Table 2.
Retention times, UV, MS, and MS2 data of phenolic acids and flavonols in the onion aqueous extract.
| Peak Number | Compound | tR (min) | UV λmax (nm) | [M + H]+ (m/z) | MS2 (m/z) | [M − H]− (m/z) | MS2 (m/z) |
|---|---|---|---|---|---|---|---|
| 1 | Protocatechuic acid glucoside | 11.1 | 220, 260, 294 | - | - | 315 | 153 (100), 109 (25) |
| 2 | Protocatechuic acid 1 | 13.0 | 220, 260, 294 | - | - | 153 | 109 (100) |
| 3 | Vanillic acid 1 | 23.5 | 218, 260, 294 | - | - | - | - |
| 4 | Quercetin 7,4′-diglucoside 2 | 31.6 | 254, 268sh, 366 | 627 | 465 (100), 303 (89) | 625 | 463 (100), 301 (27), |
| 5 | Quercetin 3,4′-diglucoside 2 | 34.7 | 254, 266, 350 | 627 | 465 (100), 303 (53) | 625 | 463 (100), 301 (14), |
| 6 | Quercetin 3-glucoside 2 | 36.9 | 256, 270sh, 374 | 465 | 303 (100) | 463 | 301 (100), 191 (60) |
| 7 | Ellagic acid 1 | 42.2 | 254, 306sh, 370 | - | - | 301 | - |
| 8 | Quercetin 4′-glucoside 2 | 42.8 | 254, 268sh, 366 | 465 | 303 (100) | 463 | 301 (100) |
| 9 | Isorhamnetin 4′-glucoside 2 | 45.3 | 254, 374 | 479 | 317 (100) | 477 | 315 (100), 300 (20) |
| 10 | Quercetin 1 | 48.9 | 256, 268sh, 370 | 303 | 285 (27), 257 (100), 229 (76), 165 (66), 201 (44), 187 (43) | 301 | 151 (100), 179 (49), 187 (24), 164 (12), 239 (10) |
| 11 | Isorhamnetin 1 | 52.7 | 254, 374 | 317 | 302 (100), 285 (45), 257 (25), 139 (23), 135 (11) | 315 | 300 (100) |
Experimental conditions as described in Material and Methods. 1 Confirmed with reference standard. 2 The glycosylation site was tentatively assigned on the basis of literature data.