Millisecond Coulometry via Zeptoliter Droplet Collisions on an Ultramicroelectrode

Abstract

AbstractWe show that discrete collisions of zeptoliter emulsion droplets on an ultramicroelectrode (UME) can be used as individual controlled potential coulometry experiments, lasting between 100 and 500 milliseconds. By loading a highly hydrophobic toluene droplet with a hydrophobic analyte of interest and knowing the volume of the droplet to a high degree of precision, Faraday's Law can be employed to calculate the number of electrons passed during the electrolysis. Monodisperse (±15 % of the average size) emulsion systems were created by ultrasonication followed by filtering through a 200 nm porous filter. Discrete droplet collision events were observed in the amperometric i‐t curve. Each of these collisions are interpreted as individual coulometry experiments, implying that several bulk electrolyses can be carried out over the course of one collision experiment. Herein, we show calculations of the electron stoichiometry for the ferrocene oxidation reaction, which agrees well with the expected value of 1 electron. We further extend the methodology to more complicated systems, such as the oxidation of tetrathiafulvalene (TTF), tertiary aliphatic amines, such as tripropylamine (TPrA), and a 1,2‐diphenylhydrazine (DPH) molecule. This electroanalytical methodology allows for fast, nanoscale electrolysis in low dielectric media.