基于随机扩散理论的气相色谱分离模拟

色谱分离过程中的粒子扩散问题是色谱动力学研究的基础,深入理解粒子的扩散行为对优化分离操作条件、提升色谱性能和开发新型色谱柱尤为关键.现有的模拟方法多集中于局部过程的热力学研究,而整体的扩散分离过程报道并不多见.为此,该文基于微尺度受限空间内随机扩散的方法,通过动态追踪粒子的运动轨迹,实现粒子在气相色谱开管柱内的扩散全过...     

基于随机扩散理论的色谱模拟辅助化学教学研究

为了满足当今教学的信息化发展趋势,本研究基于随机扩散理论建立了气相色谱仿真模型并开发了相关的计算模拟软件Stochastic Diffusion-Chroma。以混合组分分别在气相色谱填充柱和毛细管柱中的扩散分离模拟为例,探究了随机扩散理论模型在色谱理论教学和实验教学方面的应用。基于随机扩散理论的仿真教学改变了传统的教学模式,将学生较难理解的抽象色谱动力学基本理论转变为动态的具体形象,激发了学生的学习兴趣,提高教学质量。     

基于布朗棘轮的单通道分离体系的模拟研究

分子在微尺度受限空间内的扩散行为是微观化学的重要研究领域. 本文利用布朗棘轮效应构建了一种微型单通道分离器件模型, 并基于随机行走理论对其中分子的扩散分离运动进行了模拟研究, 阐明了该体系的分离机理并考察了不同条件对分子扩散分离运动的影响. 模拟结果表明, 通过调节驱动力对各组分粒子的作用周期, 可以控制粒子与分离通道两端势垒发生不同程度的相互作用, 从而在单分离通道内实现粒子向不同方向的有效分离. 同时, 也给出了利用该分离体系进行分离的组分粒子本身的扩散运动与受外力驱动运动的相对大小需满足的条件. 通过调整分离器件的结构参数, 可在实现最佳分离效果的同时节约时间成本. 本文提出的模拟方法对开发微型分离器件及优化操作参数等具有参考意义.     

基于分离粒子随机扩散理论的色谱模拟

为了对扩散分子的轨迹实施动态追踪与模拟, 深入理解分子扩散对色谱动力学的影响, 本文利用微尺度受限空间随机行走的模拟方法对色谱填充柱中的分子扩散过程进行了模拟. 重点考察了固定相的填充率、固定相的形状和柱长对色谱动力学行为的影响. 模拟结果表明短柱和大填充率具有较高的柱效; 在相同的密堆排列下, 固定相形状对分子扩散过程影响微弱; 待分离粒子的运动表现出微尺度空间限域的扩散特征, 但粒子的流动行为会随外部压力的增大而增加. 本论文提出的模拟方法对于发展高效能色谱, 开发新型分离技术等具有参考意义.     

液相制备吸附色谱流出峰对称性的若干影响因素

在色谱分离连续性方程和质量传递速率方程基础上,对色谱分离过程进行计算机模拟,定量分析了分离体系的热力学、动力学参数和操作条件对色谱流出峰形对称性的影响。结果表明,吸附相平衡关系、液固两相间的传质阻力及进料体积、进料浓度和流体线速等都将直接影响色谱流出峰形的对称性。流出峰形的不对称程度随着吸附等温线的非线性程度、液固两相间的传质阻力、流体线速、进料体积、进料浓度的增大而增大;在线性条件下,随着吸附剂吸附容量的减小而增大。     

Modification of a commercial chiral stationary phase influences on enantiomer separations using simulated moving bed chromatography

Chromatographic enantiomer separations using high-performance chromatography and the simulated moving bed (SMB) principle have become a practically useful method for obtaining optical isomers. The carbamate derivatives of amylose coated onto silica particles are very effective chiral stationary phases (CSPs). Several lots of Chiralpak AS, and its successor, Chiralpak AS-V, were compared by laser diffraction, microscopic imaging and pulse injections with increasing amounts of various racemates in order to determine the loading capacity and the competitive adsorption isotherms. Software simulations allowed to assess the possible effects due to the observed variations between the CSPs on the performance of a pilot SMB unit. The obtained results were verified by two multi-kilogram separations performed under current good manufacturing principles (cGMP) guidelines employing the two CSPs. The results of the two production runs are discussed in the light of the recently introduced "triangle theory" which allows to account for the overload conditions prevailing under preparative chromatographic conditions and to predict optimal operating conditions. Under optimized conditions the enantiomer separation of 1.4 kg racemate/kg stationary phase per day with purities >99.6% for the target enantiomer have been achieved.     

