Physicochemical Studies on Decoctions of Kampo Prescriptions. II. Relationship between the Hydrophobic Parameter of the Crude Drug Components and Their Transfer Ratio into the Decoctions.

Abstract

Assuming that the general partition of crude drug components between oil and water can be replaced by that between the crude drug residue and the decoction solution, the following equation can be derived linking the transfer ratio (rT) of the components and the capacity factor (k') on reverse-phase HPLC : log (100/rT-1)=alogk'+b In this equation, a and b are constants when the method of preparation of decoctions and the HPLC conditions are kept constant. In order to verify this relationship, some model decoctions were prepared using small size preparations (0.5-1.0mm) of crude drugs, and the correlation between log (100/rT-1) and logk' of the components was examined. Since the correlation coefficient of the equation was calculated to be 0.9 or higher in these model decoctions, the assumption was useful for investigating this relationship between the transfer ratio and the hydrophobic or related parameters. Thus, the transfer ratios of all components in a decoction could be evaluated as a single continuous line rather than an aggregation of single points for the transfer ratios, and most of the highly hydrophobic components could be transferred to the decoctions without dissolution in water.