Merck, P4272-25G, 3-(2-Pyridyl)-5,6-di(2-furyl)-1,2,4-triazine-5′,5′′-disulfonic acid disodium salt

3-(2-Pyridyl)-5,6-di(2-furyl)-1,2,4-triazine-5′,5′′-disulfonic acid disodium salt, also known as Ferene, is commonly used to measure the concentration of iron ions in aqueous solutions. The reagent is sensitive to ferrous iron ions (Fe2+) and forms a purple-colored complex with these ions in the presence of a reducing agent. The intensity of the purple color formed is proportional to the concentration of iron ions present in a solution and is quantified spectrophotometrically.