Millisecond Coulometry via Zeptoliter Droplet Collisions on an Ultramicroelectrode

Controlled potential coulometry is a powerful tool in electroanalysis due to its ability to directly derive the quantity or electron stoichiometry of a substance without use of a calibration curve [1]. The technique has also been employed for mechanistic considerations; however, the general long experimental times (minutes to hours) are not conducive to such studies because of possible follow-up reactions. When a sample is electrolyzed at a constant potential, the i-t response, limited by the rate of mass transfer of a redox species to the electrode surface, can be modeled by the following equation (assuming that the concentration of electroactive species remains uniform over the solution volume) [1].