Objective To determine the best dissolution medium of Cassiae Semen extract, analyze the contribution degree of the main components in Cassiae Semen extract to equilibrium solubility in the optimal dissolution medium, and clarify the markers of equilibrium solubility of Cassiae Semen extract.

Methods The equilibrium concentrations of Cassiae Semen extract were determined at different time points in water, 0.1 mol/L hydrochloric acid and pH 6.8 phosphate buffer at 37 ℃ by differential spectrophotometry with taking the content of total anthraquinone as the index, and the optimal dissolution medium was determined.The equilibrium concentration fingerprint of Cassiae Semen extract at different equilibrium time points in the optimal dissolution medium was established by HPLC, and the markers of equilibrium solubility of Cassiae Semen extract were screened.

Results The equilibrium solubility of Cassiae Semen extract in water, 0.1 mol/L hydrochloric acid and pH 6.8 phosphate buffer at 37 ℃ was 10.344, 10.910 and 11.099 μg/mL, respectively.The time to reach the equilibrium time point was 24 h, 3 h and 7 h, respectively.In the optimal dissolution medium, there were 22 chemical components with VIP value greater than 1, of which the chemical components were the known components aurantio-obtusin, rhein, emodin, chrysophanol and physcion, which ranked first, second, fifth, ninth and thirteenth, respectively.

Conclusions pH 6.8 phosphate buffer is the best dissolution medium of Cassiae Semen extract.The equilibrium solubility of Cassiae Semen extract can be investigated by using aurantio-obtusin, rhein, emodin, chrysophanol and physcion as solubility markers.