Difference between revisions of "Field-Flow fractionation (FFF)"

<onlyinclude>'''Field-Flow Fractionation (FFF)''' is a family of high resolution separation techniques especially applicable to macromolecules colloids and particles, and shares the most common likeness with liquid [[chromatography]] (LC). The mechanism for separation, however, does not involve interactions with a stationary phase used in LC methods. Instead, a field is applied normal to a laminar flow through a narrow channel, which reslts in a parabolic flow profile, separating different analytes into distinct regions of the velocity profile. The analytes can be fractionated according to their physicochemical properties such as charge, chemical composition, density, molar mass, and size. Beside analytical purposes the FFF can also be utilised for preparative purposes.

Suitable feedstocks are heterogeneous mixtures of different substances in form of dilute suspensions (solids in liquid). Depending on the applied process and technology solids can be usually separated between the nm-µm range. The FFF is usually applied to separate cells, different kind of nanoparticles, polymers, and proteins for analytical and preparative purposes.

Different variants of the FFF are available, which includes Asymmetric flow FFF (AF4), centrifugal FFF, electrical FFF (EFFF), split flow thin-cell fractionation (SPLITT), and thermal FFF (TF3). Depending on the applied technology particles can be separated in dependence of different physicochemical properties.

This technology combines the FFF with an electrical field as additional separation force. An electrical voltage is imposed between the top and bottom walls. Charged particles migrate toward either wall according to their electrophoretic mobility, which is determined by their sizes and charge densities, and undergo different flow velocity.<ref>{{Cite book|author=T. Okada|year=2007|section_title=Field Flow Fractionation: Electric Fields|book_title=Encyclopedia of Separation Science|publisher=Academic Press}}</ref> Besides the separation based on particle size this method adds the capability to separate particles/molecules in dependence of their charge. EFFF is well suited to the fractionation of proteins and measuring protein adsorption on to surfaces.<ref>{{Cite book|author=R. Hecker, H. Colfen|year=2000|section_title=PROTEINS/Field Flow Fractionation|book_title=Encyclopedia of Separation Science|publisher=Academic Press}}</ref>

In Split flow thin-cell fractionation (SPLITT) earth's gravitational force is used to separate different sized particles (usually in µm-range). Usually the suspensions are introduced into the top of a separation channel while a carrier liquid is pumped into the channel from the bottom. The separation of different sized solids occurs along the channel induced by earth's gravity. Two outlets (one at the channel bottom, one at the channel top) at the end of the channel separates the particles into a larger and smaller fraction while the cut-off can be controllel via the channel flows.