Qualitative and quantitative analyses of quinones in multi-origin Rubia species by ultra-performance liquid chromatography-tandem mass spectrometry combined with chemometrics.

Rubia species are one of the important multi-origin phytomedicines having both economical and medicinal values in many countries. Quinones are the predominant bioactive constituents of these species. Therefore, accurate analysis of these quinones is critical to quality control, clinical, and commercial applications of Rubia species. In this study, a sensitive and efficient ultra-performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (UPLC-QqQ-MS/MS) method in positive and negative multiple reaction monitor (+/-MRM) modes was firstly developed for the characterization of 45 quinones and the quantification of 24 quinones from Rubia plants. The chromatographic separation was achieved on a Waters ACQUITY UPLC® BEH C18 column by using a gradient elution with a mobile phase consisting of 0.1 % formic acid in water and acetonitrile. The results indicated that quinones in multi-origin Rubia samples were different, but 10 quinones existed in all samples. R. cordifolia, which is a unique official medicinal material in Chinese Pharmacopeia, contained the most number of quinones among all the Rubia species. R. podantha and R. sylvatica had the next highest number of quinones, implying that these species could be used as alternatives for R. cordifolia. Chemometric approaches were applied to evaluate the chemical relationship between the Rubia samples based on the constituent quinones. In this study, a UPLC-QqQ-MS/MS method in the MRM mode has been developed for the analysis of Rubia species-derived quinones, which not only contributes to quality control and discrimination of Rubia species, but also suggests the potential of these species in clinical and commercial applications.