Quantity Contains 10 mg substrate per tablet. Specificity Nitro Blue Tetrazolium is used in conjunction with the alkaline phosphatase substrate 5-Bromo-4-Chloro-3-Indolyl Phosphate (BCIP) Tablets (Sigma Product No. B0274) in immunoblotting and immunohistological staining procedures. This substrate system produces an insoluble end product that is blue-purple in color and can be observed visually.