Bromocresol purple (BCP) or 5′,5″-dibromo-o-cresolsulfophthalein, is a dye of the triphenylmethane family (triarylmethane dyes) and a pH indicator.In its cyclic sulfonate ester form, it has a pKa value of 6.3, and is usually prepared as a 0.04% aqueous solution.