Description_x000D_ Application_x000D_ Fast blue RR salt has been used in the immunohistochemistry to detect the activity of alkaline phosphatase. It has been used in the procedure of connective tissue staining using picrosirius red._x000D_ Packaging_x000D_ 25 g in glass bottle_x000D_ Biochem/physiol Actions_x000D_ Fast blue RR is mainly used in histological stainings. It binds to the reaction product of alkaline phosphatase and precipitates it as an insoluble compound. The sites of alkaline phosphatase activity appears black. Fast blue RR is also used for the detection of esterase activity. It couples with naphthol (released from naphthol acetate) and forms an insoluble azo-dye which appears red/blue.