Study on fragmentation patterns of coumarins in Notopterygium inchum with ultrahigh performance liquid chromatography combined with quadrupole time-of-flight mass spectrometry

Abstract

To demonstrate the fragmentation patterns of simple coumarins furanocourmarin(C_7-C_8), furanocourmarin(C_6-C_7) and dihydrofuran coumarin by mass spectrometry, with fraxin, scopoletin, isopsoralen, pimpinellin, isoimperatorin, notopterol and noda-kenin as study subjects, so as to provide a basis for rapid identification of compounds in different subtypes of coumarins. Ultrahigh performance liquid chromatography combined with quardrupole time-of-flight mass spectrometry(UPLC-Q-TOF-MS) was implemented in both positive and negative ion modes. Masslynx software was employed to provide the elemental constituents of each detected ion based on its accurate molecular weight. Chemdraw 2014 was used to cultivate mass number of each inferred structure. The fragment pattern of each compound was determined based on the structures inferred from all the relevant ions. And the patterns were drawn by Chemdraw 2014. The deviation between the calculated molecular weight of the inferred structure and the detected value of the ions was used to assess the correctness of the inferred structures in the fragmentation patterns. The results showed that with UPLC-Q-TOF, neutral loss of CO_2 and CO was reflected in lactone and furan skeletons from the courmarin structure. An even mass was attributed to the loss of an odd number of methyl radicals from compounds with a methoxy substituent. Furanocourmarin(C_7-C_8) produced a protonated molecular ion([M+H]~+), while the other courmarin subtypes produced either a sodium adduct of the molecular ion([M+Na]~+) or a sodium adduct of the molecular ion([M+Na]~+) with a protonated molecular ion([M+H]~+). The m/z 203.03 was a diagnostic ion for furanocourmarin(C_6-C_7), and the m/z 147.04 was supplementary evidence for furanocourmarin(C_6-C_7) identification. The characteristic ion of furanocourmarin(C_7-C_8) was m/z 131.05, while m/z 187.04 was the characteristic ion of dihydrofuran coumarin. The m/z 203.03 ion for furanocourmarin(C_7-C_8) was pretty weak. In negative ion mode, furanocourmarin(C_7-C_8) did not have any signals that were different from the other subtypes of courmarins. The fragmentation patterns in negative ion mode for the other subtypes of courmarins were similar to those in positive ion mode. Four types of fragmentation patterns were identified as forcourmarins from Notopterygium inchum. This study provides the basis for the rapid identification of courmarin subtypes by mass spectrometry.