Pharmaceutical Filtration

Integrity Testing of Sterilising–Grade Filters

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Therefore, this means that the use of such a small air filter enables bidirectional protection in the tubing. However, it must be ensured that this filter in the test line will not adversely affect the test results. Virtually identical integrity test results are yielded both when a small vent filter of the type Midisart 2,000 (0.2 μm PTFE, filter area 20 cm²) is used and when such a protective filter is not installed.

Ultimately, the air filter must be sized so that air flow during the integrity test phase is not impeded. A sterilising-grade filter of the type Sartopore 2 (10’’, 0.2 μm), for instance, has a diffusion limit of 18 mL/min at a test pressure of 2,500 mbar. At a differential pressure of 100 mbar, the Midisart filter permits a flow rate of approximately 8 L/min and, accordingly, does not limit the air flow.

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Protective Filters Bring New Challenges

The use of such a protective filter is unproblematic even for carrying out a bubble point test. Although the air flow rate overproportionately increases once the bubble point is attained, the rate still remains well below the critical limit. This can be proven if the same sterilising-grade filter is tested with and without a protective filter in the test line (Fig.1).

The curves with and without a protective filter are nearly congruent, and the integrity test unit measures the same bubble point. This shows that the Midisart filter in the test line doesn’t have any limiting effect, yet simultaneously protects the test unit.

Use of External Vent Valves

For specific applications, it is advisable to use external vent valves. During venting, which is necessary once the test phase has ended, the internal vent valve in the test unit will remain closed and only the external valve will open directly on the housing. As a result, this ensures that the overpressure in the housing can be released only via the external valve and any liquids or aerosols carried along in the air stream cannot flow back into the test unit.

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