In this paper we investigate the equilibrium uptake of neutral, basic, and acidic amino acids by strongly basic anion-exchange resins in the hydroxyl form. Because homogeneous and heterogeneous equilibria take place, both solution and ion-exchange equilibria were studied. A model that takes account of the variation of the separation factor with the ionic fraction in solution was used to correlate the experimental data.10.

This work is a study of the behavior of amino acids on columns of strong anion-exchange resins in displacement chromatography. A new technology allowing the minimization of pollutant reagents was applied. It consists of using dissolved carbon dioxide in water as a displacer. The emphasis was also placed on the use of unbuffered solutions of amino acids in water. A mathematical model for the displacement process was constructed. Ion-exchange equilibrium relations based on variable selectivity coefficients and dissociation reactions of amino acids were incorporated in the model. It is shown that, in the case of negligible hydrodynamic and kinetic resistances, pure and concentrated products could be obtained.

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This investigation examines and compares the water sorption isotherms and the thermodynamic properties of two pharmaceutical preparations (Hypril and Azix) intended to be manufactured with the same process plant and equipment. The moisture equilibrium isotherms were determined at 50, 60 and 70 °C using a gravimetric technique. Five isotherm models were explored for their fitting to the experimental data. Azix showed sigmoid type II isotherms while Hypril showed type III isotherms according to the BET classification. All investigated models fitted well the water sorption isotherms of Hypril. By contrast, only GAB and Adam and Shove equations gave appropriate fit to the experimental data of Azix. For both formulations, the isosteric heat and the differential entropy decreased sharply with the increase of equilibrium moisture content to minimum values and thereafter remain constant. In the case of Azix, the integral enthalpy decreased with equilibrium moisture content while the integral entropy increased until reaching a constant value. Contrariwise, Hypril showed decreasing of the integral enthalpy and entropy with the equilibrium moisture content. Keywords: sorption isotherm, enthalpy, entropy, spreading pressure, pharmaceutical formulations

In this paper we investigate displacement chromatography of amino acids on columns of strong anionic resins in the hydroxyl form. The displacer used here is carbon dioxide dissolved in water, but the theory is also valid to other types of displacers. A theoretical study of the effect of both dissociation equilibria in solution and ion-exchange equilibria is presented. It is shown that the separation quality depends not only on the selectivity coefficient but also on a term relative to homogeneous equilibria in the liquid phase. This factor is related to the ratio of the second amino acid deprotonation constants.