Potentiometric characterisation of a dual-stream electrochemical microfluidic device

Abstract

A microfluidic device is presented with off-chip electrodes residing in a reservoir and connected via micro-capillaries to the Y-shaped microfluidic channel. The device is tested by potentiometric measurements involving dual-stream laminar flow of two aqueous solutions carrying different electrolytes at various concentrations. Open circuit potentials are measured for a series of solutions of alkali metal chlorides and tetraalkylammonium chlorides as well as for dilute hydrochloric acid. The open circuit potential for the microfluidic chip was calculated by taking into account the diffusion potential at finite ionic strength as well as the potential difference introduced by the reference electrode system. The liquid junction potential developed at the boundary of the co-flowing aqueous solutions may be manipulated to have greater or lesser relative contributions to the measured open circuit potential based on use of electrolyte salts having cation and anion pairs of similar or dissimilar mobilities in solution. A reasonable agreement between theoretical and experimental values of the open circuit potential is observed for these situations. The results show that simple microfluidic structures possess a rich environment for exploration and application of the solution chemistry of ions.