## 3 Results and Discussion
### Quantitative Analysis of Identified Metabolites Using HPLC  
From the LC-TOF/MS analysis, the identified major metabolites (**1-8**) from the extract of _E. globulus_ leaves were quantified to evaluate the optimized extraction ratio. As shown in Figure 3, each peak was verified by retention time using an authentic sample. All samples were evaluated as to LOD, LOQ, and linearity (R\({}^{2}\)) by each standard curve with appropriate concentrations (0-200 \(\rm\mu g/mL\)) to confirm their contents in the extracts. As shown in Figure 3 and Table 4, the phenolic contents per 1 g of dried _E. globulus_ leaves were assessed using HPLC at 254 nm. Among the eight metabolites, the most polar compound (salicylic acid \(\beta\)-D-O-glucuronide, **1**) was distributed with 2.77-9.6 mg/g. Chlorogenic acid (**2**) was contained in amounts ranging from 2.83 to 5.90 mg/g in most extracts except for the 0% ethanol extract (0.98 mg/g). Compound **3** (epicatechin) showed the most difference in content when extracted using different ethanol ratios. The content of epicatechin ranged from 98.3 to 142.4 mg/g at a high ratio of ethanol (50-100%). Under the 0-30% ethanol conditions, the contents observed were 0.24-14.64 mg/g. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline \multirow{2}{*}{**No**} & **RT** & **Observed** & **Theoretical** & **Error** & **Formula** & **Identification** \\  & **(min)** & **Mass (\(m/z\))** & **Mass (\(m/z\))** & **(ppm)** & **Formula** & **Identification** \\ \hline
1 & 1.7 & 315.0721 & 315.0716 & +1.59 & C\({}_{13}\)H\({}_{14}\)O\({}_{9}\) & Salicylic acid \(\beta\)-D-O-glucuronide \\
2 & 6.7 & 355.1014 & 355.1029 & +4.22 & C\({}_{16}\)H\({}_{18}\)O\({}_{9}\) & Chlorogenic acid \\
3 & 7.8 & 291.0857 & 291.0869 & \(-4.12\) & C\({}_{15}\)H\({}_{14}\)O\({}_{6}\) & Epicatechin \\
4 & 17.0 & 617.1129 & 617.1143 & \(-2.27\) & C\({}_{28}\)H\({}_{24}\)O\({}_{16}\) & 2\({}^{\prime\prime}\)-O-Galloylhyperin \\
5 & 17.3 & 465.1021 & 465.1033 & \(-2.58\) & C\({}_{21}\)H\({}_{20}\)O\({}_{12}\) & Isoquercitrin \\
6 & 19.3 & 421.1502 & 421.1499 & +0.71 & C\({}_{21}\)H\({}_{20}\)O\({}_{9}\) & Isobarnontin \\
7 & 20.2 & 449.1063 & 449.1084 & \(-4.68\) & C\({}_{21}\)H\({}_{20}\)O\({}_{11}\) & Quercitrin \\
8 & 22.2 & 479.0796 & 479.0826 & \(-6.26\) & C\({}_{21}\)H\({}_{18}\)O\({}_{13}\) & Quercetin-3-O-glucuronide \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Characterization of major metabolites of _E. globulus_ leaf extract. Among the flavonoid contents, 2''-O-galloylhyperin (**4**) occupied the largest proportion and showed contents of 19.7-22.90 mg/g in the presence of ethanol in the extraction conditions. Isoquercitrin (**5**) had the highest content in the 70% ethanol condition with 14.8 mg/g, whereas other conditions were detected at similar levels with 5.26-9.90 mg/g. Isorhapontin (**6**), quercetin (**7**), and quercetin 3-O-glucuronwide (**8**) were quantified at relatively minor levels below 2 mg/g under all the extraction conditions. Overall, the representative eight metabolite (**1-8**) contents were present at high levels in _E. globulus_ leaf extract when the ethanol conditions were more than 50%. However, the radical scavenging effects mentioned above showed the most activity in the 30% ethanol condition. Therefore, the results suggest that the flavonoids rather than the phenolics influenced the _E. globulus_ leaf extracts.