Asymmetric flow field flow fractionation


Asymmetrical flow field-flow fractionation is a fractionation method that is used for the characterization of nanoparticles, polymers and proteins. The theory for AF4 was conceived in 1986 and was established in 1987. It is a separation technique based on the theory of field flow fractionation. AF4 is distinct from FFF because it contains only one permeable wall so the cross-flow is caused only by the carrier liquid. The cross-flow is induced by the carrier liquid constantly exiting by way of the semi-permeable wall on the bottom of the channel. It has been used to characterize condensed tannins oxidation.

Operational procedures

The AF4 experiment can be separated into three stages:
1. Sample Injection
2. Sample focusing

3. Fractionation

Applications

Asymmetrical flow field flow fractionation is nowadays a common and state-of-the art method for fractionation and separation of macromolecules and particles in a suspension. More commonly, HPLC would be used for liquid separations for molecules up to 10 kDa and nanoparticles up to 10 nm. AF4's application are flexible for many analytical conditions where a common method would be unable to properly separate the desired particles. For macromolecules and nanoparticles AF4 is an alternative method especially when the static phase in columns interacts with the sample. It has also been used to study aggregation of particles in a solution.