Comparison of the fractionating methods Analytical Ultracentrifugation (AUC) and Field-Flow Fractionation (FFF)


Analytical Ultracentrifugation (AUC)

Field-Flow Fractionation (FFF)


Sedimentation of particles subject to strong centrifugal fields opposed by diffusion. Monitoring of sedimentation with optical systems.

Migration of particles exposed to variable fields opposed by diffusion from the accumulation wall. Elution occurs in dependency from the distance to the accumulation wall.


various optical systems detect concentration profiles during sedimentation. (Time and local resolution)

Eluate is examined with variable detectors.


Fractionation by mass, size and density – all properties may be distributed.

Experiments are very versatile and can be optimized in respect to the property in question.

Resolution of particle sizes is in the Ångström range.

Simultaneously, spectroscopic properties are measured.

Arbitrary solvents and systems are applicable.

Very high resolution is achieved, assuming simple geometry and constant particle density.

Short experimental times are required.

Diffusion coefficient distributions are independent of particle density.

Variable fields can be applied: temperature, gravity, flow, electric fields...

Low costs for installation and maintenance


No fractionation occurs when density and size compensate to lead to identical sedimentation constants. This case is most improbable and can be eliminated by choosing a different solvent.

High installation costs, high need for interpretation of the data.

Strong deviations from expected results for other particle geometries but spherical.

Interactions with the membrane possible with F-FFF.

The set of variables is limited to D and related properties.

Target properties

sedimentation constant, molecular mass, diameter, diffusion constant, density and others

diffusion constant

Reasonable application

Spherical particles, if more properties than size are relevant. For non-spherical systems, FFF is no alternative.

Spherical particles, if only size is relevant