Determination of hyperforin in mouse brain by high-performance liquid chromatography/tandem mass spectrometry - Blume, Henning H.; Dingermann, Theodor.; Eckert, Gunter P.; Karas, Michael.; Keller, Jan-Henning.; Muller, Walter E.; Schubert-Zsilavecz, Manfred.; Tawab Mona Abdel.; Volmer, Dietrich A.