Discrepancies in the German Pharmacopoeia procedure for quality control of Quillaja saponin extracts

Abstract

This study focused on the evaluation of Quillaja saponin extracts with the additional quality designation DAB—which means the abbreviation of the German Pharmacopoeia (Deutsches Arzneibuch). This label suggests that Quillaja saponin extracts marked in this way are of pharmacopoeial quality and thus stand out from other Quillaja saponin extracts. The DAB ninth edition listed Quillaia saponin as a reagent. According to DAB, its quality must be checked by thin-layer chromatography (TLC), and three closely spaced zones in a defined retention factor (Rf) interval specify the saponin reagent. All the Quillaja saponin extracts obtained from different manufacturers and labeled as DAB quality complied with the TLC test. However, the analysis with high-performance liquid chromatography–quadrupole time-of-flight–mass spectrometry (HPLC–Q-ToF–MS) clearly showed additionally an intense peak pattern of Madhuca saponins in all measured samples. The TLC test for Mahua seed cake, which is the press residue from Madhuca longifolia, surprisingly showed the same three closely spaced zones in the defined Rf interval. The three zones could be identified as Mi-saponins from Madhuca after scraping and extracting them from the stationary phase of the TLC plate and subsequent measurement by HPLC–Q-ToF–MS. Therefore, the specification of the saponin reagent in DAB characterizes erroneously Madhuca saponins that are not listed as a saponin plant source for the saponin reagent.