Characterization and Application of a Mercury Hemisphere Microjet Electrode

Abstract

The microjet electrode (MJE) is a hydrodynamic electrode in which a fine jet of solution impinges from a nozzle on an ultramicroelectrode (UME) under conditions of variable and high mass transfer rates. An assessment is made as to whether this methodologyhitherto employed with solid disk electrodes alonecan be used in conjunction with hemispherical mercury electrodes grown on Pt UMEs. Mass transfer imaging experiments, in which the transport-limited current at the Hg UME is monitored as a function of nozzle position, demonstrate that local mass transfer rates from the impinging jet are similar to those measured earlier at disk electrodes. When the electrode and nozzle are configured to produce the maximum mass transfer rates, the transport-limited current−flow rate characteristics, at low to intermediate flow velocities, are shown to be well-defined and predictable, by analogy to the rotating hemisphere electrode. At higher flow rates, the electrode becomes physically unstable and eventually detaches from the Pt UME. Within the physically stable region, mass transfer coefficients up to 0.2 cm s-1 are readily attainable, making the device attractive for both electroanalysis and kinetic applications. In particular, the use of the Hg hemisphere MJE for stripping analysis is shown to greatly increase the efficiency of the preconcentration step, compared to Hg UMEs in stationary solution or alternative flow configurations.