Field-Flow-Fractionation (FFF) is a chromatography-like analytical technology to separate molecules and particles ranging from a few nanometers to a few micrometers (respectively Mw = 1x103 – 1x108 g/mol). Asymmetric Flow Field-Flow Fractionation (A-F-FFF or AF4) belongs to the group of Field-Flow Fractionation methods. AF4 is a relative new and efficient method for rapid fractionation and high resolution characterization of various polymers as well as nanoparticles and –capsules as investigated in our department. Separation in AF4 occurs in a thin flow channel. The channel flow (in our case we use water as a solvent) carries the sample through the channel. Due to this channel flow a parabolic flow profile occurs, as shown in Figure 1. Perpendicular to this channel flow a second flow, the cross-flow, generates a force field, which drives the molecules or particles in the direction of the channel bottom. Smaller particles will diffuse back into the channel further than larger particles because of their larger diffusion coefficients. As a result various components are arranged into regions of different flow velocities and therefore smaller molecules or particles are eluted faster than larger components.
Figure 1: Separation principle of AF4
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