MALDI-TOF mass spectrometry and reversed-phase HPLC-ELSD chromatography for structural and quantitative studies of major steroid saponins in commercial extracts of Yucca schidigera Roezl

Abstract

This paper describes a new, improved systematic qualitative analysis of yucca saponins in commercial products by combined use of high-pressure liquid chromatography (HPLC) coupled to an evaporative light scattering detector (ELSD) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). Three groups with four saponins in each were completely resolved by HPLC-ELSD under C18 reversed-phase conditions using a linear gradient composed of methanol and water. The selectivity of the described HPLC-ELSD method is given by the sapogenin differences at C12 (carbonyl group) and at C2 (hydroxyl group), followed by the presence or absence of an exomethylene group at C25, and the composition and length of the oligosaccharidic chain at C3 in the sapogenins. The saponins were identified by chemical and spectroscopic methods including MALDI-TOF MS1 and MS2, high resolution MS, and one and bi-dimensional nuclear magnetic resonance (NMR) experiments. Among the twelve saponins identified, eleven were previously reported, and one is reported for the first time in Yucca schidigera. An identification flowchart procedure based on the analysis of the sodium adducts of intact saponins [M+Na]+ and the oligosaccharidic chain ions obtained in the MALDI-TOF MS1 and the MS2 spectrums, was developed for the analysis of Y. schidigera saponins. Two intact isomeric saponins were differentiated by this method, which could also be applied to the structural assignment of other steroid and triterpenic saponins. Using the four-major saponins as reference standards, a C18 reversed-phase HPLC-ELSD method was validated for their specific analysis in commercial extracts of Y. schidigera. Finally, the applicability of the HPLC-ELSD method for the relative quantification of yucca saponins is discussed.