Filter Integrity Tester
Comprehensive Guide to Bubble Point Testing
Sales Drawing IFP-161-0050 BUBBLE POINT TEST STAND 5 LITER
SALES DRAWING IFP-161-0002 BUBBLE POINT TEST STAND 2 REV A - New Address.pdf
Comprehensive Guide to Bubble Point Testing
Introduction:
It is fundamental to evaluate the integrity of the filter in sterile compounding and pharmaceutical filtration. The Bio-burden level underscores the importance of maintaining sterility in a sterilizing-grade filter. A single compromised filter can lead to issues such as contamination, loss of product, and violation of regulatory standards, which can have both financial and health-related repercussions. Therefore, it is essential to have a reliable method for assessing filter integrity. The Bubble Point Test is a standard analytical method for precisely evaluating filter integrity and ensuring sterility. The test employs the surface tension of a wetting liquid to determine if the filter is defect-free, thereby safeguarding the sterility of your product.
Bubble Point Test Overview:
The Bubble Point Test serves as a non-destructive, definitive method for verifying filter integrity. It measures the minimum pressure needed to overcome the capillary forces holding a wetting liquid with a known surface tension within the filter’s pore structure. This specific pressure point is known as the bubble point and indicates the filter's pore size and integrity. The bubble point equation mathematically describes the relationship between pore size and bubble point (1).
• D = Pore diameter
• 𝛾 = Surface tension of the wetting fluid
• 𝜃 = Contact angle between wetting fluid and filter surface
• ∆P = Pressure differential across the membrane
Note: The minimum Bubble Point value is not contingent on the type of membrane used. Instead, it is exclusively determined by the membrane's largest pore size and the surface tension of the flushing fluid. For instance, when flushing both a 0.2μm PES (Hydrophilic) membrane and a 0.2μm PTFE (Hydrophobic) membrane with a solution of 70% IPA and 30% water, the minimum bubble point value for both will be consistently 17.5 psi.
The test ensures that each filter is integral and free from manufacturing defects that could lead to filter bypass.
Quality Assurance: 100% Integrity Testing of Filters
In compliance to the highest manufacturing standards, every filter produced by Saint-Gobain and distributed by International Filter Products undergoes a 100% integrity test during its manufacturing process. This rigorous procedure, which employs the Bubble Point Test, ensures that each filter is free from defects or out-of-size pores, confirming our entire product range's reliability and high performance.
Acceptable Bubble Point Value:
Table 1: Acceptable Bubble Point Values for 0.2 µm membrane
|
Bubble Point Fluid |
0.2 µm PES – BP value |
0.2 µm PTFE – BP value |
||||
|
𝒑𝒔𝒊 |
𝑩𝒂𝒓 |
𝑴𝑷𝒂 |
𝒑𝒔𝒊 |
𝑩𝒂𝒓 |
𝑴𝑷𝒂 |
|
|
Water (*) |
50 |
3.445 |
0.345 |
NA |
NA |
NA |
|
60% IPA/ 40% H2O |
18 |
1.24 |
0.124 |
18 |
1.24 |
0.124 |
|
70% IPA/ 30% H2O |
17.5 |
1.21 |
0.121 |
17.5 |
1.21 |
0.121 |
(*) Water can be substituted by DI water, RO water, Purified Water, or Sterilized water.
Note: If the target pressure is met and no bubbles appear on the other side, the filter is effectively keeping the product sterile.
Special Considerations for PTFE Membranes: It is imperative to recognize that PTFE–hydrophobic membranes exhibit hydrophobic characteristics. Therefore, the Bubble Point Test for PTFE membranes requires the use of an alcohol-based wetting solution, rendering DI water unsuitable for this application.
Advantages of Using 70% IPA or 60% IPA:
· Enhanced Efficiency: IPA solutions ensure faster and more thorough removal of medications from the filter membrane compared to DI water.
· Safety and Operational Efficiency: Utilizing IPA results in an acceptable bubble point value 50% less than f DI water. This means that the maximum operational pressure within the device decreases by half when using IPA, significantly boosting the safety of the procedure.
· Versatility with Membrane Types: While PTFE membranes, due to their hydrophobic nature, require either 70% or 60% IPA for flushing, other materials like PES membranes or PP media can be flushed using both DI water and IPA solutions. This versatility ensures that IPA can accommodate a wide range of membranes and media, allowing labs to streamline their resources and eliminate the need for multiple flushing solutions.
Process Overview: A Step-by-Step Protocol
Step 1: Selection of flushing fluid
To begin, select a wetting solution according to the membrane and application requirements:
Option A: A mixture of 70% Isopropanol Alcohol (IPA) and 30% Deionized (DI) Water. This is particularly recommended due to its widespread availability in pharmaceutical settings.
Option B: A mixture comprising 60% Isopropanol Alcohol (IPA) and 40% Deionized (DI) Water. This offers a viable alternative to Option A.
Option C: 100% Deionized (DI) Water. This requires the highest acceptable pressure point, making the process time-consuming and arduous.
Step 2: Flushing and Wetting the Membrane
Utilizing the selected solution, perform a flush of the filter system. This action accomplishes two key objectives:
· Flush and replace any previously filtered substances from the membrane pores.
· Wetting the membrane pores in preparation for the pressurized air test.
Table 2 outlines the designated flushing volume ranges corresponding to each filter size offered by International Filter Products.
