Methods for Non-Destructive, High Precision Mass/Charge Determination for Single, Trapped, GigaDalton Nanoparticles

Several methods for non-destructive mass measurements on single, trapped nanoparticles in the megadalton(MDa) to gigadalton (GDa) mass ranges are demonstrated, and the trade-offs between speed, precision, and ease of use are discussed. Charged nanoparticles are introduced into vacuum by electrospray ionization, and trapped in a quadrupole ion (Paul) trap, with detection by light scattering. Four different methods for measuring the mass/charge ratios of trapped particles are discussed, all based on measuring the secular frequency for motion of the particle in the trap, working in either the time or frequency domains. The charge is then measured by driving single electron charge changes using either a discharge or vacuum ultraviolet lamp. Several related topics such as the effects of pressure on secular resonance width and the spectrum of simultaneously trapped particles are also discussed.