Trapping charged nanoparticles in the nano aerosol mass spectrometer (NAMS)

Abstract

Particle trapping in the nano aerosol mass spectrometer (NAMS) is investigated through a combination of modeling and experimental measurements to understand and optimize the trapping process. In the NAMS, charged nanoparticles pass through an aerodynamic lens, digital ion guide (DIG) and field adjusting lens (FAL) prior to entering a digital ion trap (DIT) where they are captured and subsequently analyzed. The DIT is operated with a square wave potential applied to the ring electrode. SIMION modeling was used to study particle motion from the exit aperture of the DIG into the DIT. Several parameters were characterized including particle starting position, kinetic energy, trajectory and FAL design. A new FAL assembly was designed to increase the number of trapped particles. The new design was found to increase the rate that ambient particles are analyzed by over an order of magnitude. With the new design, an ambient aerosol concentration (d N/dlog d m) of 1 × 10 3 cm −3 yields approximately 2–3 particles analyzed per minute.