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...     

以金属有机骨架材料ZIF-8为固定相的硅基微气相色谱柱

基于微机电技术制备了一种含有椭圆微柱阵列的半填充柱; 采用水热法合成了一种金属有机骨架材料ZIF-8, 将其涂敷在微色谱柱的微沟道内壁上作为固定相. 在30 ℃恒温下对芯片的分离性能进行了测试, 结果表明, 以ZIF-8为固定相的微色谱柱可以在75 s内实现甲烷、 乙烷和丙烷(C1~C3)的基线分离, 其中甲烷-乙烷的分离度达到了2.23, 与以介孔硅为固定相的微色谱柱相比提高了99%; 甲烷、 乙烷的峰面积以及甲烷-乙烷分离度重复性的相对标准偏差均小于3%. 以上结果表明, 以ZIF-8为固定相的微色谱柱在针对油田气实时分离的便携式微色谱系统中具有广泛的应用前景.     

气相色谱中粒子运动行为的随机行走模拟

本文应用随机行走这一理论模型对气相填充柱色谱进行了研究。随机行走的处理方式是重点关注分子的运动行为,而忽略掉那些与色谱动力学关系较小的因素。模拟结果表明,在低温时分子的自主运动是扩散行为,当温度升高分子则带有了明显的流动行为。在此基础之上,对温度和压力这些影响分子运动行为的外部因素也进行了考察。同时进行了相对应的气相色谱实验,模拟得出了和实际实验相一致的结果。由于实际实验操作条件的限制,模拟结果给出了一个更宽泛的应用区间。     

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.     

高效金属有机骨架气相色谱固定相的理性设计北大核心CSCD

金属有机骨架材料(MOFs)由金属离子或金属簇与有机配体组装而成,其中多变的金属中心和有机配体使其具有高度可调性,这为调控高效气相色谱分离性能奠定了良好的结构基础。热力学作用力是描述分析物与固定相相互作用的基本指标,保留因子、麦氏常数、焓变与熵变等热力学值可以反映热力学作用力的相对大小。在微观层面上,可以通过设计MOFs孔隙内的多元作用力以开展热力学性质的研究,如设计金属亲和性、π-π相互作用、极性、手性位点等,这些热力学作用力可为分离具有微小差异的分析物提供有利环境。在动力学方面,MOFs的孔径大小与形状、颗粒尺寸、堆积模式对分析物的动力学扩散速率有着重要的影响,从改善分析物的动力学扩散角度出发,通过选择合适的孔径尺寸与形状、降低MOFs的颗粒尺寸、调控MOFs的堆积模式等手段,均可以提高气相色谱固定相的分离性能。根据色谱动力学统一方程和范蒂姆特方程计算扩散系数、理论塔板高度等动力学值,可有效评价色谱峰峰形和色谱柱柱效。在分离过程中,分析物的热力学作用力和动力学效应是协同作用的,且缺一不可。因此,本文从热力学与动力学两个角度提出了构建高效MOFs气相色谱固定相的设计思路,希望能为相关领域的研究提供一定帮助。     

二氢麦角碱在极性嵌入反相色谱固定相上的分离行为

二氢麦角碱的4种组分具有不同的药效特性,需适当的分析方法对其在不同剂型药品中的含量进行分析.传统液相色谱方法使用强碱性流动相,严重腐蚀硅胶基质色谱填料,影响色谱柱寿命.合成了极性嵌入反相固定相--C18酰胺固定相,并在中性流动相条件下分离4种组分.考察了流动相组成和pH对二氢麦角碱在C18酰胺固定相上保留行为的影响.在150 mm×4.6 mm I.D.的C18酰胺色谱柱上,流动相为乙腈-20 mmol/L Na2HPO4(30:70,V/V,pH 7.0)的条件下实现了4种组分的基线分离.与传统方法相比,极性嵌入反相固定相可以有效的改善碱性化合物的分离特性和大幅度地延长色谱柱的使用寿命.     

良溶剂中环形高分子单链的结构与动力学性质的模拟研究

本文采用多粒子碰撞动力学与分子动力学耦合的模拟方法研究了环形高分子单链在良溶剂中的静态与动态性质,并与线形分子进行了对比.研究发现,环形高分子链内粒子之间的平均距离小于线形链,即粒子排列得更加紧密;相应的均方回转半径也小于线形链,线形链与环形链的均方回转半径的比值为1.77;同时,环形链扩散的速度也比线形链快,两者比值为1.10.模拟结果揭示了扩散行为是排斥体积作用和流体力学相互作用耦合的结果,在扩散过程中,流体力学相互作用消减了排斥体积作用对扩散行为的贡献.此外,通过对有和没有流体力学相互作用的多粒子碰撞动力学得到的结果作对比,研究了流体力学相互作用对高分子静态和动态行为的影响,结果表明,流体力学相互作用使高分子链在极稀溶液中的扩散速度变快.     

