3 – Which is the best outer and inner diameter of tubing ?

You should use tubing whose outer diameter is OD = 3.2 mm and internal diameter is ID = 1.6 mm.

If you are using openQCM with a peristaltic pump we suggest to use a smaller tube for the one in the peristaltic pump, for example Tygon tubung ID = 0.51 mm. Actually you can reduce the frequency fluctuations by reducing the tube diameter in the peristaltic pump.