Impact of transversal vortices on the performance of open-tubular liquid chromatography

Open-Tubular Liquid Chromatography (OTLC) is currently limited by two shortcomings, namely the low ratio of adsorbing area to the channel volume and the large values of the Height Equivalent of the Theoretical Plate (HETP) due to Taylor-Aris dispersion. Previous work focusing on axial dispersion of nonadsorbing solutes showed how it is possible to tame the Taylor-Aris effect by inducing transversal velocity components acting alongside the main pressure-driven axial flow. We here analyze the impact of transversal flow on the separation resolution in OTLC, where simultaneous equilibrium adsorption at the channel walls is superimposed to the analyte transport in the mobile phase. A three-dimensional steady flow generated by the combination of a pressure-driven flow and an electroosmotically-induced transversal flow is used as case study. Flows geometries possessing regular and chaotic streamlines are created by axially-invariant and periodically-alternate arrangements of the electrodes along the channel walls, respectively. By enforcing Brenner's macrotransport approach, we predict the column length achieving a prescribed level of resolution as a function of the Péclet number and of the species affinity towards the stationary adsorbing phase. Results show that the presence of transversal flows can lower sensitively the dependence of the column length on the Péclet number. Flows possessing chaotic streamlines prove the most efficient choice at large eluent velocities and low values of the column adsorption constant.