Table 1.
Summary of the major ionic fragments of [RF − H]− (m/z 375) observed upon collisional dissociation (CID), higher-collisional dissociation (HCD), gas-phase UV–visible laser photoexcitation, and solution-phase on-line UVA (365 nm) photolysis.
| Ionic Fragment Mass (m/z) 1 | Proposed Structure of Fragment | Mass of Accompanying Neutral Mass Lost | Observed in CID (via H2O) 1,2 | Observed in HCD (via EtOH) | Observed in Laser UV–Visible Photoexcitation 1,2 | Observed via Solution-Phase On-Line UV-A Photolysis 1,2 | ||
|---|---|---|---|---|---|---|---|---|
| 25% | 50% | 3 min | 6 min | |||||
| 255 |
|
120 | (vs) | (s) | (m) | (s) | (w) 4 | (vw) |
| 241 |
|
134 | - | - | (w) | (w) | (w) | (vs) |
| 212 |
|
163 | - | (w) | (m) | (w) | (w) | (w) |
| 145 |
|
230 | - | (w) | (w) | (w) | - | - |
1 Determined with mass accuracy > 0.3 amu. 2 Very strong (vs.), strong (s), medium (m), weak (w), and very weak (vw). 3 Fragment ions with masses above that of the parent ion at m/z 375 stem from that of the RF dimer complex (i.e., [RF − H]− RF at m/z 751) and its photofragment (i.e., at m/z 617). The ion at m/z 617 results from the loss of 134 Da (C5H10O4) from the dimer complex at m/z 751. 4 Notably, the ion at m/z 255 is thought to be produced from deprotonated RF during the ESI process or through in-source dissociation, and is thus intensely observed pre-irradiation.