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

Rafał Frański; Błażej Gierczyk; Tomasz Kozik; Łukasz Popenda; Monika Beszterda

doi:10.1002/rcm.8316

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

Rapid Commun Mass Spectrom. 2019 Jan 15;33(1):125-132. doi: 10.1002/rcm.8316.

Authors

Rafał Frański¹, Błażej Gierczyk¹, Tomasz Kozik¹, Łukasz Popenda², Monika Beszterda³

Affiliations

¹ Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614, Poznań, Poland.
² NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614, Poznań, Poland.
³ Department of Food Biochemistry and Analysis, Poznan University of Life Sciences, Mazowiecka 48, 60-623, Poznań, Poland.

PMID: 30357940
DOI: 10.1002/rcm.8316

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 - CH₃ ]^-• product ion). Subsequent decomposition of [M - H - CH₃ ]^-• 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 - CH₃ ]^-• 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.