End-on inductively coupled plasma optical emission spectrometry (ICP-OES) of the relative mass distributions in ensembles of spherical SiO₂ particles with small and large size variations is presented. The particles are introduced into the ICP by injection of monodisperse microdroplets generated from diluted particle suspensions. The spectroscopic signals, taking into account the peak or the integrated intensities of the Si 288.16 nm line, are compared with mass distribution measurements of corresponding SiO₂ particle ensembles performed by Scanning Electron Microscopy (SEM). It is found that the relative mass distributions measured by ICP-OES are in good agreement with SEM measurements if the spectroscopic signal to noise ratio is sufficiently large indicating that intensity variations due to different particle trajectories in the ICP are less important than expected.