A Combined Flow Cell and Cold Trap Geometry of Online Differential Electrochemical Mass Spectrometry for Enhanced Detection Sensitivity

Online differential electrochemical mass spectrometry (DEMS) enables real-time detection of volatile reactants, intermediates, and products, providing temporally and chemically resolved signals that facilitate the understanding of electrochemical reaction kinetics. In this work, we incorporated a cold trap accessory into the membrane-inlet DEMS open flow cell design, achieving highly sensitive detection of mass ion signals over a Faradaic current range from 50 μA to 100 mA and enabling product selectivity quantification in H₂ evolution and CO₂ reduction reactions with subsecond temporal resolution. Numerical simulations reveal that pervaporated H₂O solvent dominates the flux of species across the polytetrafluoroethylene (PTFE) membrane into the vacuum system, whereas the analyte concentration can be improved by 2 orders of magnitude after condensing these H₂O molecules for subsequent ionization. Using monolayer CO stripping on a polycrystalline Pt electrode as a case study, the mass ion cyclic voltammograms for CO₂ successfully replicate that of Faradaic current voltammograms corresponding to ca. 4.37 nmol of CO oxidation, demonstrating a 290-fold improvement in CO₂ detection sensitivity with the cold trap design. This system's sensitivity and capability for real-time monitoring of volatile species demonstrate its utility in elucidating reaction kinetics and complex pathways across a broader range of gas-involved electrochemical processes.