Air-Water Binary Gas Integrity Test for Sterilizing and Virus Filters.

Abstract

To ensure that sterilizing and virus removal filters are free of defects, an integrity test is often conducted both before and after use of the filters. In the commonly used air-water diffusion integrity test, pressurized air is applied to the water wetted filter and the air flow rate across the filter is measured. A flow rate above a specified limit indicates a leak through the filter. The sensitivity of the test is limited by the level of background noise (integral flow rate) relative to the leak signal (excess flow rate). An enhancement to the air-water diffusion test is introduced here in which the sensitivity of the test can be improved by measuring the composition of the diffused gas. Oxygen permeates through water faster than does nitrogen, so the permeating gas will be enriched in oxygen. Compared to the flow rate, which can span a range of values for integral filters, the integral oxygen concentration is well defined, so even small deviations from the expected concentration signal a leak. Because air and water are used as the test materials, the developed approach achieved higher sensitivity without sacrificing the convenience, safety, and environmentally friendly aspects of the air-water diffusion test.