Coupling a Wireless Bipolar Ultramicroelectrode with Nano-electrospray Ionization Mass Spectrometry: Insights into the Ultrafast Initial Step of Electrochemical Reactions

摘要

We report a new mass spectrometric method for detecting electrogenerated intermediates. This approach is based on simultaneous activation of electrospray ionization and redox reaction on a wireless bipolar ultramicroelectrode, which is fabricated in the tip of a quartz nanopipette. The hollow structure of the ultramicroelectrode permits rapid transferring the transient species from electrode-electrolyte interfaces into the gas phase for mass spectrometric identification on the time scale of microseconds. The long-sought fleeting intermediates including TPrA(.+), whose lifetime in solution is only 200 mu s, and catecholamineo-semiquinone radicals, the second-order rate constant of which is typically 10(9) m(-1) s(-1), were successfully identified, helping clarify the previously hidden reaction pathways. Accordingly, our method may have wide applicability in exploring the dynamics of many electrochemical reactions, especially their ultrafast initial steps.