Field-flow fractionation channel

Giddings, J. C. (1993). Micro-EPF Theoretical and practical aspects of reducing the dimensions of field-flow fractionation channels. J. Microcol. 5,497-503. 

Water at 20°C is pumped through a thin rectangular (ribbon-shaped) field-flow fractionation channel at a flowrate of 1.00 mL/ min. The channel dimensions (see Figure 4.2) are length L — 40.0 cm, breadth b = 2.00 cm, and thickness w = 254 fim. Calculate the average and maximum flow velocities, (u) and uraM, and the pressure difference Ap in atmospheres needed to drive the flow. 

The Flow Field-Flow Fractionation Channel as a Versatile Pressure Dialysis and Ultrafiltration Cell, J. C. Giddings, F. J. Yang, and M. N. Myers, Sep. Sci., 12, 499 (1977). 

Calculation of Flow Properties and End Effects in Field-Flow Fractionation Channels by a Conformal Mapping Procedure, P. S. Williams, S. B. Giddings, and J. C. Giddings, Anal. Chem., 58, 2397 (1986). 

Wahlund, K.-G. Giddings, J.C. Properties of an asymmetrical flow field-flow fractionation channel having one permeable wall. Anal. Chem. 1987, 59, 1332-1339. 

Wahlund, K.G. Litzen, A. Application of an asymmetric 14. flow field-flow fractionation channel to the separation and characterization of proteins, plasmids, plasmid fragments, polysaccharides, and unicellular algae. J. Chromatogr. 15. 1989, 461, 73. 

A. Litzen and K. G. Wahlund. Zone broadening and dilution in rectangular and trapezoidal asymmetrical flow field-flow fractionation channels. Anal. Chem. 63 1001 (1991). 

Figure 1. Schematic of an FFF channel with the separation mechanism for normal FFF shown in detail. Reprinted from [7] Beckett, R. and Hart, B. T. Use of field flow fractionation techniques to characterize aquatic particles, colloids and macromolecules . In Environmental Particles. Vol. 2, IUPAC Series on Analytical and Physical Chemistry of Environmental Systems. Series eds. Buffle, J. and van Leeuwen, H. P., pp. 165-205. Copyright 1993 IUPAC. Reproduced with permission...

Field flow fractionation (FFF), as a gentle size fractionation coupled to ICP-MS, offers the capability to determine trace metals bound to various size fractions of colloidial and particulate materials.112 On line coupling of FFF with ICP-MS was first proposed by Beckett in 1991 -113 Separation is achieved by the balance between the field force and macromolecular diffusion in the FFF channel. Depending on the field force used, FFF is classified into different techniques such as sedimentation, gravitational, electrical, thermal and flow FFF.112... 

FIG. 2.1 Sedimentation field flow fractionation (SdFFF) (a) an illustration of the concentration profile and elutant velocity profile in an FFF chamber and (b) a schematic representation of an SdFFF apparatus and of the separation of particles in the flow channel. A typical fractionation obtained through SdFFF using a polydispersed suspension of polystyrene latex spheres is also shown. (Adapted from Giddings 1991.)... 

Most data about the Ludwig-Soret effect of polymers in solution have been obtained from thermal field-flow fractionation (TFFF), developed by Giddings and coworkers [17,18]. TFFF is one member of the family of field-flow fractionation techniques, which are all characterized by a laminar flow of the polymer solution or colloidal suspension within a relatively narrow channel. An external field, which may be gravitation, cross-flow, or temperature as in TFFF, is applied... 

Figure 13.6. Separation principle of field-flow fractionation (FFF) is based on physical interactions of particles within an applied field and subsequent field-induced migration to the FFF channel wall ( accumulation wall ). Molecules, depending on their size and diffusion coefficient, are distributed over different velocity lines of axial flow, and they separate accordingly. Larger particles possess less diffusional motion and higher interaction with the applied field hence, they will be caught up in slower-moving streams near the channel wall and elute later than smaller particles.

Lyven, B., Hassellov, M., Haraldsson, C. and Turner, D.R. (1997) Optimisation of on-channel preconcentration in flow field-flow fractionation for the determination of size distributions of low molecular weight colloidal material in natural waters. Anal. Chim.Acta, 357, 187-196. 

