Study of the effect of ultrasound on mass transport to a microelectrode

Microelectrodes (Pt, Au 25 μm, 10 μm diameter and C 6 μm diameter) have been employed to record individual cavitation events produced as a consequence of high intensity ultrasonic irradiation of a solution containing a redox probe. Cavitation events are detected at a microelectrode as a series of current-time transients. The potential dependence of the observed events in relation to the redox chemistry of the particular probe under investigation is demonstrated. Ferrocene and hexaamine ruthenium(III) chloride have been employed as model redox systems. The effects of temperature, solvent, electrode/ultrasonic source separation, position of the electrode with respect to the ultrasonic source and ultrasonic intensity on the frequency and magnitude of the observed cavitation events are demonstrated. The shapes of the current-time transients recorded are analyzed with comparison to conventional chronoamperometry at microelectrodes. Mass transport coefficients of up to 1.6 cm s-1 are reported.