Calculating Critical Relative Humidity from Solubility According to Pitzer Ion Interaction Model

The solubility and the critical relative humidity (H-er) of 14 drugs and inorganic salts were determined, the relationship between the H-er and the solubility was explored theoretically, and the H-er was calculated in the light of Raoult's law and Pitzer ion interaction model from their solubility. The results indicate that the H-er values calculated by Raoult's law in high humidity (H-er > 80%) and by Pitzer ion interaction model in low humidity (H-er < 80%) are comparable to the measured ones.