comparative study of hydrophobicity of octadecyl and alkylamide bonded phases based on methylene selectivity

The conformational dynamics of home‐made monomeric and polymeric (octadecyl – C18 and alkylamide – AP) stationary phases have been investigated by analyzing the dependence of retention on the reciprocal temperature for different organic compounds. Theoretical considerations were based on the results of methylene selectivity determination. Two selected PAHs – naphthacene and benzo[a]anthracene, whose structures differ in the position of the ring – were chosen as solutes to study the thermodynamics of retention behavior. Standard enthalpies (ΔH ⁰) were obtained from the slope of the plots of the capacity factor logarithm (ln k) against the reciprocal temperature (1/T), i. e. van't Hoff plots, in a temperature range from 285 to 315 K. The conformation of the stationary phase (monomeric and polymeric) structure and the length of bonded ligands with their specific functional (N‐acylamide) groups had a significant effect on retention.     

计算机法选择混合固定相最佳配比的研究

本文设计了1个BASIC计算程序，可以对任一混合物进行N种固定液最佳混合配比的计算，同时给出了26种物在4种常用固定液上的实验数据，并进行了2个实际样品的分离实验，证明通过计算机所选择的混合固定相的最佳配比是令人满意的。     

乙炔在钍配合物催化体系下的聚合

<正> 聚乙炔掺入杂质后,做为高分子导电材料已引起人们的极大关注。有关聚乙炔(下称PA)的合成、结构及性能测试,以及电池研究已有很多报道,其催化剂体系已有关于Ti、V、Cr、W、Fe、Mo、Ni和Co等过渡金属化合物,稀土化合物合成PA的报道。本文进行了应用重元素钍的高配合物[Th(P_(204))_8Cl_4]与三乙基铝组合作为催化剂、使乙炔在常温下定向聚合的研究,得到具有余属光泽银白色的PA,顺式含量为80％,并对PA薄     

气相色谱固定液极性和选择性评价

对非同族化合物溶质在两种固定相上保留值的关系进行了理论推导，并将该方程应用于８９种常见固定相的极性和选择性的评价。固定相的极性可用Ｂ值来评价，而选择性则用Ｂ、Ｔ３＾ａ，Ｃ３β值来评价。用该方程评价固定相具有两个优点，一是基于分子间作用力来评价固定相；二是探针化合物的选择不再受限制。     

Gaussian basis sets for CO2 molecule generated with the molecular improved generator coordinate Hartree–Fock method

The molecular improved generator coordinate Hartree–Fock (MIGCHF) method is used to generate increasing size atom-centered Gaussian basis sets for the CO₂ molecule. From these basis sets total HF energies and second-order correlation energies were calculated and compared with results obtained with other approaches. Considering our largest basis set, the HF energy is in error by 98 hartree and the second-order correlation energy corresponds to 95.6% of an estimate of the limiting value. The relevance of the present calculations is to show the accuracy that can be achieved in studies of small polyatomic molecules with the MIGCHF method.Acknowledgement We acknowledge the financial support of CNPq (Brazilian Agency). We employed computational facilities at Universidade Federal do Espírito Santo and Universidade Estadual Paulista (IQ Araraquara).     

基于扰动观测器的内置式PMSM无传感器控制

针对两相静止坐标系下基于观测器进行IPMSM无传感器控制时存在电角度估算误差与交直轴电感和负载转矩耦合、电角度补偿复杂等问题,文中选择在同步旋转坐标系下采用电机原有电感参数进行IPMSM无传感器控制。通过建立PMSM 的矢量数学模型,对存在电角度估算误差时采用IPMSM原参数对反电动势估算的影响进行分析,分析结果验证了该方法的理论可行性。利用MATLSB/Simulink进行仿真,并进行了针对性实验。实验结果表明,文中所提算法无须电角度补偿,在扰动条件下仍能对电机转子位置和速度进行良好地跟踪。     

The influence of the mobile phase pH and the stationary phase type on the selectivity tuning in high performance liquid chromatography nucleosides separation

Analysis of the modified nucleosides is particularly important in the medical area because of a possibility of cancerogenic processes studies. The aim of this work was to study the selectivity tuning of modified nucleosides through the investigations of interactions analyte (modified nucleoside) <==> stationary phase <==> mobile phase. A series of homemade stationary phases with different surface properties has been utilized. All of them contain various interaction sites such as: cholesterol (SG-CHOL); n-acylamide (SG-CHOL, SG-AP); aminopropyl (SG-CHOL, SG-AP, SG-NH2, SG-MIX); cyanopropyl, phenyl, octyl (SG-MIX), octadecyl (SG-MIX, SG-C18) and silanols localized on the silica gel surface of all packings. The attempt to predict the main interactions responsible for the retention between nucleosides and stationary phase ligands was done on the basis of the elemental analysis, and proportional part of an individual ligand bonded to silica surface results. In order to study the influence of different packing types on the analyzed nucleosides retention, the relationship between pH of the mobile phase buffer and the selectivity of a stationary phase was investigated.     

Stationary points on the aminomethanol potential energy surface

Summary In this work we study surface fitting equations for a rigid rotor model of aminomethanol. The energies were obtained from the GAUSSIAN88 package using 3-21G bases and fitted on a least square equation, thus generating a Fourier series expansion of the energy as a function of two dihedral angles. The dihedral angles chosen are those that represent rotation around the C-O and N-C axes in the first case, and rotation around C-O and inversion around the amino group in the second case. Results indicate that the hydroxyl hydrogen is subject to almost free rotation around the C-O axis. Further fully relaxed 6-31G* calculations were performed in order to qualify the results obtained for the rigid rotor model.