Argon gas flooding was in operation in order to aid charge compensation, pressure in the main chamber was maintained at 9.0 × 10 -7 bar. The spectra were collected in positive polarity, in mass range m/z 75-1125. The injection time was set to 500 ms and each area analysed lasted 1000 scans, the total ion dose per measurement was 2.62 × 10 14 ions/cm 2 . Mass-resolving power was set to 240,000 at m/z 200.