Thermodynamic study of three anhydrous polymorphs of d-mannitol in different binary solvent mixtures from T = (258.15 to 278.15) K

Abstract

In this work, the solubility of three pure anhydrous polymorphs of d-mannitol (α form, β form, and δ form) in binary solvent mixtures, including (methanol-water) and (ethanol-water), was determined by a HPLC method with the temperature ranging from (258.15 to 278.15) K at atmospheric pressure (0.1 MPa). The experimental results indicate that the solubility of the three polymorphs increases with temperature and decreases with the rise of the organic component (methanol and ethanol) ratio in the binary solvents. Moreover, the solubility of three d-mannitol polymorphs ranks as (δ form) > (α form) > (β form) under the same condition. Additionally, the modified Apelblat model, Buchowski-Ksiazaczak λh model, Ma model and NRTL model are used to correlate the solubility data in binary solvents. Furthermore, the thermodynamic properties of mixing process of d-mannitol polymorphs, including the Gibbs energy change, entropy and enthalpy, were also calculated and discussed.