Solubility and thermodynamic analysis of amlodipine besylate in mixtures of propylene glycol and 1-propanol from 293.2 to 323.2 K

The solubility characteristics of amlodipine besylate (ADB) in various propylene glycol and 1-propanol mixtures were quantitatively determined using a spectrophotometric approach, post equilibration via the established shake-flask technique. This solubility quantification was extended across a spectrum of five distinct temperatures, ranging from 293.2 K to 313.2 K, in conjunction with eleven discrete mass fractions. It was observed that the solubility of ADB exhibited an enhancement concomitant with an increase in the propylene glycol mass fraction, culminating in a maximal solubility value at 313.2 K for a propylene glycol mass fraction of 0.8. The solubility data of ADB was subjected to correlation analysis using a variety of linear cosolvency models, yielding mean percentage deviations spanning from 1.0 % to 24.8 %. In the realm of thermodynamics, the apparent parameters, namely enthalpy, entropy, and Gibbs free energy, pertinent to the dissolution processes of ADB were computed. The derived enthalpy-entropy relationship for ADB demonstrated a non-linear behavior. Specifically, the plot of enthalpy against Gibbs energy revealed positive slopes in the ranges of w₁=0.0 to w₁=0.1, w₁=0.2 to w₁=0.3, w₁=0.4 to w₁=0.5, w₁=0.6 to w₁=0.7, and w₁=0.8 to w₁=1.0 in these mixtures, but transitioning to negative slopes between w₁=0.1 and w₁=0.2, w₁=0.3 to w₁=0.4, w₁=0.5 to w₁=0.6, and w₁=0.7 to w₁=0.8.