Combination of matrix solid-phase dispersion extraction and direct on-line liquid chromatography-nuclear magnetic resonance spectroscopy-tandem mass spectrometry as a new efficient approach for the rapid screening of natural products: application to the total asterosaponin fraction of the starfish Asterias rubens - Sandvoss,M.; Weltring,A.; Preiss,A.; Levsen,K.; Wuensch,G. (J Chromatogr A, 2001)