|M.Sc Student||Ganor Nethanel|
|Subject||Diffusion Dependent Focusing Regimes in Peak Mode|
|Department||Department of Mechanical Engineering||Supervisor||ASSOCIATE PROF. Moran Bercovici|
|Full Thesis text|
Isotachophoresis (ITP) is an established electrophoretic technique used for separation and preconcentration of ionic species based on their effective electrophoretic mobility. In ITP, sample ions are focused under an electric field between a high mobility leading electrolyte (LE) and a low mobility trailing electrolyte (TE). The method allows for a significant increase in concentration, and is useful in a wide range of chemical and biochemical applications, including drug discovery, disease diagnostics, genetics, and environmental monitoring.
In counterflow ITP, an adverse pressure gradient is used to stop the ITP interface in place allowing longer accumulation time. It is particularly important in the use of ITP for acceleration of reactions, where holding the highly concentrated zone over long durations is of key importance. To the best of our knowledge, despite nearly a century of research into ITP, understanding of sample focusing in counterflow ITP is still lacking, and there are currently no models capable of predicting sample distribution and peak concentrations under such conditions.
In this work, we present an analytical, numerical and experimental study of pressure driven counterflow isotachophoresis. We study the Nernst-Planck equations in the axi‑symmetric and radially-dependent case, in the leading order of negligible body forces. We provide a simple model that describes the ITP interface shape for both Couette- and Poiseuille-type counterflows, and an asymptotic model which captures two distinct sample focusing regimes of peak mode ITP. We validate the existence of these regimes using numerical simulations, and map the conditions under which each of the focal regions dominates. We show numerically and experimentally that while pressure driven flow is typically considered to reduce peak concentrations, certain regimes allow a net gain in analyte concentration over the non-dispersed case. Finally, we experimentally demonstrate that co-focusing species may follow different focusing regimes and separate in the radial direction, perpendicular to the flow direction.