Advantages of Perfectly Ordered 2-D Porous Pillar Arrays over Packed Bed Columns for LC Separations:  A Theoretical Analysis

Abstract

A series of theoretical calculations is presented to quantify the gain in LC separation efficiency that can be expected if the traditionally used packed bed columns were replaced by columns with a perfectly ordered flow-through pore network. It is shown that a perfectly ordered 2-D array of porous cylindrical pillars could yield reduced plate heights as small as h = 0.65 (for k' ' = 0.75) to h = 0.85 (for k' ' = 2) and separation impedances as small as E = 200 (for k' ' = 0.75) to E = 300 (for k' ' = 2) without having to compromise on the porosity (epsilon = 0.4) and the retention capacity of the packed bed of spheres. Fitting the calculated van Deemter plots with Knox's equation especially shows a strong decrease of the A-term contribution, hence confirming that the improved column performance indeed stems from the increased homogeneity of the packing. The presented results, hence, provide a clear quantitative support for Knox's recent argumentation that the use of more uniform beds could greatly enhance the efficiency of pressure-driven LC.

The promise of nanotechnology for separation devices – from a top‐down approach to nature‐inspired separation devices

“…He mentioned micromachining of the column packing as one of the possible approaches to solve this problem. More recent calculations by Gzil et al [4] indeed showed that a perfectly ordered 2-D pillar array is expected to have a separation performance which is about ten times better than the best packed column. In 1998, He and Regnier [5] had already shown the first microfluidic structures with micromachined pillar arrays instead of conventional packing (Fig.…”

“…For more simple separations that require fewer plates however they are less efficient than the conventional columns packed with spherical particles [7]. The ultimate role of micro-and nanomachining could be to tailor external porosity and packing geometry to the separation problem at hand while at the same time maintaining mass loadability by using an internally porous column material [4].…”

Pillar‐structured microchannels for on‐chip liquid chromatography: Evaluation of the permeability and separation performance

“…The issue of dispersion in structured (micro) channels was tackled by a computational approach by Desmet's group [5]. They performed fluidic-dynamic simulations to study band dispersion in 2-D microchannels structured with cylindrical pillars.…”

Modeling the effect of species retention on the band broadening in perfectly ordered silica monolithic column mimics with variable external porosity and intra‐skeleton diffusivity

“…Besides the effect of D skel , different degrees of adsorptive species retention (quantified by the zone retention factor k99) have been considered as well. To achieve this, a second UDF was written to subject the species present in the porous skeleton zone to an adsorptive reaction with equilibrium constant K. The details of this UDF are described elsewhere [46]. The relation between K and the whole-skeleton-based K p is given by:…”