A hybrid setup consisting of low pressure burner, flow reactor and photo-ionization mass spectrometer was used for the simultaneous detection of primary soot and of flame generated nanoparticles precursing soot. The studied flames were low pressure (120-180 mbar) C2H4/O2 flames surrounded by an N2 shield. The flow reactor was not used in this study. Through variation of the burner conditions (stoichiometry, sampling height) it could be shown that nanoparticles and soot are entirely independent species. The former, in particular, are found very early in the flame and their concentration profiles do not vary very much throughout the flame. This renders the possibility that nanoparticles are emitted together with soot and consequently may constitute an additional environmental hazard. Photo-ionization mass spectrometry is well suited for the detection of these particles.