Rapid and precise monitoring of electrochemical intermediates using a portable three-electrode electrospray sheet EC-MS system

A portable three-electrode spray sheet EC-MS system for in-situ reaction monitoring • Decouples spray high voltage from precise electrochemical control via floating ground • Seamlessly couples with HRMS to resolve complex electrochemical reaction networks • Integration with miniMS enables operando monitoring of synthesis in fume hoods • Offers guidance for the complex multi-parameter optimization of green EC engineering Electrochemistry (EC) is a core technology for elucidating charge transfer mechanisms and enabling catalytic innovation and material synthesis. However, characterizing reaction intermediates during EC process remains challenging owing to their high diversity, short lifetimes, and low concentrations. Recently, mass spectrometry (MS) has become a key tool for such studies due to its precise qualitative and quantitative capabilities. Although various in-situ MS techniques based on electrospray ionization (ESI) have been developed to detect short-lived intermediates, existing in-situ EC-MS devices are usually hindered by the voltage incompatibility between EC control and ESI high voltage, along with complex designs and cumbersome operations. Herein, we developed a portable EC-MS system featuring a three-electrode spray sheet. This sheet is fabricated by screen-printing electrodes onto a polyethylene terephthalate substrate with a sharp 90° tip, which is hydrophilically modified with 0.01% gelatin to function as both an electrochemical reactor and a spray emitter. Driven by a homemade floating-potential controller, the system enables precise three-electrode electrochemical control and direct ionization monitoring of intermediates. Characterization via scanning electron microscopy and dopamine experiments confirmed its stability and precise controllability, while DMA oxidation tests demonstrated its capability for analysis of microsecond level intermediates. The modular design allowed coupling with a high-resolution mass spectrometer to elucidate the oxidation pathway of sulfadiazine, clarifying the relevant metabolic pathways. Furthermore, integration with a miniature mass spectrometer enabled rapid on-site monitoring of sulfadiazine-catechol synthesis in a fume hood, demonstrating its convenience and scalability. This work provides a rapid and precise tool for monitoring liquid-phase electrochemical reactions. Download: Download high-res image (146KB) Download: Download full-size image