Because the integrity test is non-destructive, it can be done both before and after filtration without causing damage to the filter. At the same time, they confirm that the filter is in good working order and that it performs as expected in terms of performance and retention. During validation, microorganisms are removed from the final filter using the same membrane that was employed during product development.
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Relevant integrity tests, such as the following, can certify that the filter is complete and ready for continuing service:
- It verifies that the filter is of the proper quality, has been properly placed, and is not damaged.
- The air filter housing can be tested for integrity by closing the upstream and downstream valves to ensure that all housing O-rings are in good working order.
- It verifies that the filter complies with the manufacturer's requirements.
- It is necessary for process verification, monitoring, and batch documentation, as well as during the assessment of process documentation.
- Finally, it makes it easier to pinpoint the source of contamination.
If the integrity test is passed but there is contamination downstream of the filter, the following underlying cause is most likely:
- Port for contamination sampling
- Contaminated seal
- Contaminated filling head
- Bottle that has been contaminated
Before being released, Alfa Chemistry filters are all integrity checked during the manufacturing process. To verify the results, there will be manufacturing site-specific integrity test techniques and production integrity test limits.
Recommended Integrity Test
Forward flow and pressure decay are two integrity tests Alfa Chemistry recommends for microbial reduction and sterilizing grade membrane filters. The bacterial challenge test result is linked to the forward flow value. The forward flow value and the upstream volume of the housing are used to determine the pressure decay value.
The microbial elimination or reduction level specified during the initial filter verification is the subject of these tests. They can be used as a non-destructive test after disinfection and at the conclusion of a production batch to demonstrate that the filter assembly is complete.
Forward Flow Test
- The pressure in the filter housing's upstream volume is kept constant at the filter's specified forward flow test pressure.
- The total air flow is monitored by upstream or downstream test equipment via the filter and is made up of a diffuse flow through the wet holes and an overall flow through the apertures or faults.
Pressure Decay Test
- The pressure in the filter housing's upstream volume is maintained at the filter and housing's particular pressure decay test pressure.
- The upstream test equipment measures the total airflow through the filter.
- The drop in pressure is measured by pressure decay.
Water for Intrusion Test (WIT)
- The microbial retention is associated with the water flow measured through the hydrophobic filter.
The most sensitive integrity test for bactericidal capacity and microbial reduction is the bacterial retention test; however, because this test is destructive, the filter cannot be utilized after the test because it will be contaminated by the test bacteria. Non-destructive integrity testing, if applicable, is a good indication of bacterial challenge retention.
Practical Considerations When Performing Integrity Testing
NO.1 Choice of Integrity Test Liquid
- Standard "reference" test fluid
- Water: Hydrophilic and hydrophobic filters
- FF/PH/BP hydrophilic filter
- WIT hydrophobic filter
- Alcohol/Water: Hydrophobic filter
- 60/40 IPA/water is common
- 25% tert-Butanol (Pallsol)
- 100% alcohol (IPA, ethanol) is not recommended (high diffusion)
NO.2 Selection of Pressurized Gas
- Acceptable test gas: air, nitrogen, argon
- Unacceptable test gas: carbon dioxide (solubility problem), oxygen (reactivity problem)
NO.3 Temperature
During the integrity test, the temperature should not rise more than 5°C. The gas diffusion in the fluid will alter if the temperature varies significantly. For integrity testing, a temperature range of 20 °C to 5 °C (68 °F to 9 °F) is recommended. Temperature variations have a significant impact on gas pressure. A 0.3 percent volume change occurs when the temperature changes by 1 degree Celsius.
NO.4 Upstream
When it comes to pressure decay testing, upstream volume is crucial. The structural integrity of filters in applications where they are successfully regenerated will determine their service life.