Flame spray pyrolysis is an important method of nanoparticle manufacturing. Reactions of the precursor and the solvent determine which intermediates can contribute to particle formation. To investigate the chemical interaction between the solvent and the precursor during the partial evaporation of the spray preceding ignition, precursor solutions were sprayed into an externally heated flow reactor. The thermal decomposition of the precursors Fe(CO)(5), Fe(C5H5)(2), and Ti(i-OC3H7)(4) in solutions of xylene and ethanol was investigated. Decomposition products were analyzed by mass spectrometry. The relevance of reactions at these low temperatures for the spray-flame process is substantiated by measurements of the spatial temperature distribution of the spray flame. Depending on the relative thermal stabilities of the precursor and the solvent, the less stable component can initiate decomposition of the more stable component, resulting in different reaction patterns of the solutions. The results are discussed with regard to their potential influence on particle formation pathways.