*3.3. Powder Hygroscopicity*

The moisture absorption is a crucial parameter that should be considered during the process of drug development, production, and storage. Therefore, the powder hygroscopicity was measured under 25 ◦C/80% RH condition. Ten days later, the hygroscopic gain of ARI was 0.32 ± 1.30%. Meanwhile, ARI-SAL salt and ARI-ADI salt and its acetone hemisolvate showed greater hygroscopicity, with hygroscopic gains of 2.60 ± 0.78%, 1.36 ± 0.32%, and 1.13 ± 0.7%, respectively. This might be presumably due to the presence of a polar group (i.e., –OH and –COOH) introduced by synthesizing carboxylate salts, leading to the formation of hydrogen bonds with water molecules [33].
