[en] A new setup named Fast On-line Reaction Apparatus (FORA) is presented which allows for the efficient investigation and optimization of metal carbonyl complex (MCC) formation reactions under various reaction conditions. The setup contains a ${}^{252}$Cf-source producing short-lived Mo, Tc, Ru and Rh isotopes at a rate of a few atoms per second by its 3% spontaneous fission decay branch. Those atoms are transformed within FORA in-situ into volatile metal carbonyl complexes (MCCs) by using CO-containing carrier gases. Here, the design, operation and performance of FORA is discussed, revealing it as a suitable setup for performing single-atom chemistry studies. The influence of various gas-additives, such as CO${}_2$, CH${}_4$, H${}_2$, Ar, O${}_2$, H${}_2$O and ambient air, on the formation and transport of MCCs was investigated. O${}_2$, H${}_2$O and air were found to harm the formation and transport of MCCs in FORA, with H${}_2$O being the most severe. An exception is Tc, for which about 130 ppmv of H${}_2$O caused an increased production and transport of volatile compounds. The other gas-additives were not influencing the formation and transport efficiency of MCCs. Using an older setup called Miss Piggy based on a similar working principle as FORA, it was additionally investigated if gas-additives are mostly affecting the formation or only the transport stability of MCCs. It was found that mostly formation is impacted, as MCCs appear to be much less sensitive to reacting with gasadditives in comparison to the bare Mo, Tc, Ru and Rh atoms.