B 2102 (OTTO) 5-Bromo-4-chloro-3-indolyl phosphate disodium salt, 98% Cas 102185-33-1 - used to prepare a stock solution that in combination with NBT and a reaction buffer, form a substrate solution for alkaline phosphatase. This substrate system, when incubated with alkaline phosphatase, produces an insoluble NBT diformazan product that is easily observable with its purple color. For added convenience, a mixture of BCIP and NBT is provided in an easily dissolvable tablet form or as a ready-to-use liquid.