In connection with the development of a complete screening setup for organometallic catalysis, a micromixer-tube setup was investigated to optimize its serial transient operation mode. Because homogeneously dissolved catalysts and substrates in the liquid phase of a gas/liquid system are pulse-injected into the two-phase system, our investigations aim in finding a minimum in the signal broadening and maximizing the number of experiments per unit of time. Within this context, investigations of the residence time distribution of the whole setup, as well as the individual contributions of its respective components toward signal broadening, were undertaken by determining the effects on the residence time distribution by the gas/liquid ratio, the orientation of the residence time loop and the total flow rate. (C) 2004 American Institute of Chemical Engineers.