Differential electrochemical mass spectrometry (DEMS) can be used not only to identify products or intermediates of continuous faradaic reactions, but also to characterize submonolayer amounts of adsorbates on polycrystalline and single crystal electrode surfaces by means of their desorption, because of its high sensitivity. One possibility to achieve this is to oxidize a carbonaceous species to CO 2 , which is quantitatively detected in the mass spectrometer. Many adsorbates can also be desorbed at certain potentials as such, or as the hydrogenated product, allowing a more direct characterization of the adsorbate. In some cases, a nonreactive desorption can be induced by displacement with a second adsorbate, yielding additional information. Interfacing an electrochemical cell to a mass spectrometer via a porous Teflon membrane can be achieved with a variety of cells. These will be described together with their specific advantages and characteristics. (J Am Soc Mass Spectrom 2004, 15, 1693-1706

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The combination of differential electrochemical mass spectrometry (DEMS) and electrochemical quartz crystal microbalance (EQCM) is possible by means of a new dual thin layer cell. Thus, simultaneous real‐time measurements of volatile products and deposited (or dissolved) species can be performed, which is demonstrated for CO‐adsorption and desorption processes on Pt and a Pt‐Ru alloy in sulfuric acid. In particular, it is shown that on a Pt‐Ru alloy, electrode anions are adsorbed even at 0 mV vs. reversible hydrogen electrode. © 1999 The Electrochemical Society. All rights reserved.

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