Field-flow fractionation resolution

Biomolecule Separations. Advances in chemical separation techniques such as capillary zone electrophoresis (cze) and sedimentation field flow fractionation (sfff) allow for the isolation of nanogram quantities of amino acids and proteins, as weU as the characterization of large biomolecules (63—68) (see Biopolymers, analytical techniques). The two aforementioned techniques, as weU as chromatography and centrifugation, ate all based upon the differential migration of materials. Trends in the area of separations are toward the manipulation of smaller sample volumes, more rapid purification and analysis of materials, higher resolution of complex mixtures, milder conditions, and higher recovery (69). 

Some of these fractionation problems can be ameliorated by the use of the relatively new technique of field-flow-fractionation (FFF). Its advantages include high-resolution separation and sizing of particulate, colloidal and macromolecu-lar materials covering 105-fold range from about 10 3 to 1()2/rm (see Chapter 8). 

Clearly, sedimentation FFF is a separation technique. It is an important member of the field-flow fractionation (FFF) family of techniques. Although other members of the FFF family (especially thermal FFF) are more effective for polymer analysis, sedimentation FFF is advantageous for the separation of a wide assortment of colloidal particles. Sedimentation FFF not only yields higher resolution than nearly all other particle separation techniques, but its simple theoretical basis allows a straightforward connection between observed particle migration rates and particle size. Thus size distribution curves are readily obtained on the basis of theoretical analysis without the need for (and uncertainties of) calibration. 

Comparison of Polymer Resolution in Thermal Field-Flow Fractionation and Size Exclusion Chromatography, J. J. Gunderson and J. C. Giddings, Anal. Chim. Acta, 189, 1 (1986). 

Commercially available fractionation methods include hydrodynamic chromatography (HDC), field flow fractionation (FFF) and disc centrifugation (DSC). One advantage of fractionation methods over nonfractionation methods is that the particles are separated physically according to size, prior to detection, which allows much higher resolution in determining the size distribution [40]. 

Field-flow fractionation is a family of high-resolution techniques capable of separating and characterizing colloids and macromolecules. In normal FFF, the particles form a Brownian-motion cloud that extends a short distance into the channel. Separation is possible because the solvent flows at different velocities at various points within the channel. The smaller particles, whose cloud protrudes out into the faster laminae, are transported more rapidly than the larger particles, so... 

Anger, S., Mehnert, W., Caldwell, K.D. and Muller R.H. (1998) High resolution determination of adsorption layer mass on particles by sedimentation field-flow fractionation. Proc. Second World Meeting APGI/APV, Paris, 643-644. 

Particle-size and mass distribution curves, along with information on particle porosity, density, shape, and aggregation, can be obtained for submicrometer- and supramicrometer-size silica materials suspended in either aqueous or nonaqueous media by field-flow fractionation (FFF). Narrow fractions can readily be collected for confirmation or further characterization by microscopy and other means. Among the silicas examined were different types of colloidal microspheres, fumed silica, and various chromatographic supports. Size distribution curves for aqueous silica suspensions were obtained by both sedimentation FFF and flow FFF and for nonaqueous suspensions by thermal FFF. Populations of aggregates and oversized particles were isolated and identified in some samples. The capability of FFF to achieve the high-resolution fractionation of silica is confirmed by the collection of fractions and their examination by electron microscopy. 

Source From Resolution of colloidal latex aggregates by sedimentation field-flow fractionation, in J. Chromatogr. Copyright Elsevier Science PubUshers B.V. 

Stolpe, B. HasseUov, M. Andersson, K. Turner, D.R. High resolution ICPMS as an on-hne detector for flow field-flow fractionation multi-element determination of coUoidal size distributions in a natural water sample. Anal. Chim. Acta 2005, 535 (1-2), 109-121. 

Field-flow fractionation (FFF) is a reliable technique for separation and characterization of colloids and polymers. It is a dynamic separation technique based on the differential elution of the sample constituents by a laminar flow, in a flat ribbon-like channel, according to their sensitivity to an external field applied in the perpendicular direction to that of the flow. Resolution in the FFF system is a function of the time allowed to equihbrate (or relax) the sample within the channel under the force field, with the mobile phase not flowing prior to fractionation. 

The study of the interfacial phenomena between the channel wall and the colloidal suspension under study in sedimentation field-flow fractionation (SdFFF) is of great significance in investigating the resolution of the SdFFF separation method and its accuracy in determining particles physicochemical quantities. The particle-wall interactions in SdFFF affect the exponential transversal distribution of the analyte and the parabolic flow profile, leading to deviations from the classical retention theory, thus influencing the accuracy of analyte quantities measured by SdFFF. Among the various particle-wall interactions, our discussion focuses on the van der Waals attractive and electrostatic repulsion forces, which play dominant roles in SdFFF surface phenomena. 

The surface phenomena in SdFFF are the main factors influencing the accuracy of colloidal properties measured by field-flow fractionation. It is, therefore, important to point out the interactions between the colloidal particles and the SdFFF channel wall in order to correct the separation resolution and/or the analyte characterization. 

This entry provides an overview of thermal field-flow fractionation (ThFFF) and its application to polymer and particle analysis. The separation mechanism is described and contrasted with that in size exclusion chromatography (SEC). The two techniques are somewhat complementary. Thus, SEC typically provides superior resolution of low molecular weight (M) polymers (M <100,000 Da), while ThFFF excels in the separation of high-molecular weight polymers (M >100,000 Da), gels, and particles. 

Gunderson, J.J. Giddings, J.C. Comparison of polymer resolution in thermal field-flow fractionation and size-exclusion chromatography. Anal. Chim. Acta 1986,189,1. 

In field-flow fractionation (FFF), like chromatography, retention and resolution are affected by temperature. For calibration curves to be as precise as possible, or in the case of ThFFF, to universally apply a calibration curve to channels in different laboratories, it is important to closely control the temperature. In ThFFF, the analyte is typically compressed into a layer very close to the cold wall. Therefore, the temperature of the analyte is usually within a few degrees of the cold wall temperature. Consequently, the retention of a given component from one run to the next, or from one instrument to another, will be identical only if the cold wall temperatures are identical. 

MFFF Magnetic Field-Flow Fractionation RRHT Rapid Resolution High Throughput... 

Giddings et have examined a new method for polymer analysis, termed Field Flow Fractionation (FFF). In this technique a flow profile of parabolic shape is set up in a thin flow channel by pumping solvent through it. At the same time some form of field (usually a thermal gradient) is applied across the flow channel. If a polymer is injected into the field with no flow then the field causes it to concentrate at one side of the flow channel. This concentration is opposed by diffusion so that a concentration profile is set up across the field, in which the molecules are resolved according to their thermal diffusion coefficients and hence their molar masses. When the flow is applied the polymer is eluted with molar mass resolution. As yet the method has not shown anything like its theoretical resolution but preliminary results are very interesting. 

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