Disclosed is a piezoelectric
resonator, a process for the fabrication thereof and its use as a sensor element, which implemented in a through-
flow cell, is integratable in a measurement
system for the determination of the concentration of a substance contained in a liquid and / or for the determination of the physical properties of the liquid. The piezoelectric
resonator is designed plane and is provided on its surface with
electric contact areas for an
electrode and a counter
electrode, which is connectable to a
signal source as well as to a
measurement device. For measuring, the piezoelectric
resonator is brought into contact with the to-be-examined liquid on one side, with the resonator responding to the accumulation of the
mass of the to-be-detected substance or to a change in the physical properties of the liquid by changing its
resonance frequency and / or
oscillation amplitude.The present invention is distinguished by the fact that the piezoelectric resonator is provided with
contact electrode areas which is contactable from one single side of the resonator. The resonator is the heart piece of a sensor element, which is integrated in a through-
flow cell. The through-
flow cell us insertable module-like in a measurement arrangement for determining the concentration of a substance contained in a liquid and / or determining the physical properties of the liquid.