ABSTRACT
Sterilizing-grade filtrations and aseptic methods are increasingly common for the processing of injectable solutions. In the filtration of liquids, particles larger than the largest pores of a membrane filter remain on the filter surface. Particles and organisms smaller than the pore size may pass into the void volume below the filter surface; many fine particles, on impacting the filter matrix, are retained. Vent filters usually operate at atmospheric pressure, which, for most hydrophilic membrane filters with small pores, is insufficient to displace free water in the pores. The most common fibrous vent filters are of fine borosilicate glass. They are somewhat hydrophilic and are kept dry by heating the filter holders, usually with high resistance heat tapes. Where sterilizing filtration is done in-line with a filling line, it is essential that the autoclave-sterilized final filter be preceded by an identical but nonsterile filter.
