Validation of a greener procedure for the extraction of triterpenic acids from Hedyotis corymbosa

Abstract A hyphenated procedure (HUAE) of ultrasound-assisted extraction (UAE) and heat-reflux extraction (HRE) was developed and validated to extract oleanolic acid (OA) and ursolic acid (UA) from Hedyotis corymbosa. High-performance liquid chromatography and ultraperformance liquid chromatography/mass spectrometry were utilized to analyze the extracts. The HUAE procedure not only provided higher yields but also demanded less organic solvent and time at a lower temperature than HRE and UAE alone. Furthermore, the kinetic data of UA obtained from HUAE and HRE are excellently fitted by the second-order kinetic model, indicating that the fitting parameters obtained by HUAE, such as the extraction rate constant, initial extraction rate and equilibrium concentration, were higher than those obtained by HRE. The activation energies derived by HUAE and HRE of UA from H. corymbosa were 9.62 and 11.88 kJ/mol, respectively, showing that the energy barrier required for HUAE was significantly lower than that for HRE. Derivation from Fick's second law indicated that the mass transfer, diffusion coefficients and equilibrium constant acquired from the HUAE of UA were significantly greater than those obtained from the HRE, which further confirmed the superior efficiency of the HUAE procedure. The obtained thermodynamic properties, such as the enthalpy, entropy, and Gibbs free energy, obviously demonstrated that the HUAE and HRE of UA from H. corymbosa were endothermic and irreversible processes; the rate-controlling step was the internal mass transfer.