UV/VIS detection is one of the most sensitive detection techniques in trace-level chromatography. Sometimes, however, spectrophotometric detection lacks sensitivity, selectivity or reproducibility and chemical derivatizations are required. By using Metrohm`s rugged and versatile flow-through reactor, single- or multi-step derivatizations can be done fully automatically, in either pre- or post-column mode at any temperature between 25…120 °C. The variable reactor geometry allows to adjust the reactor residence time of the reactants according to derivatization kinetics. The flexibility of the reactor is demonstrated by optimizing four widespread post-column techniques: the relatively slow ninhydrin reaction with amino acids and the fast derivatizations of silicate, bromate and chromate(VI).