The bubble point test is a non-destructive test used to determine the maximum pore size of a hydrophilic filter membrane. It is based on the fundamental principles of capillary action and the pressure required to displace a wetting liquid from the pores of a filter. Procedure overview: 1. The filter membrane is thoroughly wetted with a suitable liquid (e.g. water) to ensure that all the pores are filled via capillary action. 2. Gas pressure is then applied incrementally to the upstream side of the wetted filter. 3. The downstream side of the filter assembly is immersed in a water bath to enable the emission of gas to be observed visually.

4. Initially, at low pressures, gas diffuses through the water-filled pores via dissolution and diffusion, generating a sparse, intermittent stream of bubbles downstream. 5. The pressure is then gradually increased until it exceeds the capillary retention force of the liquid in the largest pore. At this critical pressure, the liquid is forcibly expelled from the pore, enabling convective gas flow in larger quantities. 6. The onset of a continuous, steady stream of bubbles from the largest pore is then visually detected. The gas pressure recorded at this transition point is defined as the bubble...