Successful Wetting For Filter Integrity Testing In Volume-Restricted Systems

By Brian Bory, Barbara Frei, Rolf Jaenchen and Jörg Schubert

Filters with a qualified retention for bacteria, mycoplasma or viruses are commonly used in many pharmaceutical processes. In a validated GMP process, these filters must be routinely tested for integrity. For both of the most commonly used filter integrity (IT) tests, the Forward Flow Test and the Bubble Point Test, the filter membrane must be completely wetted with an appropriate wetting liquid before starting of the test.

The automated test instruments that are used for filter integrity testing have been improved during the over 40 years that filter integrity testing has been performed. The Palltronic Flowstar IV instruments and Palltronic AquaWIT IV systems represent the latest generation of best-in-class integrity test equipment. The instruments have a very sensitive measurement system and are capable of detecting almost all conditions, where external influences could jeopardize the validity of the test result. Apart from temperature fluctuations, filter wetting has become the main factor to cause false failures during the filter integrity test.