Microextraction assisted multiple heart-cutting and comprehensive two-dimensional liquid chromatography hyphenated to Q-TOF/MS for the determination of multiclass compounds from Dendrobium species

Abstract

Chromatographic separation and determination of closely related classes are one of the most difficult tasks in the analysis of medicinal plants. In addition, two-dimensional ultra-high performance liquid chromatography (2DLC) has enormous potential and become a significant tool for enhancing peak capacity, selectivity and sensitivity. Workflows based on multiple heart-cutting (MHC) and comprehensive 2DLC (LC × LC) hyphenated to quadrupole time-of-flight mass spectrometry (Q-TOF/MS) were described that allow to identify and separate the analytes in Dendrobium species. Three Dendrobium genus were Dendrobium officinale Kimura et Migo, Dendrobium nobile Lindl and Dendrobium chrysotoxum Lindl. In this study, excellent selectivity, resolution, and peak shape were obtained through combining reversed-phase SB C18 column (2.1 × 100 mm, 1.8 μm) in the first dimension with 3.0 × 50 mm Poroshell 120 Bonus column (1.8 μm particle size) in the second dimension (2D), together with the application of synchronized mode in both dimensions. The matrix solid phase dispersion method was applied to extract Dendrobium species and 31 compounds were characterized and separated within 40 min. In terms of 2D flow rate and separation, LC × LC mode was faster than MHC mode. However, too high 2D flow rate would exacerbate the damage to the column in the LC × LC mode. MHC mode was used to genernally separate and analyze specific parts of the sample, otherwise it would take too much time. In short, MHC and LC × LC coupled with Q-TOF/MS method was a powerful technique and shown to be applicable for the analysis and determination of trace compounds in Dendrobium genus extracts and could be easily expanded to other complex mixtures.