Potentiometric characterisation of a dual-stream electrochemical microfluidic device

Abstract

A microfluidic device is presented with offchip 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.

Pharmaceutical modulation of diffusion potentials at aqueous–aqueous boundaries under laminar flow conditions

“…The diffusion potential is established within milliseconds after the two streams come into contact [23]. In previous measurements [30], we investigated the influence of the liquid flow rates on the measured potential peaks. It was found that the height of the potential peaks did not depend on the experimentally accessible flow rates, only the peak width increased with decreasing flow rates, due to a longer residence time of the liquids in the microchannel at slower flow rates.…”

“…As described previously [30,32], the measured open circuit potential, j oc , is a combination of the diffusion potential, j d , and the potential difference between the electrodes, j e , caused by the difference in chloride concentrations in the opposing reservoirs.…”

“…The fabrication of the microfluidic chip was based on poly(dimethyl siloxane) (PDMS) soft lithography, as described in detail previously [30]. The chip (Fig.…”

“…Josserand et al [27,28] and Lagger et al [29] further investigated the use of diffusion potentials in microfluidics to act as a hydro-voltaic cell. Recently, we employed open-circuit potentials and diffusion potential measurements to characterize dual-stream microfluidic devices, which possessed electrolyte reservoirs on each side of the chip that were connected to the microfluidic channel by capillaries [30]. This enabled in situ measurement of potentials in the microfluidic cell using off-chip electrodes and hence simplified the fabrication procedure compared to a previous device we studied that employed integrated electrodes [31].…”

Several ways to simulate time dependent liquid junction potentials by finite differences

“…It could be a membrane between two well stirred solutions. Experimentally, the situation of a watery boundary can also be be realised in microchannels, involving dual-stream laminar flow of two aqueous solutions along each other carrying different electrolyte salts at various concentrations [18][19][20][21][22] forming a flowing junction [17]. potential using the Henderson equation [20] and numerical solutions of the Nernst-Planck equation [21,22] and the measured open-cicuit potentials has been found.…”