Robust design space development for HPLC analysis of five chemical components in Panax notoginseng saponins

The present work describes the systematic development of a robust, precise, and rapid reversed-phase liquid chromatography method for the simultaneous analysis of five chemical components in Panax notoginseng saponins (PNS) using quality by design (QbD). The method was developed in two main phases: screening and optimization. During the screening phase, the most suitable stationary phase, column temperature, and flow rate were identified, while the secondary influential parameters, such as the gradient slope, the initial concentration of acetonitrile, and the initial isocratic hold of the gradient elution system were fine-tuned in the later optimization phase. In this phase, a 17-run experiment was used to examine multifactorial effects of these parameters on the critical resolution, analysis time, and peak symmetry. The Monte Carlo simulation method was successfully used to build the chromatographic design space and the process capability index C_p was introduced to evaluate the robustness of the design space. At last, the verification experiment was performed within the working design space by the accuracy profile methodology and model was found to be accurate. A robust combination of separation conditions predicted in the design space was obtained with the gradient slope of 1.6% · min^?1, the initial concentration of acetonitrile of 20%, and the initial isocratic hold of 20 min, and the total analysis time was no more than 40 min. The results demonstrated that rapid separation of five components of PNS herbal extract could be achieved on the chromatographic column packed with narrow size particles at backpressures available in ordinary high performance liquid chromatography (HPLC) instruments.     

One-pot synthesis of pillar[5]quinone-amine polymer coated silica as stationary phase for high-performance liquid chromatography

To expand the application of pillararene in chromatographic separation, we designed and fabricated a pillar[5]quinone-amine polymer coated silica through quinone-amine reaction by facile one-pot synthesis method, which was applied as a stationary phase for high-performance liquid chromatography. Separation of hydrophobic compounds, hydrophilic compounds, halogenated aromatic compounds, and 11 aromatic positional isomers was achieved successfully in this stationary phase. Reverse-phase separation mode and hydrophilic-interaction separation mode were proved to exist, indicating the potential application of the mix-mode stationary phase. Studies of chromatographic retention behavior and molecular simulation showed that multiple interactions might play an important role in the separation process, including hydrophobic interaction, hydrogen-bonding interaction, aromatic π-π interaction, electron donor-acceptor interaction, and host-guest interaction. Column repeatability and stability were tested, which showed relative standard deviations of retention time less than 0.2% for continuous 11 injections, and the durability relative standard deviations of retention time were less than 0.91% after 90 days. This novel design strategy would broaden the application of pillararene-based covalent organic polymer in chromatography and separation science.     

双柱交替循环色谱分离甘露醇山梨醇过程

本文在非线性非平衡双柱循环色谱分离过程数学模型的基础上,进行了双柱交替循环色谱分离甘露醇山梨醇的实验,对模型进行了实验验证。结果表明：采用非线性非平衡双柱循环色谱模型计算的流出曲线与实验结果相吻合。计算机模拟的结果从理论上证明了对本实验体系采用双柱交替循环色谱分离模式比采用传统的色谱分离模式能获得更高的分离产率,产率随循环次数的增加而增加,使用双柱交替循环色谱分离操作模式获得的分离效率超过使用传统长色谱柱操作模式获得的分离效率。当轴向扩散比较严重、液固两相间的传质阻力较大,或者吸附的表观选择性系数较小时,采用双柱循环色谱模式比使用传统单柱色谱模式能获得更高的产率。     

High throughput liquid chromatography with sub-2 microm particles at high pressure and high temperature

In this study, ultra performance liquid chromatography (UPLC) using pressures up to 1,000 bar and columns packed with sub-2 microm particles has been combined with high temperature mobile phase conditions (up to 90 degrees C). By using high temperature ultra performance liquid chromatography (HT-UPLC), it is possible to drastically decrease the analysis time without loss in efficiency. The stability and chromatographic behavior of sub-2 microm particles were evaluated at high temperature and high pressure. The chromatographic support remained stable after 500 injections (equivalent to 7,500 column volumes) and plate height curves demonstrated the capability of HT-UPLC to obtain fast separations. For example, a separation of nine doping agents was performed in less than 1 min with sub-2 microm particles at 90 degrees C. Furthermore, a shorter column (30 mm length) was used and allowed a separation of eight pharmaceutical compounds in only 40s.     

