*3.5. Solubility*

3.5.1. Equilibrium Solubility Test

The results of the equilibrium solubility experiments are summarized in Figure 9. The equilibrium solubility of the ARI-ADI salt in water, hydrochloric acid buffer, and acetate acid-sodium acetate buffered solution were 0.13, 0.63, and 0.15 mg/mL, respectively, which was much better than that of the ARI and ARI-SAL salt but slightly smaller than that of the ARI-ADI salt acetone hemisolvate. However, the equilibrium solubility of the ARI-SAL salt was even worse than that of the ARI in both the hydrochloric acid buffer solution and acetate acid-sodium acetate buffered solution, though slightly better in water. In addition, the equilibrium solubility of ARI and its salts in the phosphate buffer solution were too low to be acquired accurately.

**Figure 9.** The equilibrium solubilities of ARI and its crystal salts in different solutions. **I**: water (pH 7.0); **II**: hydrochloric acid buffer (pH 1.2); **III**: acetate acid-sodium acetate buffered solution (pH 4.5).
