Diffusion and Bubble Point Testing of Microporous Cartridge Filters: Preliminary Results at Production Facilities

W. P. Olson, E. D. Martinez and C. R. Kern


“Durapore,” “Sartobran,” and “Ultipore Nylon 66” membrane filter cartridges, rated by the manufacturers at 0.2-μm poresize, removed all Pseudomonas diminuta ATCC 19146 from saline lactose broth and all bacteria and molds from naturally-contaminated trypticase soy broth. After autoclaving of the Durapore and Sartobran cartridges, their bubble points increased by approximately 5 and 15 psi, respectively, whereas the Ultipore Nylon 66 cartridge bubble points did not change appreciably. Because the pre-autoclave bubble points of the Durapore and Sartobran made a satisfactory diffusion test at 80% of the post-autoclave bubble point difficult or impossible to do, these were best diffusion tested at 30 psi. However, the Ultipore Nylon 66 could be diffusion-tested at 40 psi. The diffusion test proved to be an unambiguous measure of filter integrity, but the bubble point test also was deemed essential to the proper characterization of 0.2-μm poresize membrane filter cartridges. The Ultipore Nylon 66 cartridges, rated by the manufacturer at 0.45 μm, tolerated pressures in excess of 50 psi in the filtration of large volumes parenterals. These cartridges were diffusion tested at 25 psi. Bubble point analysis was considered less critical for the filters used with large volume parenterals than for the 0.2-μm poresize filters.

  • Received February 13, 1981.
  • Accepted May 15, 1981.

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