Investigation of electrospray ionization and electrostatic focusing devices using a three-dimensional electrospray current density profiler.

A novel instrument for profiling the current density of nanoelectrospray ionization plumes in three dimensions has been developed. A hemispherically-shaped electrostatic lens at atmospheric pressure is found to be able to compress the space-charge in nano-ESI and increase the average current density in the plume to three times the nominal value. Ion transmission into a single-quadrupole mass spectrometer is found to roughly double using the electrostatic lens. Data also suggest that ion transmission into the first vacuum region for a skimmer-type mass spectrometer interface using nano-ESI may be typically 40% or better with no special focusing device used.