The mass spectrometer was operated in positive ion mode. Spray
voltage was set at 4.5 kV. The capillary temperature was set at
250 ◦C. Tube lens and skimmer voltages were set at 50 and 20 V,
respectively. Nitrogen was used as sheath, auxiliary and swee pcone
gas at flow rate of 15, 2 and 1 (arbitrary units), respectively. Heater
temperature was set at 200 ◦C.