The adsorbance of each of these molecules resulted in changes in both frequency and resistance. The bound analyte mass is proportional to changes in the oscillation frequency of the quartz crystal as described by the Sauerbrey equation (Eq. 1), where Δf is the change in frequency, C f is the known sensitivity factor of a 5-MHz crystal (56.6 Hz cm 2 μg −1 ), and Δm is the change in mass [41] :