o-Diamines as reagents for selenium : Part I. 4-dimethylamino-1,2-phenylenediamine

4-Dimethylamino-1,2-phenylenediamine is investigated as a photometric and qualitative reagent for selenium. With this reagent selenium (IV) forms 5-dimethylamino-2,1,3-benzoselenadiazole, a red colored compound, with an absorption maximum in the visible region at 500 mμ. Variables such as reagent stability, extinction stability, reaction rate, influence of acidity, foreign ions, validity of Beer's law are discussed. The reagent is highly selective for selenium, has good sensitivity and recproducibility, and is also useful for qualitative purposes.