Filtration and fractionation are all about different particulate sizes, right? Guess again.

Munir Cheryan of the University of Illinois at Urbana-Champaign was present at the dawn of nanofiltration 20 years ago. Cheryan is a professor of food and biochemical engineering and author of the Ultrafiltration and Microfiltration Handbook, a book cited in scores of US patents involving filtration. Until 1985, "size was everything," the chemical engineer recalls. With nanofiltration, scientists could exploit the ionic charge of compounds of concern by employing membrane polymers that would cause a hydrophilic or hydrophobic reaction. In that way, elements could be passed through or blocked, depending on their desirability.