The interest in nano particles from the view of basic and applied research has constantly risen in recent years. Since their physical properties are different from those of bulk materials, new industrial applications are emerging, e.g. in microelectronics. For quality control, particle production technologies call for on-line techniques that respond to the chemical nature of the particles. A particle generation process usually leads to particles with different surface properties. These surface properties, i.e. impurities ( like an oxygen layer ) or the crystal habit of single particles, determines much of their behaviour, especially in the diameter range of a few nanometers. While this fact has hardly been recognized, we anticipate that new technologies will establish a demand not only for analysis but also for separation of chemically pure particles with respect to their surface properties. In these PHD thesis we introduce a method and a device to separate aerosol particles according to their photoelectric properties. These strongly depend on particle surface composition as well as the particle morphology.