Rapid Separation of Micron-Sized Particles by Field-Flow Fractionation Using Earth's Gravitational Field

Influence of Operating Parameters On the Retention of Chromatographic Particles By Thermal Field-Flow Fractionation

We have investigated the retention behavior of chromatographic particles in thermal field-flow fractionation (FFF). Retention time is found to increase with increasing temperature drop across the channel thickness, as expected for species exhibiting a thermophoretic mobility. Experiments have been performed with a vertically oriented channel rather than by using the classical horizontal configuration as this leads to much more reproducible retention data. In acetonitrile, silica-based particles are more retained than octadecyl-bonded silica particles, which confirms our previous finding, by means of a different method, that the thermophoretic mobility of the latter is smaller than that of the former. Whatever the type of particles and the nature of the carrier liquid, the relative retention time is observed to decrease with increasing carrier flow rate. This indicates that a hydrodynamic lift force acts on particles to move them away from the accumulation wall, as is usually observed in all FFF experiments with micrometer-sized particles. However, upward and downward flow directions in the vertical channel lead to similar retention data, indicating that inertial lift forces have a minor influence on retention. In addition, the relative retention time steadily decreases with increasing sample concentration, suggesting that the hydrodynamic lift force increases significantly with sample concentration. Accordingly, we speculate that a new transport phenomenon, called shear-induced hydrodynamic diffusion, not previously accounted for in the modeling of retention in FFF, is controlling the migration of the particles in the FFF channel. Implications of the influence of this phenomenon in other FFF experiments are discussed.

Experimental design methodology applied to the study of channel dimensions on the elution of red blood cells in gravitational field flow fractionation

Field flow fractionation (FFF) separation techniques have gained considerable success with micron-sized species. Living red blood cells (RBCs) of any origin have emerged as ideal models for cell separation development. Their elution mode is now described as "Lift-Hyperlayer". Certain separator dimension parameters are known to play a key role in the separation and band spreading process. Systematic studies of channel dimensions effects on RBC retention, band spreading, peak capacity and on a novel parameter described as "Particle Selectivity" were set up by means of a two-level factorial experimental design. From experimental results and statistical calculations it is confirmed that channel thickness plays a major role in retention ratio, peak variance, peak capacity and particle selectivity. Channel breadth strongly influences plate height, with lower impact on peak capacity and particle selectivity. Retention ratio, peak variance and peak capacity observed results are modulated by second-order interactions between channel dimensions. Preliminary rules for channel configurations are therefore set up and depend on separation goals. It is shown that a very polydisperse population is best disentangled in a thin and narrow channel whatever its length. If a mixture of many different micron-sized species is considered (each of limited polydispersities); a thick and broad channel should be preferred, with length modulating peak capacity to disentangle this polymodal mixture.

Different elution modes and field programming in gravitational field-flow fractionation. 2. Experimental verification of the range of conditions for flow-rate and carrier liquid density programming

Gravitational field-flow fractionation utilises the Earth's gravitational field as an external force that causes the settlement of particles towards the channel accumulation wall. Hydrodynamic lift forces oppose this action by elevating of particles from the channel accumulation wall. Therefore there are several possibilities to modulate the resulting force field acting on particles in gravitational field-flow fractionation. Regarding the force field programming in gravitational field-flow fractionation, this work focused on two topics: changes of the difference between particle density and carrier liquid density in Brownian and focusing elution modes and influencing of lift forces achieved by changing the flow-rate in focusing elution mode. We have found and described the experimental conditions applicable to force field programming in the case of separations of silica gel particles by gravitational field-flow fractionation. It was shown that the effect of carrier liquid viscosity in the water-methanol system is implemented as an additional factor enhancing the desired effect of carrier liquid density. Some other forces influencing the retention behaviour of the model particles are discussed.

Micropreparation of hemopoietic stem cells from the mouse bone marrow suspension by gravitational field-flow fractionation

Gravitational field-flow fractionation is a relatively simple experimental technique. This method was used for the characterization of stem cells from mouse bone marrow. Because these cells are bigger than the other cells in bone marrow, it is possible to separate them from the mixture. The fractions collected after passing through the separation channel were characterized using a Coulter Counter and used for transplantation into irradiated mice.

Modification of glass channel walls for separation of biological particles by gravitational field-flow fractionation

In the gravitational field-flow fractionation of complex samples, various interaction and adsorption phenomena can occur in separation channels that influence fractionation and complicate the explanation of resulting fractograms. To overcome these problems, the glass surface was modified to create charge-free, non-adsorbing hydrophilic media for the mild treatment of hydrophilic biological particles. The modification was carried out in two steps: (1) by a simple lacquering of the glass surface with polystyrene diluted in toluene and (2) subsequent adsorption of a detergent layer on polystyrene. Essential suppression of ionic interactions between soluble low-molecular-mass compounds and the channel wall and decreased adsorption effects were demonstrated in separations of blood samples by gravitational field-flow fractionation.

Size- and density-dependent elution of normal and pathological red blood cells by gravitational field-flow fractionation

Elution of normal and pathological human red blood cells (RBCs) was performed by gravitational field-flow fractionation (GFFF). The reproducibility of the retention factor was lower than 10% and elution at high and low flow-rates confirmed the existence of "lifting forces". No direct correlation between size and retention was observed for normal RBCs in the absence of density information. Elution of pathological human RBCs, known to be modified in shape, density and rigidity, was performed. The elution parameters confirmed that the retention mechanism of RBCs is at least density dependent but that other factors can be involved, such as shape or deformity. Moreover, peak profile description parameters (standard deviation and asymmetry) can be qualitatively related to some biophysical parameters. Numerous elution characteristics can be linked to cell properties described in the literature and although GFFF appeared to have limited capabilities in terms of size analysis it appeared to be a versatile tool for studying cell biophysical characteristics.