Table 2: Pre-Bubble Point Flushing Volume
|
Filter Series |
Filtration Area |
Pre-BP Flushing Volume |
|
D25C |
4.6 cm2 |
30 mL - 60 mL |
|
D40C |
10.6 cm2 |
40 mL- 80 mL |
|
D50C |
15.9 cm2 |
50 mL -100 mL |
|
D65R |
26 cm2 |
60 mL - 150 mL |
|
D90R |
60 cm2 |
100 mL - 300 mL |
|
JKP |
260 cm2 |
200 mL - 500 mL |
|
MKP |
500 cm2 |
300 mL -600 mL |
|
Filter Series |
Filtration Area |
Pre-BP Flushing Volume |
|
SKL/SKV- H SIZE |
720 cm2 |
500 mL – 1 L |
|
SKL/SKV- S SIZE |
1,380 cm2 |
600 mL - 1.2 L |
|
SKL/SKV- L SIZE |
2,600 cm2 |
1L - 2L |
|
SKL/SKV- K SIZE |
5,200 cm2 |
1.5L - 2.5L |
Step 3: Pressurizing the membrane [If performed manually]
To execute a successful Bubble Point Test, it is essential to adhere to the following detailed procedure:
· Connection: Ensure that the pre-flushed filter is connected to a suitable air source if it isn't already.
· Outlet Extension: Attach a length of hose or tubing to the filter's outlet.
· Submersion for Bubble Detection: Immerse the free end of this tubing into a water container; this will serve as your bubble detection mechanism.
· Initial Pressure Increment: Begin by gradually increasing the air pressure in increments of 5 psi.
· Critical Attention Zone: As you approach the bubble point range—or a pressure 10 psi less than the expected bubble point—be particularly attentive.
· Fine-Tuned Pressure Adjustment: Within this critical range, adjust the pressure more finely, in increments of 1 psi, while closely observing for the appearance of bubbles in the water.
· Successful Test Indication: If the bubble point threshold is surpassed without the emergence of bubbles, the test is deemed successful, confirming that the membrane has maintained its integrity throughout the process.
By following these steps meticulously, you can reliably validate the performance and integrity of your filter membrane.
Essential Guidelines and Recommendations:
· Flush the medication as early as possible after the use. Dry medication on the membrane is more difficult to flush.
· Pulsing during the flushing procedure helps to flush the membrane more effectively.
· Diffusive flow of bubbles cannot be considered as a failed integrity test. Allow 10-15 seconds to stabilize the diffusive flow.
Types of Integrity Test Results:
Understanding the range and implications of integrity test results is crucial for accurately interpreting outcomes. Results generally fall into the following three categories:
· Pass: This occurs when the bubble point is within specification and the typical range. For example, a filter with a minimum bubble point of 50 psi may yield 52 to 62 psi results. In such cases, confidence in the filter's integrity is high.
· Gross Failure: This scenario arises when a high gas flow at low pressure is indicative of a non-integral filter. This kind of failure can happen if the filter is damaged due to factors like high differential pressure, physical impact, or excessive heat. Such conditions necessitate troubleshooting and retesting, although the probability of the retests confirming the filter's integrity is low.
· Marginal Failure: Characterized by test results slightly falling short of the specifications. For instance, a bubble point might be 48 psi when the specification is 50 psi. These marginal failures usually relate to factors impacting capillary forces, such as low surface tension, poor wetting, or testing errors. Upon observing marginal results, troubleshooting and retest procedures should be applied, and there is a high likelihood that retests will confirm the filter's integrity.
· Invalid Test: Results within the specifications but outside the typical range suggest an issue with test execution. For example, a bubble point result of 80 psi when the specification is ≥ 50 psi may indicate an improperly closed valve. While rare, such cases require personnel to retest and evaluate the invalid outcomes.
By understanding these categories, professionals can better assess the reliability and performance of filter systems.
Key Factors of Low Bubble Point and Test Failures
· Inadequate Flushing: The most frequent reason for an apparent test failure is often incomplete or improper flushing of the membrane. We strongly recommend flushing with a sufficient volume of the appropriate solution. If a lower bubble point value is observed, it's advisable to re-flush the membrane and conduct the test anew.
· Chemical Compatibility Issues: If the filter membrane is chemically incompatible with the medication or substance being filtered, the integrity of the membrane could be compromised, leading to a lower bubble point value.
· Over-pressurization: Exceeding the recommended pressure limits can result in membrane damage. Saint-Gobain filters can withstand a maximum pressure of 80 psi—the industry standard. However, we highly caution against exceeding 68 psi during the test. Repeater pumps can inadvertently exert pressures exceeding 100 psi if not carefully monitored.
Bubble Point Value Analysis:
Saint-Gobain membranes represent the pinnacle of innovation, setting a new benchmark for precision and advanced sterility in the market. When flushed with 100% water, a 0.2μm sterilizing grade Saint-Gobain membrane has a minimum Bubble Point value of 50 psi. In contrast, our competitors' average bubble point values for a 0.2μm micron filter fall within the 53 to 55 psi range, indicating an average pore size of approximately 0.185μm to 0.175μm.
Remarkably, Saint-Gobain membranes consistently exhibit a significantly higher Bubble Point average of 60 psi, corresponding to an average pore size of around 0.155μm. This exceptional performance virtually eliminates the risk of contaminant bypass, ensuring the utmost product purity.
Additional Advantages of a Tighter Membrane with a Higher Bubble Point Value:
· Superior Bio-burden Control: Outstanding performance in bacterial challenge tests.
· Enhanced Pore Tightness: Allows for cleaner, more efficient filtration.
· Reduced Endotoxin Levels: Lower figures signify better sterility and purity.
· Optimized Filtration Quality: Enhanced particle removal for a cleaner end-product.
This exceptional performance virtually eliminates the risk of contaminant bypass, reducing the possibility of contamination to zero percent.
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