Fast Blue B Salt is a stain that is used for the determination of various compounds. It has been used to demonstrate esterase activity. Histochemically it has stained enterochromaffin cells and cells that have gone under free radical oxidative damage. It can be used as reactant/reagent in one pot preparation of phenanthroline-based shape-persistent fluorescent macrocycle using Sonogashira coupling. Dyes and metabolites.