Identification of major and minor constituents of Harpagophytum procumbens (Devil's Claw) using HPLC-SPE-NMR and HPLC-ESIMS/APCIMS - Clarkson,C.; Stærk,D.; Hansen,S.H.; Smith,P.J.; Jaroszewski,J.W. (J Nat Prod, 2006)