Improving Dereplication of Marine Triterpenoid Saponins Using FTIR and LC–MS¹: A Methodological Case Study with <em>Cucumaria frondosa</em>

Marine triterpenoid saponins are structurally diverse metabolites with high pharmacological and nutraceutical potential, yet their characterization remains challenging due to extensive isomerism, aggregation phenomena, and the frequent co-extraction of lipids and other matrix components. In this work, we combine ATR–FTIR and high-resolution LC–MS to investigate the spectral and chromatographic behaviour of Cucumaria frondosa extracts and butanol-enriched fractions. FTIR spectra reveal a strong aliphatic signature, N–H-related features, and ester carbonyl bands consistent with the presence of co-extracted lipids and nitrogen-containing species such as ceramides or sphingolipids. LC–MS analysis of preparative fractions shows recurrent saponin-like ions— most prominently a feature at m/z≈1347—reappearing across chromatographically distinct fractions, often accompanied by lipid-like ions in the 600–900 m/z range. These observations indicate that closely associated lipidic species can modulate the apparent chromatographic behaviour of saponin-containing fractions.