AIMTo study the thermodynamics of precipitation reaction and kinetics between berberine and rheinic acid. The former is the main compound in rhubarb root or corktree bark, the latter is a representation of anthraquinone compounds that are the main kind compound in coptis rhizome. The precipitate produced in preparation of complex prescription of Chinese herbal medicines Xiexin decoction and Shaoyao decoction had made an appeal. The work should build a good basement for two decoctions research and development.

METHODSCapillary electrophoresis (CE) and front analysis methods are used for determining two compounds' equilibrium concentration at different precipitate conditions to calculate the constants of thermodynamics and kinetics.

RESULTSThe molar ratio of berberine and rheinic acid in precipitate is 1:1. The solubility product constant Ksp = [B] [R] = (3.29 +/- 0.19) x 10(-9) mol2.L-2. The precipitate reaction is an endotherm process and Ksp shows less effect by temperature. The reaction occurred immediately even though the precipitate cannot be observed in time. The precipitate process in experiments is practically just an aging or grown process of the precipitate particles. High temperature can quicken the aging.

CONCLUSIONThe precipitate in Chinese herbal medicines Xiexin decoction and Shaoyao decoction should be resulted from anthraquinone compounds and alkaloids. The reproductivity of capillary electrophoresis can be improved for simple sample by combining peak height measurement.