Fast and simultaneous determination of four index components in Qingwei Huanglian tablets by RP-HPLC Determination of berberine hydrochloride, epiberberine, jatrorrhizine, palmatine, and glyeyrrhizinate in Coptidis Rhizoma Compound Decoction by HPLC Determination of berberine hydrochloride, epiberberine, jatrorrhizine, palmatine, and glyeyrrhizinate in Coptidis Rhizoma Compound Decoction by HPLC