Field flow fractionator

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). 

Field-Flow Fractionation. Field-flow fractionation is a general name for a class of separation techniques that fractionate a particle population into groups according to size. The work in this area has been reviewed (59). 

Fig. 9. Principles of field-flow fractionation (a) sample equilibrium position before flow is initiated, (b) fractionated sample after flow initiation, and (c) a...

Fig. 10. Centrifugal sedimentation field-flow fractionation equipment deposits particles along the circumference of the disk by size. The fluid enters and...

Among the techniques employed to estimate the average molecular weight distribution of polymers are end-group analysis, dilute solution viscosity, reduction in vapor pressure, ebuUiometry, cryoscopy, vapor pressure osmometry, fractionation, hplc, phase distribution chromatography, field flow fractionation, and gel-permeation chromatography (gpc). For routine analysis of SBR polymers, gpc is widely accepted. Table 1 lists a number of physical properties of SBR (random) compared to natural mbber, solution polybutadiene, and SB block copolymer. 

Currently, there are several molecular weight separation techniques, such as OTHdC, PCHdC, SEC, thermal field flow fractionation (ThFFF), and sedimentation field flow fractionation (SdFFF). The molecular weight separation range... 

SEC, size exclusion chromatography OTHdC, open tubular hydrodynamic chromatography PCHdC, packed column hydrodynamic chromatography ThFFF, thermal field flow fractionation. 

Techniques which seem less suitable for routine size analysis are (1) analytical ultracentrifugation combined with a Schlieren optical system (Mason and Huang, 1978 Weder and Zumbuehl, 1984) (2) the sedimentation field flow fractionation (SFFF) technique to separate heterogeneous dispersions (e.g., Kirkland et al., 1982). 

Another area of rapid growth for particle separation has been that of Field-Flow Fractionation (FFF) originally developed by Giddings (12,13>1 1 ) (see also papers in this symposium series). Like HDC, the separation in field-flow fractionation (FFF) results from the combination of force field interactions and the convected motion of the particles, rather than a partitioning between phases. In FFF the force field is applied externally while in HDC it results from internal, interactions. 

Field-Flow Fractionation Analysis of Macromolecules and Particles,... 

Cdlfen, H. and Antonietti, M.t Field-Flow Fractionation Techniques for Polymer and Colloid Analysis. VoL 150, pp. 67-187. 

FFF Field-flow fractionation GD-(MS) Glow-discharge (mass spectrometry)... 

Lee, H. Williams, S. K. R. Wahl, K. L. Valentine, N. B. Analysis of whole bacterial cells by flow field-flow fractionation and matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry. Anal. Chem. 2003, 75,2746-2752. 

Reschiglian, P. Zattoni, A. Cinque, L. Roda, B. Dal Piaz, F. Roda, A. Moon, M. H. Min, B. R. Hollow-fiber flow field-flow fractionation for whole bacteria analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Anal. Chem. 2004, 76,2103-2111. 

Schure, M.R. (1999). Limit of detection, dilution factors, and technique compatibility in multidimensional chromatography, capillary electrophoresis, and field-flow fractionation. Anal. Chem. 71, 1645-1657. 

There are many combinations of separations techniques and methods of coupling these techniques currently employed in MDLC systems. Giddings (1984) has discussed a number of the possible combinations of techniques that can be coupled to form two-dimensional systems in matrix form. This matrix includes column chromatography, field-flow fractionation (FFF), various types of electrophoresis experiments, and more. However, many of these matrix elements would be difficult if not impossible to reduce to practice. 

Venema, E., deLeeuw, P., Rraak, J.C., Poppe, H., Tijssen, R. (1997). Polymer characterization using online coupling of thermal field flow fractionation and hydrodynamic chromatography. J. Chromatogr. A 765(2), 135-144. 

In conclusion one can say that SEC is a very powerful method for polymer characterization, especially in combination with other composition sensitive or absolute calibration methods. A big advantage is also that the sample amount is fairly small, typically 10 mg. For more complex polymers, such as polyelectrolytes, enthalpic effects often become dominant and also for rather high molecular weight polymers chromatographic methods such as field-flow fraction (FFF) techniques might be more suitable. For fast routine measurements linear columns are often used. 

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