Jari Tiihonen

Complex stability of sugars and sugar alcohols with NA + , CA 2+ , and LA 3+ in chromatographic separations using poly(styrene- CO -divinylbenzene) resins and aqueous organic eluents

The complex formation between metal ions and carbohydrates in solvent mixtures has been studied by chromatographic measurements. The effect of noncomplexing partition was decreased by attaching the active groups only on the shell of the stationary phase particles. Poly(styrene- co -divinylbenzene) resin beads were surface-sulfonated for that purpose. Thus the inner part of the sulfonated bead remained inactive and nonswellable. The counter-ions examined were Na + , Ca 2+ , and La 3+ , and the organic cosolvents were ethanol and acetonitrile. The stability constants of the very weakly complexing D -glucose, D -xylose, and L -rhamnose, the weakly complexing D -fructose and L -arabinose, and the strongly complexing xylitol and D -sorbitol were determined. The increasing organic cosolvent content increased the retention times, which is explained by the increased complex stability between the complexing solute and the counter-ion. The effect was greatest for the complex-forming sugars in the Ca 2+ form and for the sugar alcohols in the La 3+ form. The organic cosolvent had only a minor effect on the weakly complexing components, whereas the complex stability of the strongly complexing xylitol and sorbitol in 50 wt% ethanol solution in the La 3+ resin was more than five times higher compared to the stability measured in pure water.

Co-eluent effect in partition chromatography. Rhamnose-xylose separation with strong and weak cation-exchangers in aqueous ethanol.

The effect of ethanol in aqueous eluent on the chromatographic separation was studied at 298 K. Two sugars, L-rhamnose and D-xylose, were separated by using strong and weak cation-exchangers as a stationary phase. The ionic form of the resins was Na+ or Ca2+. The separations were carried out with sugar feed concentrations up to 35 wt% and with both low (about 1%) and high (about 10%) feed volume to bed volume ratios. The separation of the sugars was improved by adding ethanol into the eluent. The separation was also significantly enhanced when the weak cation-exchangers with the greatest affinity for water were used instead of strong cation-exchangers as a separation medium for the sugars having different hydrophilicities. The experimental data were successfully explained with a rate-based column model, which accounted for the volume changes of the stationary phase. A thermodynamic sorption model was utilized in column calculations.

Modelling the sorption of water–ethanol mixtures in cross-linked ionic and neutral polymers

Abstract Water–ethanol sorption in strong sulfonated polystyrene cation-exchangers, in weak acrylic cation-exchangers and in neutral cross-linked dextran gels as well as their elastic properties have been measured. The effect of polymer matrix and cross-link density have been studied. The ionic resins were mainly in the Na+ form. The data have been analyzed by means of thermodynamic mixing models based on the Flory–Huggins equation, quasi-chemical UNIQUAC and non-random factor equations. The elasticity of the polymer networks was incorporated in the models as an additional free energy term and two elastic models derived for non-ideal networks were tested. The quasi-chemical approach using the non-random factors proved to be the best choice for calculating the mixing effects in the sorption equilibrium model. Experimental shear modulus data showed that the elastic properties of the ionic resins can be described adequately only by the model which takes into account the limited extensibility of the polymer chains. The elastic parameters estimated from the modulus data were used in the equilibrium model and a semi-quantitative correlation with the sorption data was obtained. Both the experimental data and modelling results indicated that the studied materials respond distinctly differently to the external solvent composition and have characteristic sorption properties. The polymer matrix type and ionic group density had clear effects on the phase transitions from gel-like to glassy polymer in different aqueous ethanol mixtures. Furthermore, the hydrophilicity and the water selectivity depended strongly on the polymer type. The acrylic acid resin was the most hydrophilic and had also the highest water selectivity. The water selectivity of the sulfonated PS–DVB resins and the dextran gels was approximately equal.