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).

Glasartige Kohleelektroden weisen nach ihrer Behandlung mit O2‐RF‐Plasma an ihrer Oberfläche chinonartige Strukturen auf, die mit Methoden der phasenempfindlichen Wechselstrom‐Voltammetrie und durch Reaktion mit o‐Phenylendiamin als I,2‐Naphthochinon und 9,10‐Phenanthrenchinon identifiziert werden.

This review deals with the literature (covered up to August 1983), the characterization and the applications of Surface‐Modified Electrodes (SME). As a special class of SME's, the Enzyme‐Modified Electrode (EME) is introduced. Three types of modification procedures are distinguished; i.e. covalent modification, adsorption modification and polymer‐film modification. A further subdivision is made for catalysts attached to the electrode surface directly or via a bridge molecule. The characterization of SME's is mainly achieved via electrochemical techniques such as cyclic‐ and ac‐voltammetry. This theory is briefly described and illustrated with some of our own results. The name EME is used for a system in which the enzyme is immobilized at the electrode surface, such that direct electron transfer between electrode and enzyme becomes possible. The last part of this review deals with the applications of SME's and EME's. Examples are given of some already realized and of some possible applications.

A quasi‐reversible electrochemical behaviour of horse‐heart cytochrome‐c is obtained at gold and platinum electrodes in the presence of 4, 4′‐bipyridine. Transparent tin‐dioxide and glassy‐carbon electrodes, modified with pyridine groups, also give rise to a quasi‐reversible response of cytochrome‐c. From impedance measurements and from cyclic‐ and ac‐voltammetry at the gold an platinum electrodes, reaction rate constants (k0′) of 0.6·10−4 to 1.4·10−4 m·s−1 were determined for cytochrome‐c in the presence of 4, 4′‐bipyridine. In both cyclic‐ and ac‐voltammograms, an adsorption peak is observed at −0.2 V vs. SCE. This peak is ascribed to strong adsorption of both ferri‐ and ferrocytochrome‐c. The 4, 4′‐bipyridine molecule creates a suitable interface at the electrode surface. Although no interaction between 4, 4′‐bipyridine and cytochrome‐c could be detected in solution, a specific interaction is believed to be present between adsorbed 4, 4′‐bipyridine and cytochrome‐c.

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