A high‐stability quartz crystal microbalance electrode for simultaneous solution‐phase electrochemistry/microgravitometry

A quartz crystal microbalance (QCM) oscillator circuit is described which incorporates a high‐gain feedback amplifier controlled by an automatic gain network. Signal level in the oscillator feedback loop is automatically optimized to provide sufficient gain necessary to sustain stable oscillation, but not so much gain as to induce waveform clipping, which would detriment frequency stability. The crystal is driven and loaded by a low‐impedance network, and one side of the crystal is held at low impedance to ground. In this way, the microbalance crystal may be used in place of a working electrode in an electrochemical apparatus. Gravitometric studies at the surface of the electrode may be combined simultaneously with cyclic voltammetry, chronocoulometry, chronoamperometry, or any other electrochemical experiment in aqueous and nonaqueous solutions. The QCM signal is heterodyned with a reference signal to produce a difference frequency on the order of a few hundred Hertz. An optional frequency‐to‐voltage converter is also described so that the beat frequency can be monitored in real time on a chart recorder. The results of a simultaneous electrochemical/microgravitometry experiment involving the growth and redox cycling of a Prussian blue film on the surface of the QCM are presented.