Separation based on the retention and elution of macromolecular, colloidal, and particulate matter achieved by the combined action of the non-uniform flow speed (velocity) profile of a carrier fluid (mobile phase) and a physical force field (e.g. gravitational, centrifugal, electrical) applied at right angles to a thin (\(\pu{0.05 mm}\) to \(\pu{0.5 mm}\)) channel (see figure).

Basic principle of field-flow fractionation.
Notes: - Although similar to liquid chromatography, FFF requires no stationary phase, so the separation channel contains no packing material and only physical interactions are involved in the separation process.
- FFF is applicable to the fractionation and characterization of colloidal and solid particles, polymers, and biological cells in the size range from \(\pu{1 nm}\) to \(\pu{50 \upmu\!m}\).
- The sample mass injected is usually less than \(\pu{1 mg}\) to avoid overloading.
Source:
PAC, 2017, 90, 181. 'Terminology of separation methods (IUPAC Recommendations 2017)' on page 220 (https://doi.org/10.1515/pac-2017-0111)