We present the construction and some first applications of an On-line electrochemical mass spectrometry system for detecting volatile products formed during electrochemical reactions at a single-crystal electrode in hanging meniscus configuration. The system is based on a small inlet tip made of porous Teflon and a Peek holder, which is brought in close proximity (ca. 10-20 lm) to the electrode surface. The tip is connected to the mass spectrometer by glass and metal tubing. Because of the small amount of gas entering the mass spectrometer, no differential pumping is needed during the measurement. The tip construction and preparation introduced here leads to reproducible voltammetry with very good cleanliness characteristics. The presence of the tip has no significant influence on the blank voltammetry of a Pt(111) in sulfuric acid, and on voltammetric responses for CO adlayer oxidation, methanol oxidation, and hydroxylamine electrochemistry on Pt(111). The formation of gaseous products in these reactions can be followed accurately and is in good agreement with earlier results obtained by other mass spectrometric or spectroscopic techniques. The time response and tailing of the setup is on the order of seconds and mainly determined by the distance between the tip and the electrode.

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The irreversible adsorption of several C3 alcohols, 1-butanol, and ethene on platinized platinum has been studied with Fourier transform IR spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS) in perchloric acid electrolyte. Apart from 2-propanol, all studied alcohols display C-C(O) dissociative adsorption as the only pathway active in the formation of irreversible adsorbates. 1,2,3-Propanetriol is the only compound that is fully converted to adsorbed CO, while all other primary alcohols generate hydrocarbon adspecies in addition to CO. No further C-C bond breaking is observed in these hydrocarbon adspecies, which were found to be highly dehydrogenated. The hydrocarbon species can be fractionally hydrogenated off the surface to form corresponding gaseous compounds. 2-Propanol and ethene do not undergo C-C dissociation to form CO but are dehydrogenated considerably. For 2-propanol and ethene it was found that a small amount of oxygen incorporation occurs on the C 1 position, followed by decarbonylation to form CO.

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The composition of oxidic groups at a glassy‐carbon surface has been studied using phase‐sensitive ac‐voltammetry. Two types of quinones have been identified, i.e. the 1, 2‐naphtoquinone‐ and the 9, 10‐phenanthrenequinone‐like structures. The 1, 4‐naphtoquinone‐ and 9, 10‐anthraquinone‐like structures are, most probably, also present at the glassy‐carbon surface, although in lower surface concentrations. The o‐quinones can be converted into the corresponding benzophenazines (by reaction with o‐phenylenediamine), which are also electroactive. The differences in redox potentials between the quinones and phenazines make detection of intermediate reaction stages possible. The effect of oxygen and argon rf‐plasma treatment upon the composition of the quinone‐surface groups has also been studied. Pretreatment of the glassy‐carbon surface by an oxygen rf‐plasma is a very powerful and clean oxidation technique. Argon rf‐plasma increases the 9, 10‐phenanthrenequinone‐like structures, while oxygen rf‐plasma, with successive cooling in an argon atmosphere, diminishes the surface concentration of quinone structures and increases that of the acidic surface groups, as can be concluded from modification experiments. From phase‐sensitive ac‐voltammetry measurements, a lower limit of 103 s−1 was determined for both the quinone and the phenazine surface reaction rate constants (ks).