Athanasia Koliadima

Potential barrier field-flow fractionation for the separation and characterization of colloidal particles

SummaryThe reversibility of adsorption of colloidal particles on the channel wall in Sedimentation Field-Flow Fractionation (SFFF), which is based on the variation of the ionic strength of the carrier solution, suggests a new method, for the separation and characterization of colloidal materials. This new method has been called “Potential Barrier Field Flow Fractionation” (PBFFF).

Size Analysis of Barley Starch Granules by Sedimentation/Steric Field Flow Fractionation

In the present work the relatively new technique of sedimentation/steric field-flow fractionation (Sd/StFFF) was used for the size analysis of the large, medium and small starch granules of barley grain. The experimental parameters varied were the time from the preparation of the starch sample dispersion - in order to study the disintegration or the aggregation of the starch granules - and the concentration of the sample -in order to study the sample overloading effect on the measured size of the starch granules. A bimodal or trimodal size distribution curve, depending on the experimental conditions used, was found by Sd/StFFF, and the number and weight average diameters of the starch granules were calculated. Finally, the experimental results are compared with those obtained by scanning electron microscopy and light scattering, and useful conclusions concerning the destruction or the aggregation of the starch granules, as well as the sample overloading effect on the granules size, measured by Sd/StFFF, are extracted.

Concentration and characterization of dilute colloidal samples by potential-barrier field-flow fractionation

SummaryPotential-barrier field-flow fractionation, which is a combination of potential-barrier chromatography and sedimentation field-flow fractionation, is shown to be a convenient and accurate method for the concentration and analysis (separation and characterization) ofdilute colloidal samples. Two sizes (0.158 and 0.271 μm) of haematite (α-Fe2O3) monodisperse colloidal samples diluted in volumes of up to 20 cm3 are used as model colloids. The particle diameters found by the present concentration procedure under various experimental conditions are in good agreement with those determined by conventional sedimentation field-flow fractionation, in which a small concentrated sample volume was injected directly into the column.

Sedimentation Field-Flow Fractionation: A New Methodology for the Concentration and Particle Size Analysis of Dilute Polydisperse Colloidal Samples

Abstract It is shown that the on-channel concentration procedure for the analysis of dilute monodisperse colloidal samples in sedimentation field-flow fractionation, as established in a previous work(1), provides an accurate methodology for the concentraion and particle size analysis of dilute polydisperse colloidal samples. In order to test the methodology experiments are described using polyvinyl chloride (PVC) latex beads in the diameter range 0.173–0.334 μm. A series of fractograms were run in which the amount of the PVC sample was held constant while the volume in which it was contained was varied over a 20,000-fold range. The weight average particle diameters and the particle size distribution curves (histograms or cumulative distribution curves), determined by the on-channel concentration procedure at various experimental conditions, are in excellent agreement with those obtained under normal experimental conditions, in which a small concentrated volume of the same sample is injected directly into ...

Conversions of carbon monoxide oxidation over Pt−Rh alloy catalysts calculated by a new gas chromatographic technique

SummaryCatalytic fractional conversions of carbon monoxide to carbon dioxide over Pt−Rh alloy catalysts in the presence of excess oxygen, under steady-state or non steady-state conditions, as well as corresponding rate constants for the CO oxidation reaction were measured by using the reversed-flow gas chromatographic technique. From the variation of the conversions with temperature, maximum values of conversions were found, which depend on the catalysts nature (Pt content), while from the variation of the rate constants with temperature, activation energies for the CO oxidation reaction were determined, which also depend on the catalyst Pt content. The results suggest a synergism between Pt and Rh in the Pt−Rh bimetallic catalysts in accordance with previous works, showing that reversed-flow gas chromatography can be used with simplicity and accuracy for the kinetic study of the CO oxidation reaction, which is of technological importance for the control of air pollution.

Kinetic study of cell proliferation of Saccharomyces cerevisiae strains by sedimentation/steric field flow fractionation in situ.

The technique of Sedimentation/Steric Field Flow Fractionation (Sd/StFFF) is applied to the kinetic study of cells proliferation of Saccharomyces cerevisiae strains. The experimental parameter varied is the time from the preparation of the yeast sample dispersion in the culture medium. The determination of the size and mass distributions of the yeast cells is combined with the growth of the yeast cells and their life cycle. The experimental results are compared with those obtained by scanning electron microscopy (SEM) and those found in the literature. Useful conclusions concerning the budding and the fission of these yeast cells were extracted.

