50-Fold Reduction of Separation Time in Open-Channel Hydrodynamic Chromatography via Lateral Vortices

Abstract

Despite its relatively long history, open-channel hydrodynamic chromatography (OC-HDC) still represents a niche technique for determining the size distribution of particle suspensions. Practical limitations of this separation method ultimately arise from the low eluent velocity that is necessary to contain the adverse increase of analyte bandwidth caused by Taylor-Aris dispersion. Because of the micrometric size of the channel cross section, the low eluent velocity translates into order of pL-per-minute flow rates, which introduce a challenge for both the injection and the detection systems. In this article, we provide theoretical/numerical evidence illustrating how a sizable reduction of the Taylor-Aris effect can be obtained by triggering crosssectional vortices alongside the main pressure-driven axial flow. As a case study, we consider a square channel geometry where the lateral vortices are created by DC-induced electroosmosis. The analysis of particle separation is based on the classical excludedvolume macrotransport approach, which allows to derive the average particle velocity and the axial dispersion coefficient from the solution of two stationary advection-diffusion problems defined onto the channel cross section. We find that lateral vortices can enhance the separation efficiency quantitatively, e.g., by reducing the separation time of a two-species mixture by a 50-fold factor compared to standard OC-HDC.

C-Term Reduction in 3 μm Open-Tubular High-Aspect-Ratio Channels in AC-EOF Vortex Chromatography Operation

“…Also, the theoretical work of other groups , convincingly showed the favorable impact of lateral flow on dispersion under retained and unretained conditions. Very recently, a simulation study also predicted a large performance gain when enhancing lateral transport of particles (with an inherently small molecular diffusion coefficient) in the context of hydrodynamic chromatography, with an analysis time gain of a factor of 50, resulting from the induced lateral flow (particle mixture with dimensionless radii of 1:20, 1:40, and 1:80) . For the experimental approach, we recently superimposed a (small) lateral AC-operated electroosmotic flow (EOF) or acoustic flow , on an axially oriented pressure-driven flow and demonstrated that the C-term of low AR channels (AR ≤ 2) could be reduced up to a factor of 3, using channels with a critical dimension of 20 μm and above.…”

“…Very recently, a simulation study also predicted a large performance gain when enhancing lateral transport of particles (with an inherently small molecular diffusion coefficient) in the context of hydrodynamic chromatography, with an analysis time gain of a factor of 50, resulting from the induced lateral flow (particle mixture with dimensionless radii of 1:20, 1:40, and 1:80). 11 For the experimental approach, we recently superimposed a (small) lateral AC-operated electroosmotic flow (EOF) or acoustic flow 12,13 on an axially oriented pressure-driven flow and demonstrated that the C-term of low AR channels (AR ≤ 2) could be reduced up to a factor of 3, using channels with a critical dimension of 20 μm and above. In the present contribution, we fabricated and tested individual channels of which the critical dimension was scaled down to 5 μm (AR = 4.0) and subsequently to 3 μm (AR = 6.7) and we studied the influence of the driving force for the EOF (the laterally applied voltage) and the buffer salt concentration on dispersion of large molecules (dextran).…”

AC Electrothermal Effect Promotes Enhanced Solute Mixing in a Wavy Microchannel

“…According to recent experimental work, the AC electroosmotic flow can minimize Taylor–Aris dispersion even further by generating vortices in open-tubular microfluidic channels while subjected to an axial pressure gradient . In this microfluidic system, the use of DC-electroosmotic vortices increases the strength of axial flow and reduces the separation of two species by a factor of 50 . Furthermore, many biological liquids exhibit viscoelastic behavior.…”

“…36 In this microfluidic system, the use of DCelectroosmotic vortices increases the strength of axial flow and reduces the separation of two species by a factor of 50. 37 Furthermore, many biological liquids exhibit viscoelastic behavior. If the Weissenberg number for such liquids driven by electrically powered actuation exceeds a critical value, local electroelastic instability is permitted.…”