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The theory of "two-dimensional voltammetry" using arrays of gold channel microband electrodes ranging in size from the millimeter to the micrometer scale is extended to permit the deduction of electrochemical rate constants through the analysis of hydrodynamic voltammograms as a function of both electrode size and electrolyte flow rate (convection). The technique is applied to the reduction of p-chloranil and the oxidation of 2,3,7,8-tetramethoxythianthrene both in acetonitrile solution and electrochemical rate constants are reported.

Voltammetric experiments under intense microwave field conditions have been carried out at a carbon microfiber electrode, an array of carbon microfiber electrodes, and at a boron-doped diamond electrode. For the reversible one electron redox systems Fe(CN)63-/4- and Ru(NH3)63+/2+ in aqueous KCl solution increased currents (up to 16 fold at a 33 μm diameter carbon microelectrode) and superheating (up to ca. 400 K at all types of electrodes) are observed. Electrodes with smaller diameter allow better signal enhancements to be achieved. From the missing effect of the supporting electrolyte concentration on the microwave enhanced currents, it can be concluded that effects observed at carbon electrodes (microwave absorbers) are due to the interaction of microwaves with the electrode material whereas for metal electrodes (microwave conductors) effects are dominated by the interaction of the microwaves with the aqueous dielectric. Short heat pulses can be applied by pulsing the microwave field and relatively fast temperature transients are observed for small electrodes. For the irreversible two electron oxidation of L-dopa in aqueous phosphate buffer, different types of effects are observed at glassy carbon and at boron-doped diamond. Arrays of carbon microfibers give the most reproducible and analytically useful current signal enhancements in the presence of microwaves. © 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.

Microwave activation of electrochemical processes has recently been introduced as a novel technique for the enhancement and control of processes at the electrode-solution interface and is employed here to improve the analytical detection of Pb2+. Instead of the conventional mercury-based accumulation and stripping procedure, mercury-free boron-doped diamond electrodes are employed. The deposition and anodic stripping detection by square-wave voltammetry of Pb2+ in a 0.1 M HNO3 solution is shown to be strongly enhanced by microwave activation at boron-doped diamond electrode. The temperature at the electrode-solution interface is calibrated with reversible redox couple Fe3+/Fe2+ (4 mM Fe3+, 4 mM Fe2+) in 0.1 M HNO3 and a standard addition procedure is developed for the sensitive detection of Pb2+ concentrations from 1 μM to 5 μM. The limit of detection by square-wave voltammetry after 20 s deposition time was found to be 0.1 μM and 1.0 μM with microwave activation and without microwave activation, respectively. Then, the Pb content in a water sediment sample detected by anodic stripping voltammetry at boron-doped diamond electrodes is shown to be in good agreement with two other independent analytical procedures based on ICP mass spectroscopy and on sono-cathodic stripping voltammetry.

A novel electrochemical cell based on a flow through system in a microwave cavity is shown to allow voltammetric experiments under microwave conditions. Focusing of the microwave radiation at the electrode-solution (electrolyte) interface creates conditions of extreme localized heating with an inverted thermal gradient within the diffusion layer of the electrode and convective flow. The deposition and anodic stripping detection by square-wave voltammetry of Cd2+ in a 0.1 M acetate buffer solution is shown to be strongly enhanced by microwave activation. The temperature at the electrode-solution interface is calibrated with the reversible redox couple Ru(NH3)63+/2+ in 0.1 M acetate buffer. The effect of microwave activation on the square-wave voltammetric responses for the reduction of Ru(NH3)63+ and for the detection of Cd2+ in 0.1 M acetate buffer solution are studied. In the presence of a nonionic surfactant, Triton X-100, which blocks the electrochemical Cd2+ response under conventional conditions, microwave activation is shown to have a considerable effect in enhancing the sensitivity for Cd2+ detection.