Experimental and thermodynamic analyses of supercritical CO2-Solubility of minoxidil as an antihypertensive drug

Abstract

A major challenge in the production of micro/nano-sized drug particulates is to understand the solubility behavior of the drug in a supercritical fluid (SCF). In the present study, solubility of Minoxidil, an antihypertensive drug, in SC-CO2 was measured statically under various sets of operating conditions in terms of temperature (308–338 K) and pressure (120–270 bar), leading to solubilities in the range of 0.24 × 10−6 to 3.39 × 10−6. Next, three different approaches were followed to estimate, rather than actually measure, the solubility, where models based on two equations of state (i.e., Soave–Redlich–Kwong (SRK) and Peng-Robinson (PR)) combined with either Wong-Sandler (WS) or van der Waals (vdW2) mixing rules, semi-empirical equations (Méndez-Santiago and Teja (MST), Bartle et al., Chrastil, Kumar and Johnston (K-J)), and the activity coefficient (UNIQUAC and modified Wilson models) were adopted to model the experimental data. The semi-empirical models were proved to be self-consistent upon performing the respective self-consistency tests. Eventually, results were devised to calculate estimates of the vaporization (ΔHvap), solvation (ΔHsol) and total enthalpies (ΔHtotal).