An electrochemical time-of-flight technique with galvanostatic generation and potentiometric sensing

A variation of an electrochemical time-of-flight (ETOF) technique is described and illustrated with the test cases involving electrochemically generated Ag+ and H+ ions in aqueous solutions of different viscosity and ionic strength. Similar to the earlier ETOF methods, the new ETOF technique also relies on photolithographically fabricated microelectrode devices. It uses a constant current (rather than potentiostatic) mode of generation of redox species and, unlike earlier approaches, it uses potentiometric (rather than amperometric) monitoring of the rates of their diffusion to the sensor microelectrode. The unknown D-values can be obtained by direct comparison between the experimentally obtained and digitally simulated E vs t transients. Digital simulations were based on simple hemi-cylindrical diffusion between the microband generator modeled as a hemi-cylinder and sensor microband electrode assumed to be infinitesimally small. This model approximates well the experimental results as long as the spacing between the two microband electrodes is approximately equal to or greater than twice their width. Discrepancies between theory and experiment may also arise due to the double-layer charging of the sensor ∣ solution interface, and migration effects.