The integrity of the sterilised filter should be tested and recorded immediately after use by anappropriate method. The common methods include Bubble Point test, Diffusion Flow test or Pressure Hold test.
When the filter membrane is wetted bt a proper liquid; the liquid will be held in the pore of the filter by surface tension and capilary forces. The minimum pressure required to force liquid out of the biggest pores is a bubble point pressur. The formula is as followed;
At the 80% pressure of the minimum bubble point, the gas flow rate is measured diffusing through the liquid-filled pores of a wetted membrane to downstream.
Under a low differential pressure, the amaller flow is squeezed into the filter membrane to form a certain flow rate despite of the preventing force caused by a hydrophobic membrane.
