Filter tests bubble point test

The tests described so far have all been challenge tests, in which a known suspension is fed to a test filter. The bubble point test, on the other hand, measures a characteristic of the filter medium without use of particles. 

Bubble point test A test to determine the maximum pore si2e opening of a filter. Buffer A solution or liquid whose chemical makeup neutralizes acids or bases without a great change in pH. 

Perform a pressure hold test with the sterilized filter. Perform the filtration of the product to be sterile filtered using normal production conditions. After the filtration step, the filter should be tested again with the bubble point test. 

The bubble point test is a popular single-point physical integrity test for disc filter membranes based on Eq. (21). A fdter medium is wetted with a liquid, and test gas pressure is slowly raised until a steady stream of bubbles appears from a tube or hose attached to the downstream side of the filter and immersed in water (Fig. 9). The pressure at which the bubbles first appear is recorded as the bubble point and is related to the largest pores in the fdter medium. A pore size can be calculated from Eq. (21) however, it must be realized that the bubble point test does not measure the actual pore size, but only allows correla-... 

The bubble point test, while popular, has some deficiencies that must be realized. First, there is variation in the operator detection of the test end point that is, the first appearance of gas bubbles rising in the liquid. Some operators are able to see smaller bubbles than others. In a recent study, a panel of seven observers recorded the initial detection of a steady stream of air bubbles rising from a capillary held under water as the air pressure was gradually increased. The observers, who had received different degrees of training, identified the simulated bubble point as occurring at air flows of 5 to 50 mL/min corresponding to air pressures of 34 and 38 psi, respectively, for a 90-mm disc filter membrane [56]. 

Figure 7.8 Correlation of P. diminuta microbial challenge and bubble point test data for a series of related membranes [6]. Reprinted from T.J. Leahy and M.J. Sullivan, Validation of Bacterial Retention Capabilities of Membrane Filters, Pharm. Technol. 2, 65 (1978) with permission from Pharmaceutical Technology, Eugene, OR...

ASTM F316-03 Standard test methods for pore size characteristics of membrane filters by bubble point and mean flow pore test. 

ASTM F 316-86, Standard test method for pore size characterisation of membrane filters by bubble point and mean flow pore test. Annual Book of ASTM Standards, Vol. 10.05, 1990 (originally published as F316-70, last previous edition F316-80). 

The integrity of sterilizing fillers is most often validated and routinely monitored by nondestructive methods. The U.S., European, and U.K. guidelines on sterile filtration refer to four methods of integrity measurement filtration flow rate, bubble point tests, diffusion (forward flow) tests, and pressure hold tests. Each of these has its uses in determining that routinely used filters are per-forming to the same standards as those validated for the particular products and processes. 

Bubble Point Test Theoretical aspects of the bubble point lest have been addressed in Section 1 above. The bubble point test predicts the performance of a filter by detecting the differential pressure at which a fluid is displaced by gas from the pores of a wetted filter, thus allowing capillary flow of the gas through the filter. 

The deficiencies and nonidealities that occur in bubble point testing should not be taken as contraindications of the usefulness of the method for in-process nondestructive filter integrity testing. It is in fact an extremely valuable in-process test. Its limitations should be understood and its value confined to comparing one filter with another of the same type. 

In practice the test is done as almost a mirror image of the bubble point test. The filter housing is filled completely with water, and pressure on the upstream side is increased incrementally until water flow is seen on the dow n-... 

The integrity of the filter should be checked by an appropriate method such as a bubble point test immediately after each use (it may also be useful to test the filter in this way before use). The time taken to filter a known volume of bulk solution and the pressure difference to be used across the filter should be determined during validation and any significant differences from this should be noted and investigated. 

Every day, before the filtration system starts operating, two tests (diffusion test and bubble point test) should be carried out to check the integrity of the damp membranes and to inspect the watertight seals, once the filter has cooled down. Details are given in the membrane manufacturer s instructions. These inspections are indispensable to ensure that the filter media operate at optimum efficiency (Table 11.10). 

Since the main function of any filter is the removal and separation of impurities, and the filters are rated in many different ways, it is inevitable that many tests are available to substantiate these ratings. The tests include the bubble point test used to establish the mean filter rating and the multi-pass test which provides the beta ratio of the hydraulic and lubrication filters. 

Bubble point tests are used extensively in detminming the largest and mean pore, in new and recycled filters. Simultaneously, the integrity of the filter can also be estabh ed [Johnston, 1986] in detecting wear and tear of the filter bric. 

Bubble Point Test. This is a widely used test to establish the largest pore size available in the filter under test. It is also regarded as a standard integrity and quality control check... 

The in-process controls for sterile ear drops are the same as for non-sterile ear drops, with extra controls for the microbiological quality. These could be the bubble point test on filters and parameters of the sterilisation process. 

The integrity of membrane filters with a pore size of 0.2 and 1.2 pm should be verified using a bubble-point test after use as an in-process control. During this test a 0.2 pm membrane filter should resist the air pressure produced by moving the plunger over 80-85 % of the total syringe volume and in the case of a 1.2 pm membrane filter over 50-60 % without continuous bubble formation on the opposite of the membrane (see also Sect. 30.6.5). 

Integrity of the filter device by a bubble point test or forward-flow-test (see Sect. 30.6.5) pH of aqueous solutions... 

As described above, a test fluid (usually water) is retained by the filter membrane material by surface tension and capillary forces). This adhesion is, amongst others, dependent on the pore size of the filter. In the bubble point test air pressure is applied to the moistened filter and it is observed at which pressure air bubbles are formed on the sterile side of the filter. The pressure at which the first bubbles are formed is called the bubble point. At this moment, the liquid is pushed out of the largest pores. 

In most pharmacies a simplified bubble point test is performed. In this test, a moistened 0.2 pm filter should be able to resist the pressure of a syringe filled with air that is compressed down to 15—20 % of its original volume. For a... 

When a test gas (for example ambient air) is applied over a water moistened filter, just below the pressure level of the bubble point, test gas diffusion will occur through the water in the wetted membrane filter. This diffusion happens in all water filled pores, not only in the largest. This principle is the basis for two tests, which use different approaches to measure gas diffusion the pressure hold test and the diffusive-flow (forward flow) test. Other names for the same principle tests exist. These tests are performed at a pressure of about 80 % of the theoretical bubble point pressure of the filter. It is important that the largest pores are still filled with liquid. In this phase, diffusion occurs more or less linearly with the pressure drop over the... 

Newton DW (2008) Membrane-filter bubble-point test. Am J Health Syst Pharm 65 2210-2212... 

The bubble point test is based on the fact that, for a porous filter medium, immersed in and thoroughly wetted by a specific liquid, the pressure required to force a gas bubble through a pore is inversely proportional to the diameter of the pore. In practice, this means that the pore size of a filter element can be established by wetting the element completely with the liquid and measuring the pressure at... 

A typical rig for the bubble point test is shown in Figure 1.18. The sample of filter medium is immersed in a suitable liquid (often f-propyl alcohol), and air is forced into the interior of the sample from a reservoir until the first bubble is seen, at which point the air pressure is recorded. 

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