Mass spectrometry. The mass spectrum resulting from the UV multiphoton dis- sociative ionization of phenanthridine is shown in Fig. 2A. Mass peaks are observed at m/z = 180, 179, 152, 151 and 150. The peak at m/z = 179 is attributed to the phenanthridine radical cation. The intense peak at m/z = 180 is likely due to protonated phenanthridine that is formed by a self-protonation reaction of the radical cation Phe●+ with neutral phenanthridine present as a background vapor:37 Published on 22 December 2016. Downloaded by Radboud University Nijmegen on 4/8/2019 9:07:29 AM. Phe●+ + Phe - H+Phe + [Phe–H]● (1) The very weak signal observed at m/z = 153 corresponds to C2H2-loss from phenanthridine and contains a contribution of the 13C component of the product at m/z = 152. The mass peak observed at m/z = 152 is clearly more intense and corresponds primarily to the HCN-loss channel: C13H9N●+ - C12H8●+ + HCN (2) This signal also possibly contains a small contribution of a product formed through C2H2-loss accompanied by dehydrogena- tion, as was observed in high mass resolution experiments.27 Mass peaks at m/z = 151 and 150 represent (further) dehydrogena- tion of products formed from HCN- and/or C2H2-loss. The middle trace in Fig. 2 shows the normalized mass spectrum that is recorded after applying the SWIFT-pulse to the repeller endcap of the ion trap. SWIFT excitation results in a clean isolation of the product at m/z = 152, with only a small fraction of the initial (protonated) phenanthridine left in the trap. Finally, the bottom trace in Fig. 2 shows the normalized mass spectrum that is obtained when XXXXX is tuned to 750 cm—1, which is resonant with a vibrational transition in the m/z = 152 fragment. Fragments induced by IRMPD are detected at m/z = 151 and 150 corresponding to H- and H2-loss. Mass spectra recorded for dissociative ionization of acridine result the same fragments and isolation is achieved in a similar fashion. The effect of the trapping time on the ion signal intensities is investigated and discussed in detail in Fig. S2 of the ESI.†
Mass spectrometry. Mass spectra were recorded using a micromass ZQ 2000 instrument (Waters, UK), operating in negative electrospray ionisation (ESI) mode. The sample was directly infused into the ESI source at a 20 μl/ min flow rate. The nebulization gas was N2, the capillary potential was 2.80 kV, the drying gas was 500 l/ h and the RF lens was set to – 0.5 V. The sample cone voltage was set to -40 V and the source temperature was 100 °C whilst the desolvation temperature was set to 250 °C. The sample concentration was 100 µg/ mL, prepared in 50% methanol, 50% water and 0.1% FA.
