Simultaneous determination of components with wide polarity and content ranges in Cistanche tubulosa using serially coupled reverse phase-hydrophilic interaction chromatography-tandem mass spectrometry

Abstract

To meet the demands from plant physiologists and pharmacognosists, sustainable efforts are being devoted by the analytical chemists from all over the world to search an approach being capable of simultaneously monitoring primary along with secondary metabolites. The key technical bottlenecks currently lie at affording satisfactory chromatographic and spectrometric performances for both hydrophilic and hydrophobic substances that span a great content range. Herein, reverse phase liquid chromatography was directly coupled with hydrophilic interaction chromatography, namely RPLC-HILIC, to integrate their merits, whereas dilution pumps were employed to tackle the mismatching for the mobile phase between them. On the other side, inferior parameters rather than the optimal ones were applied for those abundant ingredients to advance the upper limits of quantitation, such as echinacoside (1250.0μg/mL), mannitol (100.0μg/mL), and acteoside (125μg/mL), in mass spectrometer domain. As a desert parasitic plant as well as tonic materials, Cistanche tubulosa (CT) has drawn widely interests from plant physiologists and pharmacognosists regarding its quantitative metabolome. Simultaneous determination of 23 abundant and minor ingredients covering most chemical families in CT, i.e. amino acid, nucleoside, organic acid, phenylethanoid glycoside, lignan, and iridoid, was attempted to understand the physiologic patterns as well as pharmacological values of the crude materials. Although the analytes spanned wide polarity (-3.326≤cLogP≤1.421) and content (more than 5 orders of magnitude) ranges, satisfactory chromatographic and spectrometric behaviors were gained for all analytes. Reliable quantitation was demonstrated via various method validation assays, such as recovery, linearity, sensitivity, and precision. The contents of 23 hydrophilic and hydrophobic substances were quantified in 20 batches of CT. Significant variations occurred for the contents of those components. Echinacoside (1.35-387.50mg/g) was usually observed as the most abundant component, whereas ferulic acid (<0.0043mg/g) always exhibited trace distributions. Above all, the integrated equipment setup could serve as a fit-for-purpose tool for in-depth quality evaluation of CT and more importantly, for comprehensively understanding the metabolome of plants.

Keywords: Cistanche tubulosa; Serially coupled reverse phase-hydrophilic interaction chromatography; Simultaneous determination; Upper limit of quantitation; Wide polarity span.