Table I.
Theoretical and Observed Mass Values for Unabled and 13C Isotope-Labled Citric acid and Glycine Used in Photochemical Degradation Studies and Observed Mass Values for the Reaction Products
| Citric Acid (Isotope) | MW (Theor.) | Glycine (Isotope) | MW (Theor.) | DNPH-AC [M-H]− | Gly-AC [M+H]+ (Obs.) | Gly-AC MS2 [M+H]+ (Obs.) | Gly-AC MS3 [M+H]+ (Obs.) |
|---|---|---|---|---|---|---|---|
| 13C6 | 198.05 | 12C2 | 75.04 | 240.17 | 135.08 | 89.08 | 60.08 |
| 2,4-13C2 | 194.03 | 12C2 | 75.04 | 239.17 | 134.08 | 88.08 | 60.08 |
| 1,5-13C2 | 194.03 | 12C2 | 75.04 | 237.17 | 132.08 | 86.08 | 58.08 |
| 12C6 | 192.03 | 12C2 | 75.04 | 237.17 | 132.08 | 86.08 | 58.08 |
| 12C6 | 192.03 | 13C2 | 77.05 | NA | 134.08 | 87.08 | 59.08 |
| 12C6 | 192.03 | 2-13C | 76.05 | 133.08 | 87.08 | 59.08 | |
| 12C6/13C6 | 192.03, 198.05 | 12C2 | 75.04 | 132.08, 135.08 | 86.08, 89.08 | 58.08, 60.08 | |
| 12C6/2,4-13C2 | 192.03, 194.03 | 12C2 | 75.04 | 132.08, 134.08 | 86.08, 88.08 | 58.08, 60.08 |
The DNPH-acetone hydrazone (DNPH-AC) observed [M-H]1− m/z are shown as well as the [M+H]1+ m/z for acetone modified glycine (Gly-AC) and the corresponding products ions observed in CID-MS2/MS3 scans. The chemical structures of citrate, glycine, glycine-acetone, the corresponding glycine-acetone product ions and the labeled carbons associated with the structures are shown below the table.