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Abstract: One major drawback of continuous processes is chemical fouling which is typical-ly met by a premixing stage. Within the joint research program KoPPonA 2.0, mixing mechanisms in milli- and micro-systems are investigated phenomenologically in order to better understand the processes that lead to fouling. The current experimental procedures to characterize mixing performance are however limited to the detection of a single tracer or only give a global representation of the mixing performance. This work uses a novel imaging UV-vis spectroscopy developed by Kexel et al.(2021) to locally resolve the 2D concentration fields of a transient reactive multicomponent system. The proposed method expands conventional UV-vis to a spatially (i.e., micrometer scale) and temporally (i.e., millisecond scale) resolved absorbance spectrum in reactive multicomponent systems. In contrast to conventional global UV-vis analytics, discrete parts of the absorbance spectrum are recorded locally within the milli channel on a high-speed CCD camera with telemetric lens. A reactive system (HCl/NaOH) is used to visualize the mixing process in the cascade mixer model 15 by Ehrfeld Mikrotechnik GmbH, manufactured from fused silica glass by means of selective laser-induced chemical etching. The locally resolved 2D concentration field is analyzed to identify regions and operating parameters of insufficient mixing, which are one main cause of polymer fouling. The authors gratefully acknowledge the support by the Federal Ministry for Economic Affairs and Climate Action (BMWK) within the ENPRO 2.0 initiative, project ‘‘Continuous polymerisation in modular, intelligent reactors resistant to the formation of deposits (KoPPonA 2.0); sub-project: CFD modelling of deposit formation processes’’, funding code 03EN2004H.