Critical influences of particles, pores, and prefilters in sterilizing filtration.

Sterilizing filtration process variables can cause unpredictable results and post-filtration integrity test values that are not representative of those obtained during validation of the filtration process. This paper discusses several points to consider in sterilizing filtration designed to assure the validated process is robust and consistently yields a sterile filtrate. These points include pore- and particle-size distributions, the use and choice of prefilters, pore configuration, and the use of redundant (serial) filtration.

The mechanics of removing organisms by filtration: the importance of theory.

Very often, the concept of filtration is only considered in terms of sieve retention, which can sometimes be misleading. In this review of the adsorptive particle-capture mechanism, the authors aim to familiarize the filtration practitioner with the possible optimisation of particle retention by the manipulation of factors such as ionic strength, osmolarity, temperature and the use of polymeric filters.

Modus of filtration.

Experience teaches that particles larger than the pores of a filter cannot negotiate its passage. Other retention mechanisms are less obvious than sieve retention or size exclusion. They are electrical in nature, and find expression in the bonding alliances that mutually attract (or repel) filters and particles. The influence of hydrogen bonds, of van der Waals forces, of hydrophobic adsorptions, and of transient polarities on particle retentions are set forth in terms of the double electrical layer concept that also governs colloidal destabilizations. The origins of differences in membrane porosities is explained, as also the importance of the filtration conditions. The singularity of the particle-fluid-filter relationship on organism and/or pore size alteration is stressed.