Mapping Reaction Pathways by <i>In Situ</i> Step Sweep Voltammetry Flow Electrochemical Mass Spectrometry

A step sweep voltammetry (SSV) flow electrochemical (EC) mass spectrometry (MS) platform was developed for real-time and <i>in situ</i> mapping of EC reaction pathways. By integrating a flow EC cell into the pneumatic spray nozzle followed by atmospheric chemical ionization, this setup was capable of <i>in situ</i> MS monitoring of short-lived EC intermediates with enhanced sensitivity. This setup also realized precise measurement and control of the electrode potential during <i>in situ</i> EC-MS analysis, which can provide detailed information on the interplay of reaction pathways under different electrode potentials. Taking the EC reductive cross coupling of nitroarenes with arylboronic acids as an example, SSV-MS had identified 13 compounds among four reaction pathways. Among these, the electrode potential of active nitrene and cross coupling intermediates were measured for the first time and the structure of the nitroso coupling complex was also confirmed by MS. With the systematic measurement of electrode potential of the intermediates and products, SSV-MS had clearly mapped out the synergies and competitions between different reaction pathways, offering key insights for optimizing reaction conditions and investigating reaction mechanisms for EC research.