Simple QCM-D measuring circuit for aqueous applications

Quartz crystal microbalance with dissipation (QCM-D) measuring system was designed and constructed. It composes of oscillator with tri-state buffer and microcontroller ( dsPIC 33FJ128GP708). Laboratory made 12 MHz QCM with gold electrode was used as a part of oscillator. Dissipation factor of the QCM was determined from time constant of the oscillation signal decreasing after the oscillator was turned-off. Detection limit of the system was evaluated from the measurement of de-ionized water (DI water) dropping on the QCM surface. It was found that the system could detect the DI water down to less than 0.5 ul. The system was also applied to detect the alcohol content in DI water. The detection limit of 1% alcohol was observed.