Thermodynamics of non-stoichiometric pharmaceutical hydrates

Different physical and mathematical models of non-stoichiometric hydrates derived form previous work in inorganic hydrates are reviewed. A theoretical link between the order of water molecules in the hydrate and the shape of the isotherm is outlined. The comparison of the models with sorption isotherms and structural data of well-known cases from the literature and one in-house case shows that the model can fit many experimental situations and is in good agreement with qualitative assessments of the order in the hydrates.