Solid-liquid equilibrium and dissolution thermodynamic properties of L-isoleucine in binary solvent mixtures

Thermodynamic properties, which play an important role in design and optimization of crystallization processes, are the essential data for the study of crystal nucleation and growth. In this study, the solubility of L-isoleucine were firstly determined by gravimetric method in three binary solvent mixtures including water + (ethanol, acetonitrile or DMSO) in the temperature range of 303.20 K to 338.05 K at atmospheric pressure. The effects of temperatures and solvent types on the dissolution process of L-isoleucine were investigated. It was found that the solubility of L-isoleucine increased dramatically with the increasing of the mole fraction of water in each binary solvent mixture and increased monotonically with the increasing of temperature. To extend the applicability of the solubility data, the experimental solubility data of L-isoleucine were fitted and analyzed using the modified Apelblat equation, the CNIBS/R-K model and the Jouyban-Acree model. Finally, based on the Van’t Hoff equation and the experimental solubility data, the apparent dissolution thermodynamic properties of L-isoleucine including apparent dissolution enthalpy, apparent dissolution entropy, and apparent Gibbs free energy change of dissolution process were calculated and discussed.