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

Abstract

An experimental study comparing the performance of different designs for microfabricated column structures for microchip capillary electrochromatography is presented. The work is a follow-up to our previously published modeling and simulation study on the same topic. Experiments were performed using fused silica microchips with and without octadecyltrimethoxysilane coating for nonretained and retained modes of operation, respectively. Showing the same trends as the modeling results, the foil shape produces a significant decrease in plate height with an increase of around 15% in mobile phase velocity in nonretained measurements of Coumarin 480 (C480). Measured plate heights at 1 kV/cm applied electric field were 0.77, 1.33, and 1.42 μm for foil, diamond, and hexagon, respectively. Chromatographic runs of C480 yielded minimal plate height values of 1.85 and 3.28 μm for foil and diamond, respectively. The optimization of the shape and placement of the structures appeared to have a considerable impact on the achievable performance.

Bulk Micromachining of Si by Metal‐assisted Chemical Etching

“…With these all optimized conditions and methods, such as metal type and morphology, etchant concentration, etching bath change, and ultrasonic treatment, Figure e,h show results for capillary electrochromatography (CEC) pattern fabricated with the present method. The feature widths range from 1.2 mm down to ∼3 μm, due to bifurcating design of the pattern.…”

“…Further, it should be noted that the etch depth in Figure 5 c,d is ≈150 µm, showing that the present method can also be applied to the production of thin Si slabs by chemical etching, which might be very useful in Si solar cells (e.g., sliver cell [ 32 ] over large area at a lower cost). With these all optimized conditions and methods, such as metal type and morphology, etchant concentration, etching bath change, and ultrasonic treatment, Figure 5 e,h show results for capillary electrochromatography (CEC) pattern [ 33 ] fabricated with the present method. The feature widths range from 1.2 mm down to ∼3 µm, due to bifurcating design of the pattern.…”

Induced hydraulic pumping via integrated submicrometer cylindrical glass capillaries

“…The exponent n is a variable chosen here to obtain the best fit. The encounter of a negative A value has been recently reported and discussed by Sukas et al for which the authors concluded that forcing the A term to be independent of the linear velocity is an oversimplification that leads to the loss of data [48]. The reduced forms are given as: Table 1.…”

Methods to determine the kinetic performance limit of contemporary chromatographic techniques

“…Although the majority of the publications regarding the kinetic plot method relate to RPLC in normal of narrow bore packed bed columns, it has also been applied for chiral analysis [32–35], size‐exclusion chromatography (SEC) [14,36–39], comparison of packed columns with monolithic columns, and optimization of the latter's synthesis [16,40–46], to study the advantages of high temperature LC [47–48], performance of HILIC versus RPLC [49–50], microbore [51–52], open tubular [45,53,54], and pillar array columns [55–59], or to study the effect of the analyte on the kinetic performance limits [60–61]. In these cases, no significant changes to the method are required to establish the kinetic performance limits.…”

“…For electro‐driven separations, e.g. CEC, the (maximum) pressure can simply be replaced by the (maximum) voltage (ΔV (max) ) and the column permeability can be replaced by the electro‐osmotic flow mobility μ EOF , yielding the following two expressions: [46,54,58–59,67]: …”