亲水作用毛细管电色谱柱的研究进展

亲水作用毛细管电色谱是当前微分离技术的研究热点之一,其固定相的研究受到了广泛的关注。本文介绍了亲水作用毛细管电色谱开管柱、填充柱和整体柱的研究进展,重点对近年来发展的亲水作用电色谱整体柱的制备技术进行了系统阐述。引用文献68篇。     

基于随机行走扩散模型的气相色谱分离模拟

利用粒子在受限空间内随机行走的扩散理论,构建了气相色谱毛细管柱分离的仿真模型,系统地考察了各模拟参数对粒子在色谱柱内的碰撞情况和峰宽的影响。模拟结果表明随机速度和时间步长的增加以及载气流速的降低均会加剧粒子碰撞和色谱峰展宽,而相互作用虽与碰撞行为无关,但峰宽会随着相互作用的增加而显著增大。模拟结果证实了该模型与色谱基本理论的一致性。     

亚微米中孔SBA-15 棒状固定相在毛细管电色谱分离中的应用(英文)

采用中孔SBA-15棒状硅胶颗粒填充毛细管柱用于毛细管电色谱(CEC)分离。这一亚微米材料直径为400 nm并具有沿相同方向伸展的高度有序、均一的圆柱形中孔。棒状的特殊形态使得填充柱的通透性良好,简化了尺寸微小的CEC柱的填充过程。修饰后的棒状SBA-15填充毛细管柱成功应用于反相和离子交换电色谱分离非极性和极性样品,获得了较高柱效(140000理论塔板/m)。流速3.2cm/min时获得最低理论塔板高度为7.1 mm。范迪米特曲线说明了SBA-15孔结构的传质阻力特征。分别以芳香酸、人参、天麻提取物为样品,对亚微米固定相毛细管电色谱柱加以评价。该固定相显示出了较高的分离能力,为纳米材料在色谱固定相中的应用提供了一个新的思路。     

Theoretical simulation of chromatographic separation based on random diffusion in the restricted space

The diffusion behavior of particles in the chromatography is a fundamental issue of chromatographic dynamics. The understanding of the diffusion behaviors is particularly critical to optimize the operation conditions, improve the chromatographic performance and design a new separation device. Many of the present simulations focus on chromatographic thermodynamics, and very few aim at the overall diffusion and separation process. In order to dynamically trace the trajectory of the diffusing particles and to perform simulations of the whole chromatographic process, we have developed a model based on the framework of random walk in the restricted space and performed the simulation of a single particle diffusion in the gas chromatography. The simulation parameters were determined by comparing with the experimental data. The elution profiles of n-alkanes under different flow rates were accurately simulated with the method. The results show that the relative difference between the measures and the simulations are less than 2% and 10% for the retention time and the peak width, respectively. The simulation method shows great significance for the optimization of separation conditions and the development of novel technologies of chromatographic separation.     

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。     

A cellular automata model of chromatography

Dynamic models of the behavior of solvent and solute molecules can be made using cellular automata. A chromatographic column was represented by use of a cellular automata grid of 43 x 200 spaces. Solvent (mobile phase), solute and stationary phase cells were designated to simulate the chromatographic situation. The movements of solute and solvent cells down the grid were monitored for different numbers of iterations, different flow rates and different affinities of the solutes for the stationary phase and the solvent for itself. The cellular automata dynamics were successfully able to model expected chromatographic behavior except in a few cases where the number of cells was not large enough to provide an average value reflective of the molecular situation.     

Retention behavior of basic compounds on alkylphosphonate-modified magnesia-zirconia composite stationary phase in RPHPLC

Summary The chromatographic properties of an alkylphosphonate-modified magnesia-zirconia composite stationary phase have been investigated by reversed-phase high-performance liquid chromatography with basic compounds as probes. The influence of organic modifier composition and mobile phase pH was studied. The new stationary phase, similar to a silica-based reversed-phase stationary phase, has hydrophobic properties, but greater pH stability. Use of the phase results in more symmetric peaks for basic compounds. A possible mechanism of retention of basic solutes on the new stationary phase is discussed. The chromatographic behavior of the basic solutes depends mainly on hydrophobic interactions between the solutes and the hydrophobic moiety of the stationary phase. Br?nsted acidic and basic sites on the surface of the new stationary phase play an important role in the retention of ionized solutes by ion-exchange interaction. Promising separations of some basic compounds have been achieved by use of methanolic TRIS buffer, pH 10.0, as the mobile phase.     

