Filtration and ultrafiltration equipment and techniques

The spectrum of filtration separations runs from the millimeter scale (beach sand and activated carbon particles) using coarse fil- ters, to the angstrom scale (metal ions and gas molecules) using re- verse osmosis or gas separation membranes. Between there are mi- crofiltration (bacteria and emulsions), ultrafiltration (proteins, viruses, and colloids), and nanofiltration (sugars, herbicides, small organic molecules). In the analytical environment it is likely that membrane and filtration systems involving this entire spectrum will be used to provide high purity water, gases, reagents, and even special functions within instruments. In addition to these applica- tions, membranes and filters will often also be used in sample preparation and perhaps initial characterization. In this entry, we will discuss the principles, materials, and devices used to accom- plish coarse, micro- and ultrafiltration on the laboratory scale.