Flow Field-Flow Fractionation

In flow field-flow fractionation (FlFFF), the field is a crossflow of carrier liquid perpendicular to the usual channel flow. The field strength is thus determined by the flow rate of this crossflow.

A porous frit mounted in the lower block, allows the crossflow to exit through the accumulation wall. A membrane is usually used to prevent loss of sample. The particles or molecules will elute in the order of decreasing diffusion coefficient (i.e. increasing hydrodynamic diameter).

Theory

In FlFFF the retention parameter l is related to the diffusion coefficient D by:

where D is the diffusion coefficient (cm²/s), V_o is the channel void volume (mL), V is the crossflow rate (mL/s) and w is the channel thickness (cm)

In case of macromolecules, the diffusion coefficient can be related to molecular weight using molecular weight standards and the empirical relationship:

where M is the molecular weight, and A and b are constants for a particular sample-solvent system.

Applications of FlFFF:

FlFFF can be used for separation of particles in the range from less than one nanometre to tens of micrometers. Using a suitable calibration, it also has the ability to yield the molecular weight distributions. Water soluble polymers, proteins, biological samples, humic substances and clay minerals are among the samples that can be separated by FlFFF.

Applications of FlFFF at the WSC:

• Characterization of humic substances
• Monitoring the performance of ultrafiltration membranes
• Size and chemical characterization of pulp and paper mill effluent
• Separation of clay minerals

Further Reading:

• Giddings, J. C. (1988). "Field-Flow Fractionation" C   E News, 66: 34-45.
• Giddings, J. C., Yang, F.J., and Myres, M.N. (1977). "Flow Field-Flow Fractionation as a Methodology for Protein Separation and Characterization" Analytical Biochemistry, 81: 395-407.
• Beckett, R., Zhang J., Giddings C. (1987). "Determination of Molecular Weight Distributions of Fulvic and Humic Acids, using Flow Field-Flow Fractionation" Environmental Science and Technology, 21: 289-295.
• Beckett, R., Wood, F.J. and Dixon, D. (1992). "Size and Chemical Characterization of Pulp and Paper Mill Effluents by Flow Field-Flow Fractionation and Resin Adsorption Techniques" Environmental Technology, 13: 1129-1140.
• Beckett, R. and Hart, B.T. (1993). Use of Field-Flow Fractionation Techniques to Characterize Aquatic Particles and Macromolecules. in Environmental Particles. J. Buffle and H.P. Van Leeuwen (ed) , Lewis Publishers. 2: 165-205.