J. Janča

Concentration effects in gel permeation chromatography : I. Polymer solution properties

Abstract Equations have been derived that give a quantitative description of the processes that occur in a chromatographic column, leading to a concentration dependence of the elution volume in the gel permeation chromatography of polymers. The concentration dependence was studied experimentally on rigid porous glass, that is, under conditions when the size of the accessible pores is not influenced by a change in the thermodynamic properties of the solvent. The experimental data were correlated with the relationships obtained in the investigation.

Concentration effects in gel permeation chromatography : IV. Contribution of viscosity phenomena and macromolecular expansion

Abstract The changes in elution volumes with the changes in the concentration of an injected polymer solution are caused by several contributing effects. Under model conditions, it is possible to assume only the effect of a viscosity gradient in a zone moving along the column and the effect of the concentration dependence of the hydrodynamic volume of a macromolecular coil. The non-Gaussian shape of the zone and the dependence of the width of the elution curve on concentration are factors that complicate the theoretical treatment of concentration effects. The described physico-chemical model allows to evaluate the ratio of mentioned two contributions in the concentration dependence of elution volumes. According to this model, the contribution of the concentration dependence of the hydrodynamic volume does not exceed about 20% of the total change in elution volume with the varying concentration under real experimental conditions. The efficiency of the columns used and the total injected volume of the polymer solution affect this ratio only negligibly. It is obvious from a comparison with earlier results that these conclusions are not fundamentally changed even by the revised model of the concentration dependence of the swelling factor.

Sedimentation-Flotation Focusing Field-Flow Fractionation in Channels with Modulated Cross-Sectional Permeability. I. Theoretical Analysis

Abstract A new-shaped cross-section of a channel with modulated permeability used in Sedimentation-Flotation Focusing Field-Flow Fractionation is proposed. The shape of the resulting velocity profile inside the channel is described as a function of the geometric channel characteristics. Basic separation parameters such as retention, efficiency and the related resolution are discussed. The principle of a channel with modulated permeability can also be applied to other subtechniques of Field-Flow Fractionation.

Sedimentation-Flotation Focusing Field-Flow Fractionation in Channels with Modulated Cross-Sectional Permeability. II. Experimental Implementation

Abstract The first experimental separation of the model particles according to their differences in densities by a new Sedimentation-Flotation Focusing Field-Flow Fractionation (SFFFFF) method is described. The SFFFFF was accomplished in a simple fractionation channel by using a density gradient medium and applying the natural gravitational field of 1 G. Although the experimental results are of the preliminary character, they proved decisively the real potential of the SFFFFF.

Concentration effects in gel permeation chromatography

Abstract Viscosity phenomena were studied in columns with considerably diverse geometrical parameters. It was found that these phenomena, characterized quantitatively by statistical parameters and qualitatively by comparison of the shapes and changes in chromatograms, are identical for different geometrical arrangements. Hydrodynamic transport processes, which give rise to viscosity phenomena in chromatography of polymers, are thus general. The significance of the results ranges beyond the area of gel permeation chromatography of polymers since hydrodynamic transport processes are found every time polymer solutions pass through porous material, e.g. , in technological separation processes and the transport of macromolecules in biological media.

Optimization of Field-Flow Fraction-Ation with Respect to Relaxation and Use of Stop-Flow Technique at Constant Field Operation

Abstract The relaxation phenomena developing after the injection of the sample into the channel during Field-Flow Fractionation were analyzed theoretically. Relaxation times, necessary to stop the flow immediately after the injection, were calculated on the basis of various models describing the relaxation processes. A stop-flow time long enough so that the deviation from the equilibrium would not influence the retention within the limits of experimental errors and so that the maximum efficiency would be reached was required. Sedimentation Field-Flow Fractionation was used to verify the theoretical analysis. The diffusion coefficient of latex used for the study is small and thus the long relaxation times allow to reach sufficient precision of the measurement. The experiments performed at different flow rates and using different ways of sampling proved a good agreement between the experimental relaxation times and the values calculated theoretically. The stop-flow technique was proved both theoretically an...

Concentration effects in gel permeation chromatography : V. Differential elution and viscosity phenomena

Abstract The viscosity phenomena that take place in the interstitial volume of a chromatographic column and are connected with changes in the concentration and specific viscosity of an injected polymer solution have been studied. These phenomena were also studied under conditions of differential elution when, instead of a pure solvent, solutions of the same polymer at concentrations both higher and lower than those of the injected sample were used as the mobile phase. Linear relationships were found between the elution volume and specific viscosity and between the efficiency and specific viscosity. It was also ascertained that these dependences hold under conditions of differential elution; accordingly, the absolute viscosity of the mobile phase is of minor importance for the phenomena investigated.

Progress in field-flow fractionation: theory, methodology and applications

Abstract The history of Field-Flow Fractionation (FFF) began in 1966 when Giddings (1) described a new separation concept based on a coupling of solute concentration and fluid flow nonuniformities inside a narrow channel, which cause the differential migration of the solute species and thus the separation. Physical or chemical lateral field acting across the channel composed usually of two planparallel walls (e.g., temperature gradient, electrical, magnetic or gravitational forces, chemical potential gradient etc.), interacts with molecules or particles of the solute and compresses them to one of the channel walls in the direction of x-axis, perpendicular to this wall. This concentration gradient induces a diffusion flux in the reverse direction. After certain time a steady state is reached and the distribution of the solute across the channel can be characterized by a mean layer thickness l.

Concentration Effects in Size Exclusion Chromatography Under Equilibrium Stationary Conditions

Abstract In size exclusion chromatography the elution volume increases with increasing concentration of injected polymer solutions. Several particular processes contribute to this concentration effect. Under model equilibrium stationary conditions, where the phases remain immobile, it is possible to eliminate dynamic phenomena connected with the higher viscosity of polymer solution in the chromatographic zone. The only factors operative here are the effect of changes in the effective size of macromolecules in solution with a change in concentration and the effect of the varying accessible pore volume with varying concentration. The ratio of these two contributions has been investigated both theoretically and experimentally. Theoretical calculations indicated that with both phenomena operating simultaneously, the elution volumes may increase or decrease with increasing concentration according to the given experimental conditions, as a result of the coupled influence of molecular parameters of the samples u...

Field-flow fractionation in biopolymer analysis

Abstract Field-flow fractionation is a new separation method convenient for the analysis of biopolymers within a wide range of molecular weights, and of particles of biological origin. It is similar to chromatography, but in principle exhibits many advantages over alternative separation methods.