Revisiting the fragmentation mechanism of catechin isomers

Abstract

AbstractIntroductionThe reason for the neutral loss of 44 Da in catechin tandem mass spectrometry analysis is not yet clear. Past studies used low‐resolution mass spectrometers, which made isobaric ions easily misjudged or ignored. One of the important fragment ions [(epi)Catechin‐H+‐44]− is usually determined to be derived from the loss of C2H4O (MW = 44.0262) at the C‐ring of catechin anion. However, in the results of high‐resolution mass spectrometry, this ion is m/z = 245.0808, which does not meet the expected theoretical value (m/z = 245.0454). Because this ion should be the parent ion losing CO2 (MW = 43.9898), not C2H4O. Therefore, it is necessary to re‐deduce the structure and generation path of fragment ions.MethodIn this study, high‐resolution mass spectrometry was used to analyze and compare the mass fragmentation differences of phenol, phloroglucinol, and three dihydroxybenzene isomers to establish the source of CO2‐neutral loss of catechins.ResultIt was found that both phloroglucinol and resorcinol, which have the same structure as the A‐ring of catechin, can generate [M‐H+‐CO2]− fragment ions, while phenol, hydroquinone, and catechol are not.ConclusionsIt is demonstrated that the part of catechin anion contributing to CO2 neutral loss is the A‐ring rather than the B‐ring.