A simple and precise method was established for the determination of honokiol (I) and magnolol (II) in kampo medicines containing Magnolia Barks using high-performance liquid chromatography with tetra-n-amylammonium bromide (TAA) as an ion-pair reagent. The optimum conditions for extracting both components from these kampo medicines were 15-min reflux with methanol. I and II were eluted within 9 min and 12 min, respectively, without interference from co-existing components using an ODS column and a mixture of water-acetonitrile containing 10 mM TAA as a mobile phase.
