A spectrometer device for analysis of aerosol particles, dusts, and other microparticles and/or nanoparticles includes an electrospray ionization source supplying a particle stream to an aerodynamic lens that focuses and collimates a beam of particles. An electrostatic trap accepts the beam of particles and traps a single trapped particle at a time in the electrostatic trap to oscillate with a measurable amplitude and frequency. A sensor senses the amplitude and frequency, and a processor determines a calculated mass to charge ratio from the amplitude and frequency of oscillation of the trapped particle in real time. A method creates a focused stream of micro or nanoparticles, traps a single particle at a time in an electrostatic trap. The amplitude and frequency of the oscillation of the trapped particle is sensed. The mass to charge ratio is determined from the amplitude and frequency of oscillation. Particles can be accelerated into a target.