Field-flow fractionation

Field-flow fractionation (FFF) is a family of instrumental techniques that separates and characterizes macromolecules, colloids, and particles (macromaterials) on an analytical scale (Colfen and Antonietti, 2000; Schimpf et al., 2000). As illustrated in Fig. 1, the FFF channel has a ribbon-shaped geometry, typically with length 30-50 cm, breadth 1-3 cm, and thickness 0.005- 0.025 cm. Because of the high aspect ratio between breadth and thickness, liquid that is pumped through the channel flows in a laminar fashion, with a velocity profile that varies across the thin (x) dimension. A field is applied external to the channel in order to force analyte into the slower flow streams near one wall. The resulting velocity of the analyte through the channel depends on its interaction with the field, and therefore, on physicochemical properties that govern that interaction. Those physicochemical properties vary with the nature of the applied field, but always include the size of the analyte, because size determines the ability of analyte to reach the faster moving flow streams away from the accumulation wall.