Two different approaches, i.e. fast-atom bombardment tandem mass spectrometry and gas chromatography combined with mass spectrometry (GUMS) have been employed for the characterization of a mixture of biologically relevant polyphenols (kaempferide, kaempferol, luteolin and oleouropein). The best results have been achieved by the first approach which allows an easy structural identification of the different compounds, also in the presence of isomers. G U M S of the trimethylsilyl derivatives leads to a complex chromatogram due to the presence of derivatives exhibiting a different level of silylation; the only species related to oleouropein are due to pyrolysis products (silylated fragments of sugars) and there is no evidence for the related silylated aglycone.Polyphenol compounds are widely distributed in the plant kingdom'.' and can be divided into different classes such as phenolic acids and derivatives, coumarins, flavonols, anthocyans, tannins and so on. In particular, flavonoids show a wide range of biochemical and pharmacological effects3 and consequently the structural characterization of these compounds represents a topic of wide interest.For such reasons, many papers have appeared on the mass spectrometric behaviour of these compounds, as well as on the results achievable with different mass spectrometric approaches.A series of papers, due to Guidugli et al. ,4-7 describe in great detail the behaviour of flavones, naphthoflavones and flavanones. In the first of them, the electronimpact (EI) induced fragmentation pattern of flavone has been fully elucidated by means of accurate mass measurements, metastable ion studies and deuterium labelling experiments; a particular emphasis was devoted to the mechanism of the [M-HI+ ion formation in substituted flavones. In a further paper,5 the structure of the [M-HI' ion of dibenzo-b-tropolone was proved by means of extensive deuterium labelling and comparison of linked-scan spectra. In the case of naphthoflavones,' the CO loss and the retruDiels-Alder processes were found to be characteristic.While EI is highly effective for the structural characterization of flavone and its derivatives with non-highly polar substituents, it shows severe limitations in the case of flavonols and related plant phenolics, as well as for 0-and C-glycosides because of their low volatility and poor thermal stability. For such reasons their derivatization becomes essential before examination, and methylationx-15 and trimethylsilylation'6,'7 pro-* Author for correspondence.cedures have been proposed; using such approaches the analysis of flavonoid-containing complex mixtures by gas chromatography/mass spectrometry (GUMS) became possible."For the analysis of underivatized compounds, field desorption was first proposed," but with the introduction of the fast-atom bombardment (FAB)" technique, mass spectra of underivatized compounds were more easily obtained. The first paper on FAB of a series of underivatized flavonol aglycones and glycosides is due to de Koster et ~1 .~' These authors focused ...
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