Characterization and determination of compounds in willow bark using HPLC-MS and mf-MELDI-MS

Willow bark (Salix sp.) is officinal in German Pharmacopeia and approved in the Commission E monographs. It is used as a main component of analgesic and anti-rheumatic drugs. Constituents of willow bark include 1.5–11% of phenolic glycosides, mainly salicylates (1.0–10.2%), including salicin and its derivatives (salicortin and tremulacin), 8–20% of tannins, mainly catechin tannins, some gallotannins and condensed tannins (procyanidins) and 1–4% of flavonoids, including isoquercitrin and naringin and its glycoside. The aim of this study was the qualitative and quantitative analysis of target compounds relevant for the pharmacological activity of Salix extracts using high performance liquid chromatography-mass spectrometry (HPLC-MS) and matrix free-material enhanced laser desorption ionization-mass spectrometry (mf-MELDI-MS). A special purification protocol was used to purify the extracts for identification of compounds in Salix extracts. Employing polyamide column, Sephadex LH-20 column and Sep-Pak C18 SPE cartridges fractions were obtained, containing phenolic acids, flavonoid glycosides, monomeric catechins, oligomeric procyanidins and polymeric procyanidins. Qualitative analysis was performed by HPLC-MS and mf-MELDI-MS. Especially mf-MELDI-MS was suitable for qualitative investigation, as it delivered data in few minutes with accurate mass identification. For quantification several SPE cartridges were evaluated to gain highly purified fractions prior to HPLC analysis. Strata-X SPE cartridge delivered highest amounts of interesting compounds and yielded purified samples.

Acknowledgement: A scholarship BMWF (Technology Grant) for S.K. is gratefully acknowledged