The determination of dissociation constants for active ingredients from herbal extracts using a liquid–liquid equilibrium method

A liquid–liquid equilibrium method to determine dissociation constants was presented in this work using phenolic acids in the water extract of Salvia miltiorrhiza as a sample. The models to quantitatively describe the relationship between aqueous phase pH value and apparent distribution coefficient value were built. Apparent distribution coefficients are determined after liquid–liquid equilibrium experiments. The pKa values of phenolic acids in S. miltiorrhiza extracts were fitted successfully. The dissociation constants of active ingredients that are in a mixture in which most components are unknown can be determined using this method. The distribution coefficients of active ingredient molecules and ions can also be obtained. 1-Octanol is a recommended solvent with low solubility, high boiling point, and extra information of Kow.