SOLUBILITIES OF THE XANTHINES CAFFEINE, THEOPHYLLINE AND THEOBROMINE IN SUPERCRITICAL CARBON-DIOXIDE

An apparatus for the experimental determination of the equilibrium sol ubilities of solids in dense gases is described. Determination of solu bilities has been performed by using a static analytical method with d irect coupling of an equilibrium cell to a supercritical fluid chromat ographic (SFC) system. The solubilities of caffeine, theophylline and theobromine in supercritical carbon dioxide were measured at different temperatures (313, 333 and 353 K) and over a pressure range of 20-35 MPa. Although the chemical structures of the xanthines are very simila r, their solubilities in supercritical carbon dioxide vary substantial ly. The solubilities of caffeine in CO2 are one order of magnitude hig her than those of theophylline and two orders of magnitude higher than those of theobromine. Solubility values obtained in this work are com pared with published data. Reasons for observed differences are discus sed.