In this work, a method of combinatorial variation of reactant solutions combined with an in situ UV-Vis readout of the plasmonic properties during the wet-chemical synthesis of Ag nanoprisms in micro fluid segments is presented. Segment sequences of clearly distinguishable compositions are generated by an automated flow rate program. By the help of two combined slowly shifting and two contrariwise rapidly changing reactant flow rates, a two dimensional parameter space is covered completely in steps of 20 %. Due to the sensitive main dipole mode of Ag nanoprisms, a combinatorial concentration variation during the growth step of the synthesis opens new possibilities regarding tuning of particle size and optical properties. Here, within one combinatorial synthesis run, silver nanoprisms with edge length between 35 and 200 nm and main plasmon resonances between 550 and 900 nm were obtained.