Bromocresol purple (BCP) or 5',5"-dibromo-o-cresolsulfophthalein, is a pH indicator. In its sultone form, it has a pKa value of 6.3, and is usually prepared as a 0.04% aqueous solution.
B 2115 (OTTO) Bromo cresol purple, GR Cas 115-40-2 - used in medical laboratories to measure albumin. In microbiology, it is used for staining dead cells based on their acidity, and for the isolation and assaying of lactic acid bacteria.