## 3 Results and Discussion
### Mapping Hazelnut Metabolome by Chromatographic Fingerprinting
(**A**) The distribution of 80 targeted 2D peaks (green circles). (**B**) The distribution of untargeted and targeted (UT) peaks (red and green circles) comprehensively covering the chromatographic space. (**C**) The enlarged area highlights the retention region of monosaccharides while illustrating the chromatographic efficiency and resolution achieved by adopting a 60 m \(\times\) 0.25 mm d\({}_{\rm c}\) column in the \({}^{1}\)D. (**D**) For untargeted peak #207, the available metadata including retention times, qualifiers/quantifiers ions, and results of cross-matching by untargeted and targeted (UT) fingerprinting. _Appl. Sci._**2021**, _11_, 525 \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Chemical Class** & **Compound Name** & \({}^{1}\)_t_R_ **(min)** & \({}^{2}\)_t_R_ **(sec)** & **Experimental \({I}^{T}\)** & **Reference \({I}^{T}\)** \\ \hline \multirow{9}{*}{Amino acids} & Alanine 2 TMS \({}^{\text{a,b}}\) & 17.9 & 0.6 & 1098 & 1110 \\  & Leucine TMS \({}^{\text{a,b}}\) & 20.6 & 0.8 & 1151 & 1155 \\  & Isoleucine TMS \({}^{\text{a,b}}\) & 21.6 & 1.1 & 1173 & 1178 \\  & Valine 2 TMS \({}^{\text{a,b}}\) & 23.5 & 0.7 & 1210 & 1208 \\  & Theronine 2 TMS & 27.4 & 0.7 & 1286 & 1292 \\  & Proline 2 TMS \({}^{\text{a,b}}\) & 27.6 & 0.8 & 1289 & 1282 \\  & Glycine 3 TMS \({}^{\text{a,b}}\) & 28.3 & 0.7 & 1302 & 1310 \\  & Threonine 3 TMS & 32.3 & 0.8 & 1380 & 1367 \\  & Aspartic acid 2 TMS \({}^{\text{b}}\) & 34.2 & 1.1 & 1419 & 1413 \\  & 5-Oxoproline 2 TMS & 38.9 & 1.3 & 1516 & 1520 \\  & Aspartic acid 3 TMS \({}^{\text{b}}\) & 39.4 & 0.8 & 1527 & 1522 \\  & Pyroglutamic acid 2 TMS \({}^{\text{a}}\) & 39.4 & 1.1 & 1527 & 1521 \\  &henylalanine TMS \({}^{\text{a,b}}\) & 40.7 & 0.8 & 1555 & 1559 \\  & Ornithineine 3 TMS \({}^{\text{a}}\) & 42.6 & 1.1 & 1607 & 1610 \\  & Glutamic acid 3 TMS \({}^{\text{a}}\) & 43.2 & 1.0 & 1612 & 1626 \\ \hline \multirow{9}{*}{Organic acids} & Lactic Acid 2 TMS \({}^{\text{a,c}}\) & 15.9 & 0.6 & 1051 & 1057 \\  & Glycolic acid 2 TMS \({}^{\text{a}}\) & 16.6 & 0.7 & 1068 & 1072 \\  & Oxalic acid 2 TMS \({}^{\text{a,c}}\) & 19.2 & 0.9 & 1123 & 1125 \\  & Malonic acid 2 TMS & 22.9 & 0.9 & 1197 & 1205 \\  & Benzoic Acid TMS \({}^{\text{a}}\) & 25.3 & 1.2 & 1244 & 1248 \\  & Succinic acid 2 TMS \({}^{\text{a}}\) & 28.6 & 1.0 & 1308 & 1313 \\  & Fumaric acid 2 TMS \({}^{\text{a}}\) & 30.5 & 0.9 & 1345 & 1348 \\  & Decanoic acid TMS \({}^{\text{a}}\) & 36.0 & 0.9 & 1455 & 1450 \\  & Malic acid 3 TMS \({}^{\text{a,c}}\) & 37.4 & 0.9 & 1483 & 1480 \\  & Hexanedioic acid 2 TMS & 38.2 & 1.0 & 1500 & 1498 \\  & Dodecanoic acid TMS & 44.5 & 0.8 & 1648 & 1650 \\  & Azelatic acid 2 TMS & 50.3 & 1.1 & 1789 & 1793 \\  & Citric acid 4 TMS \({}^{\text{a,c}}\) & 51.1 & 0.9 & 1811 & 1816 \\  & Myristic acid TMS & 52.2 & 1.0 & 1844 & 1840 \\  & 3-Deoxyhexonic acid 4 TMS & 52.6 & 0.8 & 1854 & 1855 \\  & Pentadecanoic acid TMS & 55.7 & 1.0 & 1943 & 1943 \\  & Gluconic acid 6 TMS \({}^{\text{a}}\) & 57.4 & 0.8 & 1995 & 1997 \\  & Palmittic acid TMS & 58.9 & 1.1 & 2041 & 2041 \\  & 3-Deoxyarabino-hexaric acid 5 TMS & 60.8 & 0.9 & 2100 & 2092 \\  & (Z,Z)-9,12-Octadecadienoic acid TMS & 64.0 & 1.2 & 2206 & 2208 \\  & (Z)-9-Octadecenoic acid TMS & 64.2 & 1.2 & 2212 & 2215 \\  & (E)-9-Octadecenoic acid TMS & 64.3 & 1.2 & 2218 & 2217 \\  & Stearic acid TMS & 64.9 & 1.1 & 2238 & 2239 \\  & Arachidic acid 3 TMS & 70.2 & 1.0 & 2428 & 2432 \\ \hline \multirow{9}{*}{Polyols} & Glycerol 3 TMS \({}^{\text{a}}\) & 26.5 & 0.6 & 1268 & 1266 \\  & Erythrhitol 4 TMS \({}^{\text{a}}\) & 38.0 & 0.7 & 1496 & 1505 \\  & Xylitol 5 TMS \({}^{\text{a}}\) & 47.4 & 0.7 & 1715 & 1710 \\  & Pinitol 5 TMS & 51.6 & 0.7 & 1827 & 1826 \\  & Scyllo-inositol 6 TMS \({}^{\text{a}}\) & 56.0 & 0.7 & 1952 & 1972 \\  & Myo-inositol 6 TMS \({}^{\text{a,c}}\) & 60.4 & 0.8 & 2087 & 2096 \\  & 1-Monooleoylglycerol 2 TMS & 78.3 & 1.2 & 2752 & 2759 \\ \hline \hline \end{tabular}
\end{table}