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Filter Integrity Testing

Hall Pyke is an Irish supplier of Filter Integrity Testing. Filter Integrity Testing is a fundamental requirement of critical process filtration applications in the pharmaceutical industry and more. Hall Pyke can carry out Filter Integrity Testing either at our clients’ onsite location or in our own labs at Hall Pyke. We can carry out tests on a myriad of filters including PALLTM, Parker Dominick Hunter™, Amazon™, Millipore™ and Sartourious ™.

Determining if a sterilizing grade filter is integral can be done via non-destructive integrity testing.

The test parameters for sterilizing grade membrane filters are based on correlating the test parameters with the LRV of the filter against a 107 CFU/cm2 challenge with Brevundimonas diminuta.

The filter cartridges can be tested by industry standard procedures as recommended in PDA Technical Report 26.
The test parameters are dependent on the surface tension of the wetting fluid to be used. Therefore, the parameters used in the procedures, listed below, assume the wetting fluid to be water. For test values using wetting fluids other than water the adjusted parameters have to be determined. Hall Pyke can carry out and advise on the following filter integrity test procedures:

  • Bubble Point
  • Water intrusion test
  • Forward Flow Diffusion

Bubble point test

The basis for the integrity testing of filters depends upon the interpretation of airflows through membranes wetted by water or other fluids. A bubble point test is designed to determine the pressure at which a continuous stream of bubbles is initially seen downstream of a wetted filter under gas pressure. The bubble point measurement identifies the largest (diameter) pores present in a membrane by the differential pressure required to empty them of their water. The largest (diameter) pores are vacated first. The pores thus sized are correlated with their ability to restrain the passage of organisms. It is this correlation that enables a filter to be characterized and selected for an application requiring a given pore retention value.

The differential pressure supplies the work function necessary to disrupt the bonding between the water molecules and the molecules of the hydrophilic pore surface that constitutes wetting, and to forcibly separate the water from the pore walls. The bonding strength of the wetting interaction to be overcome is peculiar to each filter/fluid combination.

The utility of the bubble point derives from its identifying a filter’s largest pores as measured by the differential pressure required to expel the water from a wetted filter.


Reverse Bubble Point Test


Diffusion flow test

In the diffusive flow test the membrane is wet with water, and the upstream gas is then held constant at a specified pressure near, but somewhat below, the bubble point of an integral filter. A measurement is made of the flow rate of gas through the filter and compared to the manufacturer’s specification.

A measured flow rate equal to or less than the specified value indicates that the filter Is integral. A higher flow rate indicates that the filter being tested has pores or defects which were purged of water at the test pressure, resulting in bulk flow through the filter.


Water Intrusion Test (WIT)

The water intrusion test measures the decay rate of a pressure level imposed upon a hydrophobic filter enveloped by water. Using an automated integrity tester, a particular decay level is identified as the point at which water enters the largest pores of the filter. The water intrusion test is widely used in the pharmaceutical industry. At Hall Pyke we can carry out water intrusion testing for you and your business.


Hydrophilic Surface Deposits

The water intrusion test depends upon and measures the hydrophobicity of the filter. Only the experimentally demonstrated correlation of its values with the entrance of water into the hydrophobic pore structure establishes it as a filter integrity test. But the basic measurement of filter hydrophobicity is itself an inherent requirement in its pertinence to air filter reuse. Consider an integral air filter that contains hydrophilic deposits upon its surface. They may encourage microbial growth and ultimately, organism penetration. Solely ensuring air filter integrity, however essential, is not enough in air filter usage. The filter’s full hydrophobicity must also be assessed to ensure freedom from compromising hydrophilic impurities.