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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 2116 (OTTO) Bromocresol purple, solution Cas 115-40-2 - used in medical laboratories to measure albumin.