Correlation for the solubilities of pharmaceutical compounds in supercritical carbon dioxide

The solid solubilities of pharmaceutical compounds in supercritical carbon dioxide were correlated using the regular solution model with the Flory–Huggins equation. The pharmaceutical compounds include steroids, antioxidants, antibiotics, analgesics and specific functional drugs. The molar volumes of these solid solutes in supercritical carbon dioxide were taken as the empirical parameters in this study. They were optimally fitted for each pharmaceutical compound using the experimental solid solubility data from literature. The logarithms of the molar volumes of these solutes were then correlated as a linear function of the logarithms of the densities for supercritical carbon dioxide. With one or two parameters in this linear equation, satisfactory solid solubilities were calculated that were comparable to those from the commonly used semi-empirical equations with more adjustable parameters. The parameters of this model were further generalized as a function of the properties of the pharmaceutical compounds. It was observed that the prediction of solubilities of pharmaceutical compounds in supercritical carbon dioxide was within acceptable accuracy for more than 50% of the systems investigated in this study.