Composition, shape and stability of clusters, complexes and ultra small particles play an important role in understanding the mechanisms of particle formation and growth. Ion Mobility Spectrometry – Mass Spectrometry (IMS-MS) offers a method to identify chemical composition and stability (MS) and reveals at the same time information on structure and weakly bonded ligands from the mobility analysis (IMS). The unique installed combination of a back-side scanned high resolution planar differential mobility analyzer (DMA) and ultra high resolution Qq-time of flight (ToF) mass spectrometer allows the investigation of liquid systems by electrospray ionization as well as direct sampling from the gas phase for the investigation of gas phase ion clusters and aerosols.