High performance liquid chromatographic analysis of St. John's wort with photodiode array detection.

An RP-HPLC method with photodiode array detection was established for the determination of major constituents (rutin, hyperoside, isoquercitrin, quercitrin, quercetin, pseudohypericin, hyperforin and hypericin) in St. John's Wort dietary supplements. The samples were extracted with methanol by means of sonication in low temperature. The extraction was rapid, with two steps of sonication (30 min each) recovering more than 99% of the major constituents in St. John's Wort samples. The major components were separated by RP-18 chromatography column using a 60-min water-acetonitrile-methanol-trifluoroacetic acid gradient. The quantification was performed by using external standards. Sample preparation and stability of methanolic extract of St. John's Wort were extensively explored. It is worth noting that the major constituents in the methanolic extract of St John's Wort, especially hypericin and pseudohypericin, might be retained by some filter cartridges during the filtration. The current method may serve as a valuable tool for the QA/QC of St. John's Wort dietary supplements.