Single isolated droplets with net charge as a source of ions

A levitation device for charged particles has been used to position a single isolated droplet at a time at atmospheric pressure near the sampling orifice of a vacuum chamber. Following a brief desolvation period (550 ms), a series of coluomb fission events were initiated. Several atmospheric pressure electrode designs were evaluated with respect to guiding the progeny droplets/ions, to the sampling orifice. The best design tested consisted of a series of four annular electrodes of decreasing radius positioned above the levitation ring electrodes, and, on average, 40 ions were counted per single isolated droplet. The ion utilization (charge detected versus charge in the original droplet) with this electrode design has been estimated to be 5 x 10(-6), a substantial improvement over the current utilization measured to be < or = 1 x 10(-9) with a conventional electrospray ion source using the same vacuum apparatus.