Table 1. Amino acid abundance.
Summary of the average amino acid abundance (micromolar) of the blank-corrected 6 M HCl acid-hydrolyzed reaction product solution from the hydrothermal experiment containing ammonia, formaldehyde, and glycolaldehyde heated at each temperature for 72 hours and analyzed by HPLC and UPLC-FD/QToF-MS. Quantification of the amino acids included background-level corrections using a control sample treated under the same experimental conditions without the presence of ammonia. The associated errors are SDs. The amino acid solutions were derivatized by ο-phthaldialdehyde (OPA)/N-acetyl-l-cysteine (NAC) derivatization (15 min for UPLC/QToF-MS and in-line for HPLC) and identified by comparison to the retention time of the amino acid standard run on the same day. The abundance (micromolar) of each amino acid was acquired by the peak area integration of the corresponding representative mass/charge ratio (m/z). 2nd, second run of the hydrothermal experiments; 3rd, third run of the hydrothermal experiments; free, amino acid analyses conducted without acid hydrolysis. Enantiomers could not be separated under the present chromatographic conditions for β-AIB and α-ABA. Asp, aspartic acid; Glu, glutamic acid; Ser, serine; Thr, threonine; Gly, glycine; Ala, alanine; Iva, isovaline; Val, valine; n.d., not detected.
| Peak no. | Amino acid | Concentration in micromolar | |||||||
| HPLC | UPLC/QToF-MS | ||||||||
| 90°C | 150°C | 150°C 2nd | 150°C free | 150°C 2nd (free) | 200°C | 250°C | 150°C 3rd | ||
| 1 | d-Asp | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | <3.4 |
| 2 | l-Asp | 2.6 ± 0.3 | |||||||
| 3 | l-Glu | 58 | 24 | 33 | n.d. | n.d. | 8–14 | 12.3 | 9 ± 3.4 |
| 4 | d-Glu | 11.8 ± 0.6 | |||||||
| 5 | d-Ser | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | 2.5 ± 0.3 |
| 6 | l-Ser | <0.1 | |||||||
| 7 | d-Thr | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | <0.1 |
| 8 | l-Thr | <0.1 | |||||||
| 9 | Gly | 249 | 331 | 278 | 31 | 22 | 272–308 | 53.0 | 344.1 ± 11 |
| 10 | β-Ala | 199 | 171 | 187 | 40 | 30 | 38–42 | n.d. | 218.9 ± 6.3 |
| 11 | d-Ala | 495 | 479 | 534 | 247 | 182 | 687–759 | n.d. | 635.8 ± 13 |
| 12 | l-Ala | 444.8 ± 11.6 | |||||||
| 13 | γ-ABA | 16 | 31 | 48 | n.d. | 2 | 132–143 | 133.3 | 53.4 ± 9.9 |
| 14 | d,l-β-AIB | 19 | 6 | 9 | n.d. | n.d. | n.d. | n.d. | <0.1 |
| 15 | d-β-ABA | 13.1 ± 0.3 | |||||||
| 16 | l-β-ABA | 13.4 ± 0 | |||||||
| 17 | α-AIB | 3.9 ± 0.1 | |||||||
| 18 | d,l-α-ABA | 78 | 100 | 53 | n.d. | n.d. | 140–191 | n.d. | 38.2 ± 3.2 |
| 19 | d-Iva | <0.1 | |||||||
| 20 | l-Iva | <0.1 | |||||||
| 21 | l-Val | n.d. | n.d. | n.d. | n.d. | n.d. | 35–64 | n.d. | <10.9 |
| 22 | d-Val | <1.0 | |||||||
| Total | 1115 | 1141 | 1142 | 319 | 235 | 1313–1521 | 199 | 1792 | |