Effect of liquid properties on electrosprays from externally wetted ionic liquid ion sources

Ionic liquid ion sources (ILISs) are externally wetted and electrochemically etched and sharpened tungsten tips used as electrospraying sources for ionic liquids in a vacuum. They have recently shown an ability to operate as emitters of pure ion beams (no drops), even with ionic liquids of moderate surface tension (gamma < 40 dyn/cm) and electrical conductivity (K < 1 S/m) that had in all prior reports (all based on conventional internally fed capillary tips) always operated in the mixed ion-drop regime. The present study uses time of flight mass spectrometry to analyze full ion beams emitted from ILISs for a diversity of ionic liquids with properties in the wide range 0.26 < K (S/m)< 2.8, 39.3 <gamma (dyn/cm)< 48.6. Remarkably, all liquids tested achieve the purely ionic regime. The main effect of reducing electrical conductivity is a reduction of the emission current from 180 to 10 nA.(C) 2007 American Institute of Physics.