Generator/Collector Experiments with a Single Electrode: Introduction and Application to Exploring the Oxidation Mechanism of Serotonin

The facile chemical modification of a graphite electrode with pH sensitive redox active molecules results in the formation of a generator/collector electrode system using a single electrode. Using the oxidation of serotonin as a model system, we demonstrate that the single generator/collector electrode is capable of measuring changes in local pH immediately adjacent to the electrode surface, i.e., within the diffusion layer during the oxidation process. Comparison of experimental data with numerical simulations was used to ascertain that the serotonin oxidation mechanism in poorly buffered media initially involves the transfer of two electrons and only one proton in an electrochemical, chemical, electrochemical (ECE) mechanism. This approach compares favorably in terms of sensitivity to traditional double-electrode experiments such as the use of rotating ring-disk electrodes.