Comparison of the mass transfer in totally porous and superficially porous stationary phases in liquid chromatography

The characterization of mass-transfer processes in a chromatographic column during a separation process is essential, since the influence of the mass-transfer kinetics on the shape of the chromatographic band profiles and on the efficiency of the separation is crucial. Several sources of mass transfer in a chromatographic bed have been identified and studied: the axial dispersion in the stream of mobile phase, the external mass-transfer resistance, intraparticle diffusion, and the kinetics of adsorption–desorption. We measured and compared the characteristics and performance of a new brand of shell particles and those of a conventional brand of totally porous silica particles. The shell stationary phase was made of 2.7-μm superficially porous particles (a 1.7-μm solid core is covered with a 0.5-μm-thick shell of porous silica). The other material consisted of totally porous particles of conventional 3.5-μm commercial silica. We measured the first and second central moments of the peaks of human insulin over a wide range of mobile phase velocities (from 0.02 to 1.3 mL/min) at 20°C. The plate height equations were constructed and the axial dispersion, external mass transfer, as well as the intraparticle diffusion coefficients were calculated for the two stationary phases.     

Computational chemical analysis of the retention of acidic drugs on a pentyl-bonded silica gel in reversed-phase liquid chromatography

A fast method to obtain a quantitative structure-retention relationship is required in chromatography for the rapid optimization of chromatographic separation conditions. Chromatographic data of acidic drugs are analyzed by a computational chemical method to simulate chromatographic simulation. The direct interaction between a model phase and a drug is calculated as an energy value using the molecular mechanics calculation of CAChe. Computational chemistry using a model adsorbent is a new method for quantitative analysis of retention in reversed-phase liquid chromatography. The correlation coefficient is 0.878 (n = 19) between the retention factors of acidic drugs and interaction energy values of the final structure (DeltaFS) between an acidic drug and model pentyl-bonded phase.     

Surface diffusion in reversed-phase liquid chromatography

More than 40 years ago, Giddings pointed out in “Dynamics of Chromatography” that surface diffusion should become an important research topic in the kinetics of chromatographic phenomena. However, few studies on surface diffusion in adsorbents used in chromatography were published since then. Most scientists use ordinary rate equations to study mass transfer kinetics in chromatography. They take no account of surface diffusion and overlook the significant contributions of this mass transfer process to chromatographic behavior and to column efficiency at high mobile phase flow rate. Only recently did the significance of surface diffusion in separation processes begin to be recognized in connection with the development of new techniques of fast flow, high efficiency chromatography. In this review, we revisit the reports on experimental data on surface diffusion and introduce a surface-restricted molecular diffusion model, derived as a first approximation for the mechanism of surface diffusion, on the basis of the absolute rate theory. We also explain how this model accounts for many intrinsic characteristics of surface diffusion that cannot properly be explained by the conventional models of surface diffusion.     

Improved liquid chromatographic separation of different proteins by designing functional surfaces of cattle bone-originated apatite

Spherical particles of cattle bone-originated hydroxyapatite (r-HAp) were prepared by dissolution-precipitation, spray-drying using a two fluid-nozzle apparatus, and subsequent heat treatment. The product had effective pore structures for liquid chromatographic separation of albumin, myoglobin, ribonuclease, lysozyme and cytochrome c. The activated surfaces of the r-HAp particles were easily prepared with desired proportions of P- and C-sites and appropriate acid-basic strength for selective protein adsorption by optimizing the synthesis conditions. Liquid chromatography columns packed with the particles exhibited high resolution and durability in protein separation, reflecting stable distribution of pore size.     

Hydrodynamic aspects of slurry packing processes in microcolumn liquid chromatography

A Stokesian dynamics computer simulation based method is presented for the estimation of the bed porosity of slurry-packed capillary liquid chromatography (LC) columns. A colloidally well-described reversed-phase stationary phase-slurry liquid suspension was used as a model system. The applied simulation method takes into account the velocity of the slurry and colloidal interaction forces, as well as inter-particle hydrodynamic interactions. The predicted bed porosities suggest that a lower slurry velocity leads to a denser packing structure due to the increased effect of colloidal repulsion effects. The results of the simulations were compared with the external porosity and chromatographic performance of capillary LC columns that were packed at different filtration and compaction pressures. However, the trends that were observed in the experimental results suggest that hydrodynamic packing parameters have no or little effect on the chromatographic performance of capillary LC columns. Within the experimental parameter window, the chromatographic performance and the column porosity were not influenced by the filtration and compaction pressure, nor by the duration of the compaction process.     

