(504j) Influence of Transversal Flows in Open-Tubular Liquid Chromatography (OTLC) and Hydrodynamic Chromatography (OTHDC)

Open Tubular Liquid Chromatography (OTLC) and Open Tubular Hydrodynamic Chromatography (OTHDC) are microfluidics assisted techniques for separating adsorbable solutes and suspended colloids, respectively. OTLC can be used to separate proteins, peptides, or amino acids, whereas OTHDC can be employed to separate particles in the range between tens nanometers to a few micrometers e.g., gold/silver nanoparticles, DNA fragments, or polymer suspensions. Both OTLC and OTHDC use open channels whose characteristic cross-sectional dimension ranges between 1-30 μm. Owing to the micrometric size of the channel cross-section, the Reynolds number is order unity or below which implies that the eluent flow satisfies the Stokes regime. In these conditions, both separation techniques represent a miniaturized alternative to packed LC and HDC columns. The separation efficiency of both methods is currently limited by two shortcomings: the low selectivity and the large values of the Height Equivalent of the Theoretical Plate (HETP) due to Taylor-Aris dispersion. We here show how the interplay between the pressure-driven flow and DC-induced electroosmotic transversal flows (possibly yielding chaotic advection) significantly reduces axial dispersion and thus the analyte bandwidth. In OTLC, the containment of the axial dispersion is due to the decreased transversal mixing time, hence, the highest separation performances are found in the case of the chaotic flow. In OTHDC, on the contrary, the lower values of axial dispersion are due to the localization effects of the finite-sized particles in the region characterized by the lower axial velocity gradients. For this reason, axially invariant (non-chaotic) flows perform better than those triggering chaotic advection. Brenner’s macro transport theory is here used to compute the effective parameters and estimate the separation efficiency.