Waters Corporation, Instrument/Core Research/Fundamental, 34 Maple Street, Milford, MA, 01757, USA.
Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, Marburg 35032, Germany.
J Chromatogr A. 2020 Aug 16;1625:461325. doi: 10.1016/j.chroma.2020.461325. Epub 2020 Jun 10.
We derive a model of band broadening in multiple-open-tubular columns enabling transverse diffusion (MOTTD). In MOTTD columns, the flow channels are straight, parallel, cylindrical tubes arranged in a hexagonal compact array. A mesoporous material or stationary phase (130 Å bridged-ethyl hybrid (BEH) silica support) is filling the volume between the flow channels. The model is based on Giddings' random-walk theory of non-equilibrium chromatography. It is calibrated for the unknown configuration factor, q, related to the specific geometry of the stationary phase in MOTTD columns. q values are found based on the best fit of the model to simulated dispersion data obtained by the lattice-Boltzmann method for modelling fluid flow and a random-walk particle-tracking technique to address advective-diffusive transport of the analytes. For the model calibration, simulations are performed for different ratios, ρ, of the average inner diameter of the flow channels to their closest center-to-center distance under retained and non-retained conditions. The model is successfully validated (average relative errors below 10%) under both retained and non-retained conditions. For the same column format (4.6 mm i.d. × 150 mm), external porosity, zone retention factor, and relative standard deviation of the distribution of the inner diameters of the flow channels, the derived model reveals the intrinsic advantage of MOTTD columns (center-to-center distance between flow channels of 5 µm and ρ = 0.62) over a conventional column packed with 5 µm 130 Å BEH silica particles and the same multiple porous-layer open-tubular column (MPLOT) disabling transverse dispersion. MOTTD columns are weakly affected by the polydispersity of the inner diameter of the flow channels. Provided MOTTD columns could be prepared at a small feature size of 5 µm or less, they are expected to deliver a significant improvement in column technology relative to current particulate and silica monolithic columns.
我们推导出了一种适用于多通管柱（MOTTD）的带宽展宽模型，该模型可以考虑横向扩散。在 MOTTD 柱中，流道是直的、平行的、圆柱形的，排列成六边形紧凑的阵列。中孔材料或固定相（130Å 桥联乙基杂化（BEH）硅胶载体）填充在流道之间的体积中。该模型基于吉丁斯（Giddings）关于非平衡色谱的随机行走理论。它是根据未知的配置因子 q 进行校准的，q 与 MOTTD 柱中固定相的特定几何形状有关。q 值是基于模型对通过格子玻尔兹曼方法模拟的流体流动得到的模拟分散数据的最佳拟合，以及使用随机行走粒子跟踪技术解决分析物的对流扩散输运而得到的。对于模型校准，在保留和非保留条件下，模拟了不同的平均流道内径与最接近的中心到中心距离之比 ρ。该模型在保留和非保留条件下均得到了成功验证（平均相对误差低于 10%）。对于相同的柱格式（4.6mm i.d.×150mm）、外部孔隙率、区保留因子和流道内径分布的相对标准偏差，所推导的模型揭示了 MOTTD 柱（流道中心到中心距离为 5μm，ρ=0.62）相对于填充有 5μm 130Å BEH 硅胶颗粒的常规柱和具有相同的多微孔层开管柱（MPLOT）的固有优势，后者无法抑制横向扩散。MOTTD 柱对流道内径的多分散性的影响较弱。如果 MOTTD 柱可以在 5μm 或更小的小特征尺寸下制备，那么与当前的颗粒和硅胶整体柱相比，它们有望在柱技术方面取得显著进步。
