Quercetin fragment ions

As a result of the low concentration of flavanols in blood fractions such as plasma when food level doses are consumed, there are only a few techniques that have sufficient sensitivity. The first of these is gas chromatography coupled to a mass spectrometer for detection [88]. This technique is quite sensitive and provides the assurance of accurate identification of the analyte when the molecular and major fragmentation ions are monitored. The drawbacks are that it is necessary to derivatize the flavanols to achieve sufficient volatility and the technique cannot be adapted for analysis of glucuronide and sulfate conjugates. This method has been used to quantify the plasma levels of catechin and its methylated derivatives after wine consumption, and a modified version is able to detect catechin, quercetin, and resveratrol simultaneously [89]. 

Fig. 2.57. Identification of a flavonoid diglycoside from unhydrolized chokeberry sample, (a) Positive total ion chromatogram, (b) ion source collision-induced dissociation chromatogram for the ion m/z 303 (quercetin), (c) full scan MS spectrum of the peak at 14.1min, (d) full scan MS-MS spectrum of the [M+H] ion, (e) fragmentation spectrum (MS3) of the m/z 303.3 ion. Reprinted with permission from S. Hakkinen et al. [161].

Hvattum [48] reported the analysis of varions phenolic compounds in Rosa canina using LC-DAD, negative-ion LC-ESI-MS, MS-MS on [M-H] , and MS-MS on fragments generated by in-source CID. In this way, the aglycones catechin and quercetin, and various glycosides of quercetin, taxifolin, and eriodictyol were identified as well as some other plant phenol compounds. 

Figure 4 Product ion spectra of epicatechin-O-glucuronide (top) and quercetin-0-glucuronide. Whereas the spectrum for quercetin-O-glucuronide only shows the neutral loss of glucuronic acid (m/z 303), the spectrum for epicatechin-O-glucuronide shows—apart from the loss of water and other small molecules— several characteristic fragments like [ A -i-glucuronic acid]" (m/z 315).

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