ABSTRACT
Objective To determine the solubility of rhein in different vehicles and its partition coefficients in the n-octanol-water system for designing new formulations. Methods High performance liquid chromatography(HPLC) method was established to determine the concentration of rhein in water,different pH solutions and different solvents;the partition coefficients for the n-octanol- buffer solution systems were determined by shaking flask method. Results The equilibrium solubility of Rhein was 3.89 μg·mL-1and the lgP was 2.79 in water at 37 ℃.The solubility of rhein was increased with the raise of pH, which could reach 362.20 and 431.65 μg·mL-1in phosphate buffer solution at pH 6.8 and 7.4,respectively.Solubility of rhein in the semi polar solvent was relatively good,which can up to 2 971.74 μg·mL-1in PEG400.The oil-water partition coefficients of rhein were decreased with the increase of pH,and were 0.83 and 0.54 in phosphate buffer solution at pH 6.8 and 7.4,respectively. Conclusion Rhein is almost not soluble in water.With the raise of pH,the solubility is increased but the oil-water partition coefficient is decreased.