Radial Differential Mobility Analyzer for One Nanometer Particle Classification

We present details on the design, construction, and calibration of a radial differential mobility analyzer suitable for sizing aerosol nanoparticles with mobility diameters as small as one nanometer. Design improvements targeted decreasing the residence time with a concomitant reduction in particle agglomeration and diffusional losses to walls. Calibration was performed using aerosolized monodisperse molecular ions. Instrument resolution was found to increase with applied voltage as V 1/2 , indicating that diffusion is broadening the transfer function and reaching a value of ∼7 for the largest molecular ion measured (mobility diameter of 1.47 nm). The mobilities of three molecular ions in the tetra-alkyl ammonium halide homologous series are also reported.