Determination of Equilibrium Solubility and Apparent Oil/Water Partition Coefficient of Ursolic Acid

OBJECTIVE To determine the equilibrium solubility of ursolic acid and its partition coefficients in the n-octanol-water system for designing new formulations．METHODS High performance liquid chromatography (HPLC) was established to determine the contents of ursolic acid in different pH solutions, differernt solvents and the partition coefficients for the n-octanol- water systems. RESULTS The equilibrium solubility of ursolic acid was 5.64 mg·L^-1 in water at 25 ℃ and was not influenced by the pH of the buffer solution. The solubility of ursolic acid in oils was poor, but was relatively good in surfactants and Semi polar solvents. Partition coefficient of ursolic acid was 2.17 in n-octanol-water system. CONCLUSION Ursolic acid is a lipophilic drug with little solubility property.