Fast Separation and Sensitive Quantitation of Polymethoxylated Flavonoids in the Peels of Citrus Using UPLC-Q-TOF-MS

A rapid, sensitive, and efficient ultraperformance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) method has been developed to analyze polymethoxylated flavonoids (PMFs) in 14 Citrus peels, including 7 Citrus reticulata (C. reticulata) and 7 Citrus sinensis (C. sinensis). In this study, fast separation can be achieved within 12 min and 42 PMFs have been identified including 33 flavones and 9 flavanones. Most C. reticulata were shown to contain more than 20 PMFs, except Guangxihongpisuanju (GX) containing only 12 PMFs, while most C. sinensis contained fewer than 20 PMFs, except Edangan (EG) containing as many as 32 PMFs. To our knowledge, there are few reports about the quantitation of PMFs using the MS response. Here, a MS quantitative method was established and systematically validated in linearity, precision, and recovery. The linearity was from 1.25 ng/mL to 1.0 μg/mL with the limit of detection (LOD) as low as 75 pg/mL and the limit of quantitation (LOQ) as low as 0.25 ng/mL. Up to 13 PMFs, more types than ever before, were undoubtedly identified and quantitated according to the PMF standards. The results showed that the contents of PMFs in the C. reticulata were generally higher than those in the C. sinensis. This study is systematic for analyzing PMFs and is of great significance because it can provide guidance on utilization of both PMFs and citrus germplasm resources in the future.