QCM apparatus

A quartz crystal microbalance, QCM, sensor apparatus comprising:

• a sensor holder having a compartment for receiving a QCM sensor, said compartment having a substantially planar extension;
• a first temperature sensor and a second temperature sensor arranged separated from each other along a line transverse to said planar extension;
• a controller configured to determine a temperature difference between the two sensors, and to operate the QCM sensor apparatus based on this temperature difference;
• a plurality of sample fluid containers;
• a fluid selector unit for selectively placing one of said sample fluid containers in fluid connection with a measurement cell formed above the QCM sensor, said fluid selector unit having:
• a plurality of inlet ports, each inlet port in fluid connection with a sample fluid container,
• a sensing outlet configured to be in fluid connection with said QCM sensor, and
• a valve arrangement for selectively connecting one of said inlets to said outlet.