Estimation of solubility and interaction parameters in binary liquid mixtures by reversed-flow gas chroamtography

SummaryA new method, called reversed-flow gas chromatography, is presented for the measurement of the gaseous equilibrium concentrations of all the components under study, both in the pure state and in binary liquid mixtures. From the equilibrium concentrations, activities, activity coefficients and volume fraction activity coefficients were determined. Using various empirical equations relating activity with the molecular interactions between the components of a binary liquid mixture, the solubility parameters of ethanol, 1-propanol, acetone and methylethylketone in water were calculated. The total interaction parameters and the partial contributions of the dispersion, orientation and “residue” forces on the van der Waals attraction between the organic compounds and water were also computed. The variation of the interaction parameters with the composition of organic component in the binary mixture was investigated. The successful application of reversed-flow gas chromatography to the estimation of polymer solubility parameters is also reported. Finally, the solubility parameters found by the present method are compared with those determined by other techniques or calculated theoretically.

New separation methodologies for the distinction of the growth phases of Saccharomyces cerevisiae cell cycle

In the present work two separation techniques, namely the gravitational field-flow fractionation (GrFFF) and the reversed-flow gas chromatography (RFGC), are proposed for the distinction of the growth phases of Saccharomyces cerevisiae (AXAZ-1) yeast cycle at different temperatures (30 degrees C, 25 degrees C, 20 degrees C, and 15 degrees C) and pH (2.0, 3.0, 4.0 and 5.0) values. During the fermentation processes, differences observed in the peak profiles, obtained by GrFFF, can be related with the unlike cell growth. The distinction of the phases of AXAZ-1 cell cycle with the GrFFF, was also confirmed with the RFGC technique, which presented similar fermentation time periods for the alcoholic fermentation phases. Simultaneously, the reaction rate constant for each phase of the fermentation process and the activation energies were determined with the aid of the RFGC technique. Finally, the application of both the GrFFF and the RFGC techniques, in combination with high-performance liquid chromatography, allowed us to find the ideal experimental conditions (temperature and pH) for the alcoholic fermentation by AXAZ-1. The results indicate that S. cerevisiae cells performed better at 30 degrees C, whereas at lower temperatures decreases in the fermentation rate and in the number of viable cells were observed. Moreover, the pH of the medium (pH 5.0) resulted in higher fermentation rates and ethanol productivities.

STUDY OF THE INFLUENCE OF IONIC STRENGTH AND pH OF THE SUSPENDING MEDIUM ON THE SIZE OF WHEAT STARCH GRANULES, MEASURED BY SEDIMENTATION/STERIC FIELD-FLOW FRACTIONATION

The sedimentation/steric field-flow fractionation (Sd/StFFF) technique has been approved as a simple and accurate method for the size separation and characterization of starch granules. In the present work, we further investigate this application by studying the influence of the ionic strength and the pH of the suspending medium on the size of the wheat starch granules measured by Sd/StFFF. A bimodal size distribution curve was found by Sd/StFFF for the starch granules, in accordance with the results obtained by scanning electron microscopy (SEM). The number and weight average diameters for the large (A-type) and small (B-type) starch granules are independent of the presence of the indifferent electrolyte KNO3 in the suspending medium, indicating that disintegration or aggregation phenomena of the starch particles are absent. The later was also verified by SEM. The fact that the suspension pH does not influence the number and weight average diameters of the starch granules is discussed, in relation to the zeta potentials of the particles, which were measured by a microelectrophoresis apparatus.

Dependence of Adsorption Rates with Lateral Interactions on Local Surface Coverage of Heterogeneous Surfaces

SummaryAs local adsorption isothermθf changes with time, it induces a changing with it of both, the net experimental adsorption rate∂θf/∂f with lateral molecular interaction, as well as the rate constants for adsorption (ko) and desorption (kd). All these changes are experimentally measured by applying the reversed-flow gas chromatographic method, and a relatively simple equation.These calculations have been applied to the adsorption of dimethyl sulfide on pieces of Penteli marble at 373 K and to the adsorption of heptane on γ-alumina at 383 K.