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Abstract
The focus of this study was the analysis of the complex chemical composition from different parts of Buddleja davidii, whose species are commonly known as ornamental plants and herbal medicines in many countries. As an herbal medicine, it has been utilized for stroke treatments, headache, wound healing, neurological disorder, etc. However, the understanding of its chemical matrices is still insufficient. Therefore, an online two-dimensional reversed phase liquid chromatography x hydrophilic interaction liquid chromatography (RPLCxHILIC) system coupled with mass spectrometry was applied for further detailed investigation of the chemical constituents in Buddleja dividii. In this two-dimensional liquid chromatography (2D-LC) method, a new at-column dilution (ACD) modulator was introduced in the 2D-LC system to solve the incompatibility problem of the mobile phase between two dimensions, which resulted in a 2D-LC analysis with high orthogonality. For the root extract, as one of the analyzed samples, the optimization of the 1D and 2D gradients was carried out carefully. With this new modulator, much better peak separation and better peak shape were achieved compared to two-dimensional liquid chromatography system using a traditional standard (TS) modulator. With a similar approach, the other four parts of Buddleja davidii were well separated. Comparing the different analyzed parts, flowers and leaves showed the most complex profiles. MS and MS/MS data were obtained successfully, which demonstrated the potential of the proposed RPLCxHILIC-MS system in the constituents’ analysis of herbal medicine. However, due to the lack of reported reference information, 24 compounds could be tentatively identified.
Highlights
In recent decades, as a rising star in the field of chromatography, two-dimensional liquid chromatography (2D-LC) has attracted more and more attention by rapid developments in research of complex systems, such as natural products, environmental pollutants, food and pharmacy, proteomics, and metabolomics [1]
The main reason is that the weak solvent in the 1D consists of a strong eluent solvent for the 2D, which can lead to a problem of mobile phase mismatch and poor or no separation in the 2D
The composition of mobile phase in the early stage of 2D gradient cycle is critical for focusing the transfer analytes on the head of the 2D column
Summary
As a rising star in the field of chromatography, two-dimensional liquid chromatography (2D-LC) has attracted more and more attention by rapid developments in research of complex systems, such as natural products, environmental pollutants, food and pharmacy, proteomics, and metabolomics [1]. Due to the realistic limitation of the transferred volume from the 1D to the 2D, 1D column diameter and flow rate are usually low in LCxLC and a small fraction is collected in the modulator which will be diluted by the 2D high flow rate. In all three described modulators, the fraction dilution factor depends on the length and inner diameter of the sample loop channel and the bypass channel or the length of the trapping and the splitting column This fact involves precise control and optimization of the dilution factor during the analysis of a complex sample containing analytes with a wide range of polarity which can limit the method development. The applicability of ACD modulator is tested for the coupling of RPLCxHILIC-MS system For this propose different parts of the herbal medicine Buddleja davidii were used as an example for the method development. The data could be analyzed by Agilent Mass Hunter Qualitative Analysis Navigator and imported into LC Image 2.7r LC × LC (64bit) to generate MS contour plots
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