Sample dispersion in isotachophoresis with Poiseuille counterflow

TL;DR

This paper investigates how Poiseuille counterflow in isotachophoresis causes significant sample dispersion, affecting resolution, and demonstrates that a simplified one-dimensional model can effectively predict this dispersion for better protocol simulation.

Contribution

It introduces a two-dimensional finite-volume model for ITP with counterflow and validates a simplified one-dimensional model for efficient dispersion prediction.

Findings

Poiseuille flow causes notable sample zone dispersion in ITP.

A one-dimensional Taylor-Aris-type model accurately predicts dispersion.

Simplified models enable rapid simulation of ITP with counterflow.

Abstract

A particular mode of isotachophoresis (ITP) employs a pressure-driven flow opposite to the sample electromigration direction in order to anchor a sample zone at a specific position along a channel or capillary. We investigate this situation using a two-dimensional finite-volume model based on the Nernst-Planck equation. The imposed Poiseuille flow profile leads to a significant dispersion of the sample zone. This effect is detrimental for the resolution in analytical applications of ITP. We investigate the impact of convective dispersion, characterized by the area-averaged width of a sample zone, for various values of the sample P\'{e}clet-number, as well as the relative mobilities of the sample and the adjacent electrolytes. A one-dimensional model for the area-averaged concentrations based on a Taylor-Aris-type effective axial diffusivity is shown to yield good agreement with the finite-volume calculations. This justifies the use of such simple models and opens the door for the rapid simulation of ITP protocols with Poiseuille counterflow.