Procyanidins fragmentation

FIGURE 5.8 Mass fragmentation patterns of malvidin 3-glucoside-procyanidin B2 3 -gallate adducts. 

Tandem mass spectrometry or MS/MS is frequently used for structural elucidation of phytochemicals to provide more detailed information about the structure and composition of a molecule. This involves two mass spectral steps and fragmentation of the compound occurs between the steps. The two steps may be separated in space or in time depending on whether two distinct separation elements are used (space) or two different separations occur in the same place over time. As described previously, an IT analyzer can be used to successively fragment a molecule to provide MS" spectra, an example of separation in time. A triple quadrupole mass spectrometer is a form of tandem mass spectrometry in space in which two quadrupoles serve as mass filters while a third, positioned in the middle, allows for collision-induced dissociation. Triple quadrupoles are common in phytochemical analysis, and have been used to characterize phenolic compounds in fruit juices (Abad-Garcia et ah, 2009) and procyanidins and alkaloids in cocoa (Ortega et ah, 2010), among others. 

Procyanidin dimer, trimer, tetramer, and pentamers have molecular masses of 578, 866, 1154, and 1442, respectively. They can be easily identified using a mass spectrometer if [M H] m/z 577, 865, 1155, or 1441 are observed. Proanthocyanidins have three fragmentation... 

Figure 3.8 Fragmentation patterns of A-type procyanidin trimers by LC/ESI-MS in negative-ion mode...

The positive-ion mode fragmentation patterns proposed for trimeric procyanidins studied by isolation and ion trap fragmentation of the most intense MS spectra signals, fragmentation of the principal ions of the MS2 spectra, and acquisition of MS3 spectra, are shown in Fig. 6.14 (Pati et al., 2006). In Figs. 6.15 and 6.16, the schemes of positive... 

Figure 6.13. Schemes of A-type procyanidin trimers fragmentation observed by LC/ ESI-MS negative-ion mode.

Figure 6.14. Positive-ion mode fragmentation patterns of trimeric procyanidins. The ESI-MS conditions spray voltage 4.5 kV sheath gas nitrogen 0.9L/min capillary voltage 35 V capillary temperature 200 °C tube lens offset voltage 15 V. (Reprinted from Pati et al., 2006, Simultaneous separation and identification of oligomeric procyanidins and anthocyanidins-derived pigments in raw red wine by HPLC-UV-ESI-MSn, Journal of Mass Spectrometry, 41, p. 869, with permission from John Wiley Sons, Ltd.)...

The A-T type polymers gave a more complicated fragmentation pattern and thus appeared to have an additional fragmentation pathway. For instance, A-T type polymers had a tendency to eliminate a mass of 290 instead of 288 for the T-A type polymers. In the case of procyanidins, cleavage of the interflavonoid bond (C4-C8 or C4-C6) gives rise to two types of fragment ions. One is the carbonium ion at the C4 position of the upper procyanidin unit and anodier is a... 

Kiehne et al. [282] who analyzed green tea using a thermospray interface in the positive ionization mode could distinguish fragments originating form upper (T) and lower (B) units of dimeric procyanidins. Cleavage of the interflavanoid bond resulted in a carbenium-ion (T-l) and a neutral fragment from the lower unit which could be protonated under the experimental conditions to form a pseudo molecular ion (B + H+). 

Cooper et al. [18] and Kalili et al. [27] used a UHPLC with a Q-TOF system as the HR-MS and a hybrid system to analyze procyanidins in cocoa samples. By using these systems, higher screening and selectivity was obtained. As is very well known, this hybrid system (Q-TOF) combines the advantages of both different analyzers, and offers a great potential for the screening, selectivity, confirmation, and, above all, the structural elucidation of unknown compounds in complex matrices, such as cocoa samples, due to the mass accuracy of a characteristic fragment ion in studied compounds. 

Fig. 7.7.4. Representative structure of a procyanidin treated with base. R = H or other flavanoid fragments...

---