LC-DAD-MS/SPE-NMR hyphenation, a tool for the analysis of pharmaceutically used plant extracts: identification of isobaric glycoside regioisomers from Harpagophytum procumbens - Seger,C.; Godejohann,M.; Tseng,L.H.; Spraul,M.; Girtler,A.; Sturm,S. (Anal Chem, 2005)