Signals of diagnostic ions in the product ion spectra of [M − H]⁻ ions of methoxylated flavonoids

Abstract

Rationale: The main feature of the fragmentation of [M − H] − ions of methoxylated flavonoids is the loss of methyl radical (formation of the [M − H − CH 3 ] −• product ion). Subsequent decomposition of [M − H − CH 3 ] −• product ions may be useful for identification of a given compound by HPLC/MS. This paper describes how the selected diagnostic fragment ions can be useful during HPLC/MS(−) analysis of methoxylated flavonoids. Methods: Product ion spectra (ESI-CID-MS/MS spectra) of [M − H] − ions of 17 methoxylated flavonoids (flavones, isoflavones and flavonols) were obtained with a Q-TOF mass spectrometer. Full scan mass spectra (ESI-MS) were obtained with a single quadrupole type of instrument. Results: A number of product ions were recognized as useful from the point of view of structural elucidation. In most cases they were diagnostic product ions, formed as a result of C ring breaking. Conclusions: The most important conclusions drawn from this study are: the product ion at m/z 132 indicates that the analysed compound is an isoflavone; the product ion at m/z 117 indicates the presence of one hydroxy group at ring B or at the 3-position; biochanin A and prunetin can be differentiated by their 'in-source' fragmentation, by the relative abundances of product ions at m/z 195, 183 and 167; loss of mass 102 from the [M − H − CH 3 ] −• ion indicates that ring B is not substituted and there is no hydroxy group at the 3-position; and rhamnetin can be detected using three diagnostic product ions, namely at m/z 121, 165 and 193.

Structural characterization of bioactive compounds in Cotula cinerea extracts by ultra‐high‐performance liquid chromatography with photodiode array and high‐resolution time‐of‐flight mass spectrometry detectors

“…The structures of these compounds were readily assigned through a combination of their UV–vis spectra and high‐resolution mass spectra in addition to the subsequent MS/MS product ions which were in agreement with the proposed structures and the previously reported data for the proposed compounds . The [M − H] − ions of each compound, in addition to those corresponding to product ions involving cleavage of the C‐ring, were in agreement with the proposed structures (Table , Figure ) …”

“…[5][6][7][8][9]24 The [M − H] − ions of each compound, in addition to those corresponding to product ions involving cleavage of the C-ring, were in agreement with the proposed structures (Table 2, Figure 2). 25 All these compounds have been previously reported, 6,9 and their structures were also confirmed using the single ion monitoring acquisition mode which allowed the molecular formulae of the corresponding compounds to be obtained.…”

Identification of isoflavones in the extract of supplements for menopause symptoms by direct infusion electrospray ionization tandem mass spectrometry

“…The first step of the fragmentation of [M‐H] − ions of methoxylated flavonoids is the loss of the methyl radical, thus the formation of the [M‐H‐CH 3 ] −• product ions 31 . At the collision energy 30 eV, in the product ion spectrum of [M‐H] − ion of glycitein standard there is no signal at m/z 283 (ion [M‐H] − of glycitein).…”

“…However, quantitative analysis always has to be preceded by reliable qualitative identification, whereas the qualitative identification of isoflavones is sometimes disputable. 31,32 There is a high risk that the compounds present in the analyzed mixture in low concentrations or characterized by low ESI response will not be detected upon DI/ESI-MS analysis. On the other hand, DI/ESI-MS is definitely less time consuming than LC/ESI-MS.…”

“…It may be argued that qualitative identification of isoflavones in dietary supplements, without their quantitative analysis is out of importance. However, quantitative analysis always has to be preceded by reliable qualitative identification, whereas the qualitative identification of isoflavones is sometimes disputable 31 , 32 …”