Surface diffusion and effective pore diffusion in reversed-phase liquid chromatography studied by molecular dynamics simulations

通过分子动力学模拟研究反相液相色谱中的表面扩散和有效孔扩散

• 批准号: 397067997
• 负责人: Professor Dr. Ulrich Tallarek
• 金额: --
• 依托单位: Fachgebiet Analytische Chemie und Radiochemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/397067997?language=en
• 关键词: Surface; diffusion; effective; pore; reversed

The project goal is to establish a consistent, molecular-level picture of surface diffusion and effective pore diffusion in reversed-phase liquid chromatography (RPLC), the most popular liquid chromatographic separation technique. Diffusion in and near the stationary phase is spatiotemporally resolved using molecular dynamics (MD) simulations in a model RPLC system. Pore-level diffusion is subsequently traced up to the macroscopic fixed-bed level using a hierarchical diffusion model, to allow for critical comparisons with chromatographic data. Small aromatic hydrocarbons like ethylbenzene and benzyl alcohol are used as representative analytes, which can be distinguished regarding their polarity and thus concentration, molecular orientation, and mobility in and near the RPLC stationary phase. They also partition to a varying degree into the hydrophobic alkyl chains of the chromatographic interface. This partitioning into the alkyl chains (i.e., into the bonded stationary phase), together with analyte adsorption onto the chains, forms the molecular basis for effective pore diffusion, analyte retention, and selectivity, as well as for nonlinear effects due to concentration overloading. These aspects are elaborated, while analyte (size, polarity) and mobile phase properties (composition of the water-acetonitrile mixture) are adjusted. Additionally investigated aspects are the polarity of the stationary phase (C18 vs. C8 chains as surface modification) and the pore geometry (planar vs. cylindrical). The MD simulations provide key data about local concentrations, residence times, diffusive mobilities, as well as data on a differential partitioning and adsorption on the pore level. They can rationalize the macroscopic, thus experimentally accessible transport dynamics and separation effects like retention and selectivity as well as the shape of adsorption isotherms, or even allow to predict these characteristics of (non)linear RPLC. The MD simulation-based effective pore diffusion coefficient (single-mesopore level) is combined with available physical reconstructions of mesopore and macropore spaces from hierarchically structured chromatographic beds. It allows us to analyze (through mass transport simulations based on a random-walk approach) effective diffusion in the interconnected mesopore space and, subsequently, effective diffusion at the macroscopic level of a macroporous-mesoporous chromatographic bed (e.g., a packing of mesoporous particles or a monolith). This hierarchical diffusion approach guarantees that relevant molecular details (stationary phase and analyte properties) and resulting phenomena (e.g., diffusion in and near the stationary phase; adsorption and partitioning under nonlinear conditions) are properly accounted for on the pore level, in the MD simulations, and can be morphologically traced up to the macroscopic field level, where the resulting data can challenge chromatographic experiments (and vice versa).

项目目标是在反相液相色谱法（RPLC）中建立一致的，分子级的图像，这是最流行的液态色谱分离技术。使用Model RPLC系统中的分子动力学（MD）模拟在固定相中和附近的扩散进行空间分辨。随后，使用层次扩散模型将孔隙级扩散追溯到宏观固定床水平，以允许与色谱数据进行关键的比较。小芳烃（如乙烯苯和苄醇）被用作代表性分析物，可以在其极性方面区分，从而在RPLC固定期内及其附近区分浓度，分子取向以及迁移率。它们还以不同的程度分配到色谱界面的疏水烷基链中。将这种分配到烷基链中（即进入键合的固定相），以及分析物吸附到链上，构成了有效孔扩散，分析物保留和选择性的分子基础，以及由于浓度过载而引起的非线性效应。这些方面是详细阐述的，而分析物（大小，极性）和流动相性特性（水 - 乙腈混合物的组成）进行了调整。另外，研究的方面是固定相的极性（C18 vs. C8链作为表面修饰）和孔的几何形状（平面与圆柱形）。 MD模拟提供了有关局部浓度，停留时间，扩散迁移率以及有关孔隙级别差分分配和吸附的数据的关键数据。它们可以合理化宏观，从而实验可访问的运输动力学和分离效应，例如保留和选择性以及吸附等温线的形状，甚至允许预测（非）线性RPLC的这些特征。基于MD仿真的有效孔扩散系数（单米孔水平）与来自层次结构化色谱床的中孔和大孔空间的可用物理重建相结合。它使我们能够在互连的中孔空间中分析（通过基于随机步行方法的质量传输模拟）有效扩散，然后，随后，在大孔孔色谱床的宏观水平上有效扩散（例如，中孔颗粒的包装或单岩）。这种层次扩散方法确保相关的分子细节（固定阶段和分析物特性）以及所产生的现象（例如，在固定阶段和接近固定阶段的扩散；在非线性条件下的吸附和分配）在孔内适当地解释了MD模拟的孔隙水平，并且可以在MD模拟中进行攻击，从而可以形式地传达了范围的实验，并在其中传达了一个范围的范围，并且可以将其传播到一个范围内，并且可以将其传播到一个范围内，并且可以将其传播到一个范围内，并且可以在范围内传达进一步的范围。反之亦然）。