MEASUREMENTS OF SOLUBILITIES OF XANTHINES IN SUPERCRITICAL CARBON-DIOXIDE PLUS METHANOL

Solubilities of the xanthines caffeine, theophylline, and theobromine in different supercritical (carbon dioxide + methanol) mixtures were m easured at 313 K and 22 MPa. The solubilities of theobromine in superc ritical carbon dioxide + methanol were also measured at 333 K and 22 M Pa. The determination of solubilities has been performed by using a st atic analytical method with direct coupling of an equilibrium cell to a supercritical fluid chromatographic system. The solubility of all xa nthines was enhanced by adding methanol to the fluid. For example, wit h 0.1 mass fraction of methanol in the fluid mixture the solubility of every xanthine increases by 1 Order of magnitude. Although the chemic al structures of the xanthines are very similar, their solubilities in supercritical carbon dioxide mixtures, as in pure carbon dioxide, var y substantially. The solubilities of caffeine in CO2 are 1 order of ma gnitude higher than those of theophylline and 2 orders of magnitude hi gher than those of theobromine.