We are developing aerosol generating and processing methods for X-ray analyses of nanoscale materials using conventional synchrotron radiation sources and using the newly operational soft X-ray free-electron laser in Hamburg (FLASH) at the Deutsches Elektronen Synchrotron. Charge-reduced electrospray, differential mobility analysis and an electrostatic precipitator were used to prepare samples consisting of size-monodisperse spherical nanoparticles deposited on 20 nm thick silicon nitride foils supported by silicon frames. Ninety-seven and 102 nm diameter spheres were selected from a broader distribution of 98 nm spheres using differential mobility. We measured the size distribution of the spheres using forward scattering from 1.65 nm light at the Advanced Light Source (ALS) in Lawrence Berkeley National Laboratory and scanning electron microscopy (SEM). The full-width half maximum (FWHM) of the size distribution of the size-selected spheres was as narrow as 5.4nm when measured by SEM, as compared to 16 nm for the non-size-selected distribution. Forward scattering measurements of the 97 nm diameter size-selected spheres fit a size distribution with a FWHM of 4 nm and allowed us to validate the methodology for use in future diffraction imaging experiments at FLASH. (C) 2007 Elsevier Ltd. All rights reserved.