Filtration and ultrafiltration equipment and techniques

The spectrum of filtration separations runs from the millimeter scale (beac h sand and activated carbon particles) using coarse filters, to the angstro m scale (metal ions and gas molecules) using reverse osmosis or gas separat ion membranes. Between there are microfiltration (bacteria and emulsions), ultrafiltration (proteins, viruses, and colloids), and nanofiltration (suga rs, herbicides, small organic molecules). In the analytical environment it is likely that membrane and filtration systems involving this entire spectr um will be used to provide high purity water, gases, reagents, and even spe cial functions within instruments. In addition to these applications, membr anes and filters will often also be used in sample preparation and perhaps initial characterization. In this entry, we will discuss the principles, ma terials, and devices used to accomplish coarse, micro- and ultrafiltration on the laboratory scale.