Novel shape and placement definitions with retention modeling for solid microfabricated pillar columns for CEC and HPLC

Abstract

A novel design approach for optimizing the shape of microfabricated pillar columns for LC is presented. 2-D flow simulations are performed with a focus on electrokinetically driven flow, in order to evaluate the performance of the new method. The proposed foil shape is compared with geometrical shapes known from the literature, for various arrangements. It yields a much more uniform velocity field distribution and a decrease in plate height values up to 25%. In addition to shape optimization, a new method for spatial arrangement of structures is presented. With the aim of conserving the hydrodynamic balance, the axial spacing of the pillars is adjusted according to the proposed equivalent width approach. When compared with a fixed interpillar spacing in all directions, it increases the flow uniformity and results in an 18% lower plate height. A new direct simulation approach is implemented to model both flow field and retention for solid microfabricated pillar structures in the 2-D domain. This model, which defines retention as inward/outward fluxes through the wall surfaces as first order reactions, enables monitoring of the time-dependent process and an evaluation of the parameters affecting performance. The meaning of the obtained results in a practical setting, with limitations in photolithography and microfabrication, will be highlighted.

Performance Evaluation of Different Design Alternatives for Microfabricated Nonporous Fused Silica Pillar Columns for Capillary Electrochromatography

“…As a result, the simulated linear velocities of the mobile phase for all design alternatives were the same and exhibited only a 1% decrease compared to an empty channel. 12 However, experimental measurements resulted in a higher decrease in mean flow velocities, for example, a 5% decrease for the foil with 0°and 20% for diamond, with respect to the empty channel. Being a streamlined body, optimized for minimizing the disturbances through the flow field in the axial direction, the foil shape with 0°tip angle yielded the highest mobility.…”

“…where H ji is the theoretical plate height determined between the interfaces i and j, σ 2 is the peak variance, t R is the retention time, and L ji is the distance between the interfaces i and j. independent parameters for geometry definitions, the differences in shapes did not result in a significant effect on the performance for such high aspect ratio (length/width) structures for the nonretained case, which is in agreement with our previous modeling study. 12 After calculating the plate height values for different mobile phase velocities, the results were fitted with the van Deemter equation, 18 which relates the plate height with the mobile phase velocity as follows:…”

“…Our theoretical study in the field of CEC on the optimization of the shape and positioning of the microfabricated column structures coupled with retention modeling for solid pillars was published in 2010. 12 A new geometry was introduced instead of using the basic geometrical shapes used by others, and its performance was compared with the ones from literature. In two-dimensional ideal conditions, the proposed foil shape yielded a moderate increase in performance (in terms of plate height) among the other alternatives.…”

“…Microchip Design and Layout. As mentioned in the introductory part of the paper, the same design configurations as in the previously published theoretical work 12 were evaluated in this experimental study. A unit cell, which was extracted from an infinitely long and wide microchannel, was selected as the domain of interest in the previous study.…”

On-Chip Step-Mixing in a T-Nanomixer for Liquid Chromatography in Extended-Nanochannels

“…Another way to achieve column miniaturization is the on-chip integration of micro and nanostructures of different shapes, which form a separation channel . Separation performance is known to correlate with the structure and uniformity of the stationary phase, and an on-chip 2-D network of porous pillars with optimized geometry provides separation impedance that is 10-fold lower than that of the best-packed HPLC columns. , Therefore, the future of miniaturized HPLC with high resolution lies with on-chip integrated nanostructures. In our extended-nanochromatography we use an open tubular-like nanochannel column with a femtoliter volume.…”