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 pK a 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 K ow .