Pore network modelling: determination of the dynamic profiles of the pore diffusivity and its effect on column performance as the loading of the solute in the adsorbed phase varies with time

A three-dimensional pore network model for diffusion in porous adsorbent particles was employed in a dynamic adsorption model that simulates the adsorption of a solute in porous particles packed in a chromatographic column. The solution of the combined model yielded the dynamic profiles of the pore diffusion coefficient of beta-galactosidase along the radius of porous ion-exchange particles and along the length of the column as the loading of the adsorbate molecules on the surface of the pores occurred, and, the dynamic adsorptive capacity of the chromatographic column as a function of the design and operational parameters of the chromatographic system. The pore size distribution of the porous adsorbent particles and the chemistry of the adsorption sites were unchanged in the simulations. It was found that for a given column length the dynamic profiles of the pore diffusion coefficient were influenced by: (i) the superficial fluid velocity in the column, (ii) the diameter of the adsorbent particles and (iii) the pore connectivity of the porous structure of the adsorbent particles. The effect of the magnitude of the pore connectivity on the dynamic profiles of the pore diffusion coefficient increased as the diameter of the adsorbent particles and the superficial fluid velocity in the column increased. The dynamic adsorptive capacity of the column increased as: (a) the particle diameter and the superficial fluid velocity in the column decreased, and (b) the column length and the pore connectivity increased. In preparative chromatography, it is desirable to obtain high throughputs within acceptable pressure gradients, and this may require the employment of larger diameter adsorbent particles. In such a case, longer column lengths satisfying acceptable pressure gradients with adsorbent particles having higher pore connectivity values could provide high dynamic adsorptive capacities. An alternative chromatographic system could be comprised of a long column packed with large particles which have fractal pores (fractal particles) that have high pore connectivities and which allow high intraparticle diffusional and convective flow mass transfer rates providing high throughputs and high dynamic adsorptive capacities. If large scale monoliths could be made to be reproducible and operationally stable, they could also offer an alternative mode of operation that could provide high throughputs and high dynamic adsorptive capacities.     

Separation of structurally similar nocathiacin analogues by reversed phase chromatography

The complete separation of structurally similar compounds has been a challenge due mainly to their similarity on physical and chemical properties. In the present study, a simple and effective chromatographic method to separate and purify nocathiacin acid from its structural analogue nocathiacin I was developed. After evaluating mobile phase compositions on the retention characteristics by reversed phase high-performance liquid chromatography (HPLC), the elution order of nocathiacin I and nocathiacin acid was completely reversed, and the resolution value between the two analogues was improved, by varying pH value and ionic strength, to greater than 10 from merged peaks under initial conditions. In addition, a preparative isolation of nocathiacin acid was performed by reversed phase column chromatography under the guidance of the HPLC study. This chromatographic method resulted in an efficient process to obtain pure nocathiacin acid with a recovery rate of 83%. The present approach offers a new methodology for the separation of structurally closely related secondary metabolites.     

Modeling Gas Chromatography with a Specified Temperature Dependence of Henry’s Law Constant

A derivation of the chromatographic curve equation and kinetic mechanisms that determine the diffusion broadening of chromatographic peaks are considered in detail. Being combined with the theory of adsorption in the Henry region, this work has served as a basis for the development of the MOLCHROM program for modeling the gas chromatography process. An example demonstrating the adequacy of the program and its usefulness in selecting separation conditions for complex mixtures is given.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 7, 2005, pp. 723–728.Original Russian Text Copyright © 2005 by Prudkovskii.     

液液萃取结合分散固相萃取-液相色谱串联质谱检测食品包装纸中的4-氨基偶氮苯

采用高效液相色谱-串联质谱法（LC-MS/MS）快速测定食品包装纸中偶氮染料释放的4-氨基偶氮苯.试样在0.5 mol/L氢氧化钠溶液的碱性环境下,用连二亚硫酸钠还原试样中的偶氮染料,用甲基叔丁基醚反萃取还原裂解产生的4-氨基偶氮苯,经氮吹、甲醇复溶后,用液相色谱-串联质谱进行测定,内标法定量.方法优化了色谱分离、质谱、液液萃取和分散固相萃取等条件.最优化条件下方法的检出限为0.13 mg/kg,定量限为0.42 mg/kg,加标回收率在90%~95%之间（添加水平分别为1、10、30 mg/kg）,相对标准偏差小于5%.     

Optimisation & scale-up of affinity chromatography

When affinity chromatography is used on the large scale, economics dictate that the process must be optimised to ensure high throughputs and high adsorbent utilisation. The optimisation of an affinity chromatography process starts with the selection of both the ligand and matrix components of the affinity adsorbent. The relative merits of using highly selective ligands and small particle matrices in the development of high performance chromatography systems is discussed. Once the adsorbent has been chosen the parameters that characterise its interaction with the adsorbate must be characterised from small scale experiments. The method is illustrated in a series of experiments that show the influence of a number of factors involved in the preparation of immobilised monoclonal antibodies on the subsequent performance of the immunosorbents. These parameters together with computer simulations of the chromatography process can be used to design and optimise the operation of large scale systems. Attention has to be given to the optimisation of the adsorption, washing and elution phases of the process. Apart from initial process design, it is also necessary to optimise the chromatographic separation during the run. This involves the need to be able to measure the chromatographic performance in an on-line manner and a number of approaches to achieve this are described.