FIG. 8.

Influence of the ion source nozzle size on the vacuum chamber pressure during electrospray. (a) Scanning electron micrographs of capillary tips with (a) 4.3 μm outer diameter and 2.9 μm inner diameter and (b) 350 nm outer diameter and 190 nm inner diameter. (c) and (d) show traces of the chamber pressure (black, left axis) and the electrospray current from the tip (gray, right axis) as functions of time for the tips in panels (a) and (b), respectively. Both tips contained 1M NaI in formamide. The total applied extraction voltages were 1.15 kV in (c) and 0.248 kV in (d). The shaded regions indicate times when the safe operating pressure was exceeded and the mass filter and detector turned off.