Fig. 5. Recoveries for the seven-catechin derivatives using three different extraction
procedures. Recoveries were determined with the UHPLC–MS/MS method
presented in Fig. 8A.
obtain a better evidence about the presence or absence of catechin
derivatives. Various generic, simple liquid–liquid extraction
(LLE) procedures were evaluated prior to the UHPLC–UV analysis.
After maceration of tea in pure water, LLE with butanol, ether, ethyl
acetate. . ., were performed according to the literature [5,44,45].
These procedures were compared in term of recoveries, calculated
as the ratio of catechin content in organic solvent and total
catechin content in both water and organic solvent, for the seven
investigated catechins. The recovery values were obtained with the
selective and sensitive UHPLC–MS/MSmethod described in Section
3.3. Fig. 5 shows the results obtained for all catechins using the
three different extracting solvents. Firstly, ether is too nonpolar for
extracting catechins, and it was rejected because all catechins were
recovered in the aqueous phase. The results for ethyl acetate or
butanol were very close with recoveries between 93.7% and 100%
for ethyl acetate and 92% and 100% for butanol. Only the recoveries
of CG and GCG were below these values with both solvents.
The lower values observed for these compounds were attributed to
their rather low concentration in real tea samples, which are below
the limit of quantitation (LOQ). This can make the determination of
these compounds in both phases inaccurate and imprecise.
Considering these observations, ethyl acetate was selected as
the extraction solvent, because it was easier to use than butanol,
which can lead to mixing of the two phases. The two chromatograms
presented in Fig. 6 correspond to the direct injection
of a commercial tea extract infused for 5min (light chromatogram)
and the organic fraction of the same extract after a liquid–liquid
extraction with ethyl acetate (bold chromatogram). This separation