Colloid characterization by sedimentation field-flow fractionation

The advantages of hydrodynamic relaxation in field-flow fractionation, in which an injected sample is driven rapidly toward its equilibrium distribution by flow, are described relative to conventional field-driven relaxation. A new concept for achieving hydrodynamic relaxation, based on the use of permeable wall elements (or frit elements) embedded in the channel walls, is introduced. Here an auxiliary substream of carrier fluid, permeating uniformly into the FFF channel near the inlet, drives the sample, entrained in its own substream, close to its equilibrium configuration. Such frit elements can also be used to enrich the sample at the outlet. Equations are derived and plots are provided for the position of the splitting plane dividing the two substreams; this position defines the strength of the hydrodynamic relaxation. Variations in shear through these frit-modified end regions are also formulated and plotted. The effects of frit elements on band broadening are discussed. It is concluded that permeable wall elements in many configurations may be broadly applicable to FFF and related methods for improved sample introduction, increased separation speed, reduced risk of sample adhesion to the wall, improved flow stability, and sample enrichment.

Section: Discussionmentioning

confidence: 99%

Hydrodynamic relaxation and sample concentration in field-flow fractionation using permeable wall elements

Giddings¹

1990

“…The triangular area, defined by the dashed lines on the center spacer (Mylar film b), acts as a splitter. In addition, the standard sedimentation FFF system was modified to incorporate two inlets into the system for the two entering substreams of split inlet flow, A similar modification has been described elsewhere (8),…”

Section: Methodsmentioning

confidence: 99%

“…This broadened band causes an incremental increase in the measured plate height. The incremental plate height due to relaxation is related to h0 by (1) Hr = 17V/140L (8) With the substitution of h0 from eq 5, this becomes 39.3idV(d)2 r_ d*G2Ap2L (9) which shows that HT decreases rapidly with increasing particle diameter.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamic relaxation using stopless flow injection in split inlet sedimentation field-flow fractionation

Lee¹,

Myers²,

Giddings³

1989

In this paper relaxation effects in both the normal and steric operating modes of sedimentation field-flow fractionation are examined by using three different injection procedures: stop flow, stopless flow, and a new stopless flow procedure employing an inlet splitter. In the usual operation of field-flow fractionation (FFF), a stop procedure is used in which the channel flow is halted for an adequate period of time after injection for sample relaxation (in which the sample particles approach equillibrium near one wall) before the resumption of channel flow. If the channel flow is not stopped (stopless flow procedure), the elution profile is shifted and distorted due to the downstream migration of the particles during the relaxation process. To avoid peak distortion while retaining the advantages of the stopless flow procedure, a physical splitter at the channel inlet divides the entering flow stream into two substreams; sample is injected into only one of these. In this way a rapid (although not complete) hydrodynamic relaxation is realized. This stopless split flow injection procedure is compared to ordinary stop and stopless flow procedures using both submicrometer (normal FFF) and supramicrometer (steric FFF) polystyrene latex particles. It is found that much of the distortion normally accompanying stopless flow injection is eliminated by this new procedure. However, further optimization is needed to match the high resolution of the stop flow method.

“…The operation of the split-outlet end of the sedimentation FFF channel used for one sample concentration procedure is illustrated in Figure 1. The modifications that must be made in a normal sedimentation FFF apparatus in order to implement split-outlet enrichment are described in a recent paper (13). We note that this system does not utilize a physical splitter extending back from the outlet end, but simply takes advantage of the splitting capabilities of two well aligned outlet ports (13).…”

Section: Methodsmentioning

confidence: 99%

“…The modifications that must be made in a normal sedimentation FFF apparatus in order to implement split-outlet enrichment are described in a recent paper (13). We note that this system does not utilize a physical splitter extending back from the outlet end, but simply takes advantage of the splitting capabilities of two well aligned outlet ports (13). The dimensions of the split-outlet channel (used only for the split-outlet experiments) are tip-to-tip length L = 90.5 cm, thickness w = 0.0254 cm, breadth b = 2.00 cm, distance from rotor to channel r0 = 15.3 cm, and void volume V°= 4.92 mL.…”

Section: Methodsmentioning

confidence: 99%

Separation and characterization of colloidal materials of variable particle size and composition by coupled column sedimentation field-flow fractionation

Jones¹,

Giddings²

1989

Coupled column field-flow fractionation (FFF), In which a narrow fraction collected from one run is reinjected for a second FFF run under different conditions, Is shown to be a multidimensional technique analogous to coupled column chromatography. By using different carrier densities In successive sedimentation FFF stages, this approach Is theoretically capable of unraveling both the size and density characteristics of the components of complex colloids. This concept Is tested here by preparing simple binary mixtures of polystyrene (PS) and poly(vinyl chloride) (PVC) latex particles; coupled column FFF is then used to recover size and density Information on the PS latex despite the presence of the PVC "contaminant". The problem of transferring enough of a sample fraction from the first stage to the second to provide an adequate detector signal Is approached by three concentration methods: split-outlet concentration, on-channel concentration, and centrifugation. All work reasonably well, but Improvements In some of these techniques would greatly simplify the practical usage of coupled column FFF.