Retarding potential and induction charge detectors in tandem for measuring the charge and mass of nanodroplets.

The determination of the mass of a nanoparticle via time-of-flight typically requires a direct measurement of its charge. This can be done with a differential retarding potential analyzer and an induction charge detector operating in tandem. The spectrometer described in this article selects a particle with a specified retarding potential from a beam and directs it to an induction charge detector where both its velocity and charge are measured. The retarding potential, velocity, and charge also yield the particle's mass. The particle is analyzed without the need to collect it, and therefore can be employed in a subsequent experiment. The high charge sensitivity of the induction charge detector and the capability for working at low retarding potentials make the characterization of electrosprayed nanodroplets possible for the first time.