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.
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.†