电色谱塔板高度方程的推导

比较了电色谱与高效液相色谱在动力学过程方面的异同。从热传导方程出发导出在有源无限长均匀圆柱体内温度场分布函数及组分移动速度径向分布函数,进而导出了温度场导致谱带弥散的弥散系数Ｄ热。提出了较全面地反映电色谱动力学过程的塔板高度方程,从而为改进柱型、选择电色谱分离条件提供了理论参考。     

十二烷基键合氧化锆固定相的制备与性能评价

以自制5μm球形氧化锆为基质，制备了十二烷基键合氧化锆HPLC固定相，考察了正烷基取代苯、稠环芳烃、苯胺及吡啶衍生物、苯酚和硝基苯酚异构体等不同性质化合物在固定相上的保留行为，并与十二烷基键合硅胶固定相进行了比较。结果表明：中性和碱性化合物在固定相上主要为反相色谱保留机理；酸性化合物在固定相上以反相色谱保留机理为主，但是氧化锆表面的Lewis酸性中心对溶质也存在一定程度吸附作用，导致色谱峰拖尾。     

Dynamic coating ion-exchange chromatography of cations on an octadecyl-bonded silica stationary phase

It was found that common cations (Na+, NH4+, K+, Mg2+ and Ca2+) could be strongly retained on an ODS stationary phase when aqueous solutions of carboxylic acids were used as eluents. The chromatographic conditions used in this work were the same as in common cation-exchange chromatography on a cation-exchange resin and the retention behavior of the above-mentioned cations on the ODS column was quite similar to that on a cation-exchange column. The retention behavior and mechanism have been investigated using a number of carboxylic acids as eluents. The retention mechanism of the cations in these experiments was considered to be a dynamic coating ion-exchange mechanism. The carboxylic acids in the mobile phase were coated onto the surface of the ODS stationary phase and formed a dynamic carboxylic acid functional layer which could act like the functional group layer of a carboxylic group cation exchanger.     

Thermodynamic description of retention mechanism in liquid chromatography

The chemical and physical properties of the stationary and the mobile phase determine the retention and selectivity of the separated molecules in chromatographic process. It should explain the specific and non-specific interactions in the chromatographic system. Special emphasis should be placed on column selection through the adequate choice of column dimensions (diameter and length) and the type of stationary phase with required parameters, which contributes the system effectiveness. However, column effectiveness is unable to guarantee a satisfactory level of substance separation. For this reason, the interactions between the analyte, the stationary and the mobile phase need to be investigated to determine the retention factors of the separated substances and the optimal parameters of the chromatographic system. According to the principles of thermodynamics, in particular molecular interactions, the chromatographic process has to be carried out with a high level of control. This work can be treated a brief tutorial devoted to thermodynamics of liquid chromatography process with a special emphasis on molecular interactions between analyte species and the components of the mobile and stationary phases.     

Preparation of imidazole-functionalized silica by surface-initiated atom transfer radical polymerization and its application for hydrophilic interaction chromatography

A novel imidazole-functionalized stationary phase for hydrophilic interaction chromatography (HILIC) was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP). 1-Vinylimidazole as a monomer was polymerized on the surface of initiator-immobilized silica by SI-ATRP using CuCl and 2,2'-bipyridyl as a catalyst. The graft chain length and polymer grafting density were controlled by varying the ratio of monomer to initiator. The resulting materials were characterized by elemental analysis and thermogravimetric analysis. Then, high-performance liquid chromatography separation of eight nucleobases/nucleosides was performed on the imidazole-functionalized chromatographic column in HILIC mode. The effects of mobile phase composition, buffer pH, and column temperature on the separation of nucleobases/nucleosides were investigated, and the retention mechanisms were studied. Chromatographic parameters were calculated, and the results showed that surface adsorption through hydrogen bonding and electrostatic interaction dominated the retention behavior of the solutes in HILIC mode. Lastly, the stationary phase was successfully used to determine the nucleobases and nucleosides from Cordyceps militaris.