Solubility Increment and Thermodynamic Analysis of Bioactive Antofloxacin Hydrochloride in Aqueous ChCl/PTS Deep Eutectic Solvent and Cosolvent Mixtures

The solubility of antofloxacin hydrochloride in deep eutectic solvent (DES) aqueous solutions between choline chloride (ChCl) and p-toluenesulfonic acid (PTS), (ethanol + water), and (ethanol + acetonitrile) cosolvent mixtures were investigated by means of the isothermal dissolution equilibrium method at 273.15–318.15 K under pressure condition of 101.3 kPa. Experimental solubility was strongly increased more than about 560-fold in aqueous ChCl/PTS system with the increasing temperature and mass fraction of DES, and it is 404 times in ethanol + water and 60 times in ethanol + acetonitrile. The solubility maximum 0.01226 (318.15 K, in mole fraction) was obtained in wDES = 0.6 of the aqueous ChCl/PTS DES. X-ray power diffraction (XPRD) was employed to examine the equilibrium solid phase samples of antofloxacin hydrochloride in three systems resulting in no polymorphic transformation, solvate formation or crystal transition compared to the raw sample. The modified Apelblat equation was exclusively used to co...