A new LC-MS assay for determination of triterpene glycosides in Cimicifuga racemosa avoiding overestimation problems during stability testing

Determination of triterpene glycosides (TGs) in the rhizomes and rhizome extracts of Black cohosh, Actea racemosa L. (syn. Cimicifuga racemosa (L.) Nutt.) according to the monograph of the European Pharmacopoeia (EP) is executed by HPLC. Due to the lack of characteristic chromophores in their structure, the analytes could be better detected and quantified by evaporative light scattering detection (ELSD) [1]. Beside a poor precision and sensitivity, a limited working range and the impossibility of any identity proof for the analytes, the ELSD-assay has the disadvantage of very different responses of the individual TGs. In connection with spontaneous rearrangement reactions [2] even in dry extracts and tablets, this leads to overestimation of the total amount of TGs during stability testing. Deviating from the EP method, which used only one external standard, the new proposed UPLC-MS assay determines about 30 TGs in four mass tracks with four external standards. Each of them is a characteristic representative for a different group of TGs forming a characteristic cardinal fragment already at the ion source of the mass spectrometer. In contrast to ELSD detection, all TGs respectively their cardinal fragments in the particular group give very similar responses in the MS-detector. The peak areas of TGs in each mass track are evaluated by comparison to the area of the respective assigned external standard. In this way apparent fluctuations in content, attributable to rearrangements of the triterpene glycosides, are avoided. The method is therefore more suitable for stability testing than the method proposed by the EP.