Solubility analysis of buspirone hydrochloride polymorphs: Measurements and prediction

In this paper, the solubility of two polymorphs of buspirone hydrochloride (BUS-HCl) in isopropanol, water and mixture of these two solvents has been investigated. The solubility of BUS-HCl Form 2 in water and isopropanol is higher than BUS-HCl Form 1. According to thermodynamic properties and Burger and Ramberger polymorphic rules (Bernstein, 2002), BUS-HCl Forms 1 and 2 are enantiotropes (Sheikhzadeh et al., 2007). Using the solubility data, transformation analysis has been done and the results confirm these two polymorphs are enantiotropes and Form 1 converts to Form 2 at 95 °C. The UNIQUAC binary adjustable parameters have been found and based on these parameters, the solubility of these molecules has been predicted and compared with the experimental solubility. The solubility prediction has been performed by using different UNIFAC equations for binary and ternary systems. The UNIQUAC and original UNIFAC showed better prediction capability. Different general solubility equations (GSE) have been used for estimation of solubility which works based on partial charge, hydrogen bond factors and partition coefficients.