Differential electrochemical mass spectrometry (DEMS) enables real‐time detection of volatile products formed at an electrode. However, its application in organic solvents is hindered by their volatility and by solvent‐induced swelling or permeation of the membrane that defines the liquid/vacuum interface, compromising stable product transfer to the mass spectrometer. Here, we report the experimental demonstration of quantitative DEMS measurements in acetonitrile, enabled by a rational optimization of the membrane interface together with the operating conditions in a dual thin‐layer flow cell. Starting from the hydrogen evolution reaction (HER) on polycrystalline platinum (Pt) in 0.5 M HClO 4 aqueous electrolyte as a model system, we systematically examined how flow rate, membrane properties, that is porosity and thickness, and the inclusion of a cold trap influence gas transport efficiency in the DEMS cell. Acetonitrile, one of the most widely used solvents in molecular electrocatalysis and organic synthesis, was selected as a particularly demanding test case due to its high volatility and swelling of PTFE membranes. The methodology was evaluated for both HER and oxygen evolution reaction, and a linear and quantitative relationship between faradaic current and detected gas flux was obtained on the timescale of electrochemical measurements. The systematic variation of key DEMS parameters in aqueous media provided the basis to rationally select conditions most likely to enable reliable analyte detection in this demanding solvent. Overall, this work provides practical design guidance for the controlled operation of DEMS and establishes a robust methodology for extending DEMS to nonaqueous environments relevant to organic synthesis.
Salamé et al. (Sun,) studied this question.