Electrospray ionisation mass spectrometric behaviour of flavonoid 5‐O‐glucosides and their positional isomers detected in the extracts from the bark of Prunus cerasus L. and Prunus avium L

Introduction Literature data concerning the electrospray ionisation mass spectrometry (ESI‐MS) behaviour of flavonoid 5‐O‐glycosides are poor and sometimes disputable. Therefore, we decided to analyse the compounds of this kind present in the bark of Prunus cerasus and Prunus avium by using high‐performance liquid chromatography HPLC/ESI‐MS. Objective The aim of this study is to obtain the comprehensive information about the ESI‐MS(+/−) behaviour of flavonoid 5‐O‐glucosides, to compare their behaviour with that of their positional isomers, to confirm that the known susceptibility of flavonoid 5‐O‐glucosides to hydrolysis may be successfully used for their identification. Method The bark from Prunus trees was extracted with pure methanol or, in order to perform hydrolysis and extraction simultaneously, with 5% methanolic solution of hydrochloric acid. The HPLC‐ESI‐MS analyses were performed using a Waters model 2690 HPLC pump and Waters/Micromass ZQ2000 mass spectrometer. Results Flavonoid 5‐O‐glycosides were completely hydrolysed under the acid conditions used, in contrast to their positional isomers. In positive ion mode, at low cone voltage, flavonoid 5‐O‐glycosides yield abundant Y0+ aglycone ions, in contrast to their positional isomers. In the negative ion mode, flavonoid 5‐O‐glycosides do not yield [Y0 − H]−· fragment ions, in contrast to their positional isomers. When aglycone contains only two hydroxyl groups, the flavonoid 5‐O‐glycosides can be detected in negative ion mode, whereas their positional isomers do not yield [M − H]− ions. Conclusion It has been demonstrated that the susceptibility to hydrolysis of the analysed compounds, the abundances of respective fragment ions formed, and their ESI(−) response allow unambiguous identification of flavonoid 5‐O‐glycosides and their differentiation from their positional isomers. A number of flavonoid 5‐O‐glucosides (e.g. chrysin 5‐O‐glucoside) and their positional isomers (e.g. chrysin 7‐O‐glucoside) present in the bark extracts of Prunus cerasus and P. avium, have been analysed by using high‐performance electrospray ionisation mass spectrometry (HPLC‐ESI‐MS) (+/− mode). It has been demonstrated that the susceptibility to hydrolysis of the analysed compounds, the abundances of respective fragment ions formed, and their ESI response in negative ion mode allow unambiguous identification of flavonoid 5‐O‐glycosides and their differentiation from their positional isomers.