In FFF systems, the separation along the flow axis is caused by the perpendicular field, whose crucial role is recognized by the word "field" 1n field-flow fractionation. The applied field Interacts with entrained particles, forcing them to accumulate at one wall (the accumulation wall) of the channel. Since the flow velocity near any wall is reduced by frictional drag, the downstream displacement of the particles 1s retarded. Retardation (or retention) is greatest for those particles forced most closely to the wall. Consequently, particles are separated according to the different forces exerted on them by the applied field. These forces normally depend on particle size, leading to a size-based separation. 

Flow in a thin rectangular channel (Figure 4.2), such as that used in field-flow fractionation, can be treated in a manner similar to that used for cylindrical capillary tubes. If the drag at the edges of the channel is neglected (infinite parallel plate model), then the force balance expression (corresponding to Eq. 4.5 for capillary tubes) becomes... 

In field-flow fractionation, a component undergoing flow transport through a thin channel is forced sideways against a wall by an applied field or gradient. The component is confined to a narrow region adjacent to the wall, by a combination of the wall s surface, which it cannot pass, and the driving force, which prevents its escape toward the center of the channel. The component molecules or particles soon establish a thin steady-state distribution in which outward diffusion balances the steady inward drift due to the field. The structure and dimensions of this layer determine its behavior in the separation process. 

Displacement and Dispersion of Particles of Finite Size in Flow Channels with Lateral Forces. Field-Flow Fractionation and Hydrodynamic Chromatography, J. C. Giddings, Sep. Sci. Technol., 13, 241 (1978). 

Capillary Liquid Chromatography in Field-Flow Fractionation-type Channels, J. C. Giddings, J. P. Chang, M. N. Myers, J. M. Davis, and K. D. Caldwell, J. Chromatogr., 225, 359 (1983). 

Separation in Thin Channels Field-Flow Fractionation and Beyond, J. C. Giddings, in J. D. Navratil and C. J. King, Eds., Chemical Separations, Vol. 1, Litarvan, Denver, 1986, pp. 3-20. 

Fig. 26. Schematic design of field flow fractionation (FFF) analysis. A sample is transported along the flow channels by a carrier stream after injection and focusing into the injector zone. Depending on the type and strength of the perpendicular field, a separation of molecules or particles takes place the field drives the sample components towards the so-called accumulation wall. Diffusive forces counteract this field resulting in discrete layers of analyte components while the parabolic flow profile in the flow channels elutes the various analyte components according to their mean distance from the accumulation wall. This is called normal mode . Particles larger than approximately 1 pm elute in inverse order hydrodynamic lift forces induce steric effects the larger particles cannot get sufficiently close to the accumulation wall and, therefore, elute quicker than smaller ones this is called steric mode . In asymmetrical-flow FFF, the accumulation wall is a mechanically supported frit or filter which lets the solvent pass the carrier stream separates asymmetrically into the eluting flow and the permeate flow which creates the (asymmetrical) flow field...

In two papers, Palkar and Schure studied the mechanism of electrical field-flow fractionation in detail [269,270]. An electrical circuit of the channel was... 

In thermal field flow fractionation (TFFF), a temperature gradient is applied. The primary potential advantage of this technique is that it can be used to size particles in the range 0.01 pm to 0.001 pm, an order of magnitude smaller than SFFF. Fffractionation market a TFFF polymer fractionator channel module with 286/16 MHz IBM compatible PC, super VGA color monitor workstation to include data acquisition software, hardware and data analysis software. A linear UV detector and single channel high performance pump are optional. 

Field-flow fractionation (FFF) technology is applicable to the characterization and separation of particulate species and macromolecules. Separations in FFF take place in an open flow channel over which a field is applied perpendicular to the flow. Among the various FFF subtechniques, depending on the kind of the applied external fields, sedimentation FFF (SdFFF) is the most versatile and accurate, as it is based on simple physical phenomena that can be accurately described mathematically. SdFFF, which uses a centrifugal grav-... 

Field-flow fractionation is a highly promising tool for the characterization of colloidal materials. It is a dynamic separation technique based on differential elution of the sample constituents by a laminar flow in a flat, ribbonlike channel according to their sensitivity to an external held applied in the perpendicular direction to that of the flow. 

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