The phase behavior of a ternary system containing arbutin, which is effective for skin lightening, in a solvent mixture of ethanol and supercritical carbon dioxide (CO2) was investigated. A high-pressure phase equilibrium apparatus equipped with a variable-volume view cell was used to measure the phase equilibrium loci of the ethanol+CO2 binary mixture from 298.2 K to 313.2 K and pressures between 2MPa and 9MPa. The solubility of arbutin in the mixed solvent comprising ethanol and CO2, which equivalently represents the critical locus of T-x, was determined as a function of temperature, pressure, and solvent composition by measuring the cloud points under various conditions. Throughout, the arbutin loading was maintained at 1.5 wt% on a CO2-free basis in the solvent mixture and the pressure and temperature were varied up to 14MPa and 334 K, respectively. For a CO2 loading less than 34wt% on ethanol basis, the cloud point was not observed. However, the solid remained undissolved when the CO2 loading exceeded 54 wt%. Between these loadings, steep and almost pressure-insensitive solubility curves, which extended downward to the vaporization boundary, were found.
Ziegler JW, Chester TL, Innis DP, Page SH, Dorsey JG, in Innovations in supercritical fluids. science and technology, Hutchenson KW, Foster NR Eds., American Chemical Society, Washington, D.C. (1995).