Generation-Collection Electrochemistry Inside a Rotating Droplet

In this work, we explore generation collection electrochemistry in a rotating droplet hydrodynamic system, where a 70 mu L droplet containing a redox active species (ferrocyanide) is sandwiched between an upper rotating rod and bottom nonmoving generator and collector planar electrodes. In such a system, we studied the effect of the counter electrode reaction on the recorded generator current, and the effect of the generator collector distance (ranging from 3 to ca. 500 mu m) on the collection efficiencies obtained at rotation rates ranging from 50 to 1100 rpm. We found that the counter electrode reaction competes with the collector reaction for the regeneration of the electroactive species; thus, collection efficiencies of 100% are probably impossible to obtain with this system geometry. We found that the collection efficiency increases with the droplet rotation rate and decreases with the generator-collector distance. The highest collection efficiency we obtained is 62% for the generator-collector distance of 3 mu m, which is more than two times higher than that for typical bulk experiments with a commercial rotating ring disk electrode. We show that the increased collection efficiency can be successfully used in epinephrine detection for filtering out signals from ascorbic acid and uric acid interferents.