An apparatus for measuring electrochemical and viscoelastic properties of a liquid includes two sensing components, an electrochemical impediance spectroscopy component and a quartz crystal microbalance component positioned within a housing for receiving a liquid for monitoring and arranged so that each component shares a common electrode. Means are provided to simultaneously apply a sinusoidal waveform across the electrodes whereby information on the electrochemical and viscoelastic properties of a liquid being monitored is obtained.