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).

该项目的目标是在反相液相色谱 (RPLC)（最流行的液相色谱分离技术）中建立一致的表面扩散和有效孔扩散的分子水平图。使用模型 RPLC 系统中的分子动力学 (MD) 模拟，可以时空解析固定相内及其附近的扩散。随后使用分层扩散模型将孔隙水平扩散追溯到宏观固定床水平，以便与色谱数据进行关键比较。乙苯和苯甲醇等小芳香烃被用作代表性分析物，可以根据其极性来区分，从而根据 RPLC 固定相内和附近的浓度、分子取向和迁移率来区分。它们还不同程度地分配到色谱界面的疏水烷基链中。这种分配到烷基链（即键合的固定相）以及分析物吸附到链上，形成了有效的孔扩散、分析物保留和选择性以及由于浓度超载导致的非线性效应的分子基础。对这些方面进行了详细阐述，同时调整了分析物（尺寸、极性）和流动相特性（水-乙腈混合物的组成）。另外研究的方面是固定相的极性（C18 与 C8 链作为表面改性）和孔几何形状（平面与圆柱形）。 MD 模拟提供了有关局部浓度、停留时间、扩散迁移率的关键数据，以及有关孔隙水平上的差异分配和吸附的数据。它们可以使宏观的、因此可以通过实验获得的传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）合理化，甚至可以预测（非线性）线性 RPLC 的这些特征。基于 MD 模拟的有效孔扩散系数（单中孔水平）与分层结构色谱床中孔和大孔空间的可用物理重建相结合。它使我们能够（通过基于随机游走方法的传质模拟）分析互连介孔空间中的有效扩散，以及随后在大孔-介孔色谱床（例如介孔颗粒堆积）的宏观水平上的有效扩散或整体）。这种分层扩散方法保证了 MD 模拟中在孔隙水平上正确考虑了相关分子细节（固定相和分析物性质）和由此产生的现象（例如，固定相内和附近的扩散；非线性条件下的吸附和分配） ，并且可以在形态上追溯到宏观领域水平，其中产生的数据可以挑战色谱实验（反之亦然）。