The ionic liquid 1-ethyl-3-methyl imidazolium tetrafluoroborate (EMI+BF4−) is electrosprayed in a vacuum from positively charged Taylor cones, and the full sprays are analyzed by time of flight mass spectrometry (TOFMS). They contain predominantly the ions (EMI-BF4)nEMI+ (n=0,1,2), at current levels of several μA. Current versus arrival time distributions I(t,L) are measured in a planar disk collector at varying sources to collector distances L, yielding ion-resolved angular current distribution in the polar angle range 21°<θ<37°. Comparison of experimental TOF curves to those expected for the measured angular distribution for a plane collector and a point source shows that the ions are essentially monoenergetic. Hence the present ion source is similar in quality to liquid metal ion sources, while offering a much richer range of chemical composition and mass, including large molecular positive and negative ions. Reinterpretation of the TOF curves as angular distributions shows (indirectly and provisionall...
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