Counterflow Isotachophoresis of Pyronin Y in a PMMA Microchip

Isotachophoresis (ITP) of pyronin Y, a cationic dye we use as a simulant and a marker in ƒ-element ITP, is performed in a 150 mm × 20 mm × 23 cm (width × depth× length) serpentine poly(methyl methacrylate) microchip in the presence of a counterflow. The concentrated zone of pyronin Y is detected using a commercial Capacitively Coupled Contactless Conductivity Detector (C4D) as it migrates through the channel toward the cathode. A hydrodynamic counterflow generated by a reservoir height difference produces stationary ITP zones, increasing the effective separation length of the channel. Formation of a stationary zone allows us to load more solute onto the chip, to use shorter channels and it provides more time for the ITP zones to form, leading to better resolution between the zones. A 2D simulation (COMSOL Multiphysics v5.1) of ITP in a serpentine channel shows the impact of counterflow dispersion on the performance of the microchip.