This study deals with the determination of the relative abundance of the oxide layer in the near-surface volume of aluminum nanoparticles of 50-100 nm in diameter. They are bombarded with a sequence of single projectiles of Au 400(4+) accelerated to 136 keV. The ionized ejecta from each impact are recorded individually which allows identification of ions emitted from a surface volume of approximately 10 nm in diameter and 5-10 nm in depth. The mode of analyzing ejecta individually from each single cluster impact is a means to apply mass spectrometry in nanovolumes.