Noncontact Extraction Mass Spectrometry with Bubble Extraction Ionization Facilitates Operando Monitoring Electrochemical Reactions

An in-depth study of electrochemistry (EC) requires a sensitive and real-time monitoring platform. Herein, we report a bubble extraction ionization electrochemical mass spectrometry (BEI-EC-MS) platform for monitoring the reaction products and transient intermediates in the EC reactions. Compared with previous online EC-MS methods, BEI-EC-MS employs in situ soft ionization within the electrolytic cell, eliminating the need for additional voltages during the reaction monitoring process. The ascending bubbles effectively extract and concentrate compounds from both the surface of the EC electrode and electrolyte, enabling long-term monitoring in both positive and negative MS modes. Monitoring experiments of aniline (ANI) EC polymerization verified the platform performance and successfully captured short-lived radical intermediates. The platform was then used to monitor the long-term EC degradation of the pollutants dinotefuran (DNT), rhodamine B (RhB), and perfluorooctanoic acid (PFOA). A series of intermediates and products were characterized by using BEI-EC-MS, including various radical ions measured for the first time, providing pivotal evidence for the degradation mechanisms of these reactions. We anticipate that our approach will not only provide new protocols for monitoring EC reactions and assist in conducting mechanistic studies but also be readily adaptable in conventional electrochemical laboratories with the mere addition of a bubble generation device.