Discover the essential filter integrity testing devices for maintaining the suitability and integrity of membrane filters in the industry.
Integrity tests are non-destructive tests and, as such, can be performed before filtration and after filtration without affecting the filter itself. At the same time, they provide confidence that the filter is intact and delivering the expected performance and retention characteristics.
Filter integrity testing during validation relates to the microbial removal of final filters based on membranes used during product development. For this purpose:
- Filters are tested with various integrity values under specific conditions and challenged with microbes.
- The results of the microbial challenge test are plotted against the integrity test values for comparison.
- Based on the desired microbial removal level - sterilizing grade or a specific log reduction value (LRV) - an acceptable test limit for the integrity test is established. (e.g., mL/min or mbar pressure drop)
Integrity Test Values and Microbial Challenge
A correlated integrity test can confirm filters are integral and suitable for continued service and will provide the following benefits:
- Ensures the filters are in the correct grade, installed correctly and free from damage.
- Integrity tests can be performed on an empty filter housing with closed upstream and downstream valves to verify that all o-ring seals are intact.
- It confirms that the filter meets the manufacturer's specifications.
- It is essential for process validation, monitoring and batch record files and could be helpful during process documentation review.
- Finally, it allows for faster identification of contamination.
- If the filter passes the integrity test and contamination is present downstream of the filter, then the following root causes are most likely:
- Contaminated sampling port
- Contaminated filling heads
- Contaminated closures
- Contaminated bottles
Filter Integrity Test Solutions from Pall providing you with confidence
100% of Pall filters are integrity tested during manufacturing before release. A production integrity test limit is specific to the manufacturing site's integrity test method and the validation results. Additionally, there is a customer integrity test limit suitable to use with Palltronic® integrity test devices supplied by Pall for customer use (e.g., Palltronic Compact Touch Integrity Test Device).
The Pall Compact Touch (Integrity Test Device)
Recommended Integrity Tests to confirm the integrity of microbial reduction and sterilizing grade membrane filters
Two integrity tests are recommended to confirm the integrity of microbial reduction and sterilizing grade membrane filters: Forward and Pressure Decay. The value of forward flow is linked to the results of the bacterial challenge test. The pressure decay value is derived from the forward flow value and the volume upstream of the housing.
These tests correlate to a set microbial removal or reduction level during the initial filter validation. As non-destructive tests, they may be used after sanitization and at the end of a production batch to show the filter assembly is integral. These tests are based on the same principles governing the gas flow through a wetted pore.
Integrity Test Values and Microbial Challenge
Forward flow test
- The pressure within the upstream volume of the filter housing is maintained at the filter-specific forward flow test pressure.
- The total gas flow, made up of diffusive flow through wet pores and bulk flow through open pores or defects, through the filter is measured by the test device upstream or downstream forward flow, which measures the flow required to maintain the test pressure.
Pressure decay test (also known as pressure hold)
- The pressure within the upstream volume of the filter housing is stabilized at the filter and housing-specific pressure decay test pressure.
- The test device upstream measures the total gas flow through the filter.
- Pressure decay measures the drop in the pressure.
Water for Intrusion Test (WIT)
- Water flow is measured through a hydrophobic filter and correlated to microbial retention.
Bacterial retention testing is the most sensitive integrity test for sterilization ability and microbial reduction. Testing for filter integrity can be destructive and may contaminate the filter with test bacteria, making it unsuitable for use. If properly correlated, non-destructive tests can indicate how well the filter retains bacterial challenges.
Practical Considerations When Performing Integrity Tests
| Selection of Integrity Test Fluid | Standard "Reference" Test Fluids
Water: Hydrophilic & Hydrophobic Filters
Alcohol/Water: Hydrophobic Filters
Process Fluids (derived values)
|
| Selection of Gas for Pressurization | Acceptable Test Gases:
Unacceptable Test Gases:
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| Temperature | The temperature should stay within 5 °C during an integrity test. Significant temperature changes can alter the fluid's gas diffusion. The recommended temperature range for integrity testing is 20 °C ± 5 °C (68 °F ± 9 °F). A 1 °C temperature change will cause an approximate 0.3% volume change due to its critical impact on gas pressure. |
| Upstream Volume | The upstream volume is an essential consideration for Pressure Decay tests. In applications where filters are effectively regenerated, their service lives will be dictated by their structure integrity. |
Palltronic® Compact Touch
Learn more about the next generation of pressure decay integrity test devices, designed specifically for Food & Beverage producers.