Insight the role of electrolyte in electrokinetic stacking of targets by ion concentration polarization on a paper fluidic device

Charged components can be effectively separated and enriched based on ion concentration polarization (ICP) effect for sample clean up and enhancement of detection sensitivity in analytical chemistry. Concerning the role of electrolyte, current studies on electrokinetic stacking with ICP mainly focused on the ionic strength, and the knowledge about the type of supporting electrolyte (SE) is still poor. In this study, the significance of acid–base property of SE was systematically investigated based on an ICP interface established on a paper fluidic device with ion exchange membrane. Using colored ion probes for visualization of the effects, the ion depletion zone as the working area was applied for electrokinetic stacking. It has been shown that, besides the proper electroosmotic flow and ionic strength decided by neutral salt, the acid–base property of SE plays an important role for a successful stacking with ICP. The guideline for SE selection was proposed, and the mechanism was well explained by correlating the water dissociation effect and electric field/pH gradient (double gradients) at the ion depletion zone. This rule proposal is substantial for the design and operation of electrokinetic enrichment and separation of targeted species using ICP effect.