Catechin 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]. 

Precursors. The precursors for this reaction are anthocyanins, flavanols or flavanols containing a vinyl residue at C-8 (i.e., 8-vinylflavanols). 8-Vinylflavanols could arise from the cleavage of flavanol-ethyl-flavanol oligomers or from the dehydration of the flavanol-ethanol adduct formed after the attack of aldehyde cation to the flavanol (Chapter 9B). Saucier et al. (1997) have supported evidence for this precursor when detecting an ion corresponding to vinyl-catechin from the fragmentation of ethyl-linked catechin dimers under ESI-MS in positive or negative mode. 

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. 

Scheme 6 Major fragmentations of protonated catechin. The insert gives the ion nomenciature for protonated fiavan-3-ois. (From Ref. 35.)...

The most useful fragmentations in terms of eharacterization of the methylation or metabolism sites of catechin are those resulting in stmeturally informative and ions. Indeed, the study of the different mass shifts of the three diagnostic ions observed between catechin and its methylated analogues... 

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