Bromocresol purple
Encyclopedia
Bromocresol Purple or 5',5"-dibromo-o-cresolsulfophthalein, is a pH indicator
PH indicator
A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions or hydrogen ions in the Arrhenius model. Normally, the indicator causes the...

. The most common solution is 0.04% aqueous.

Uses

Besides its primary function as an indicator, Bromocresol Purple is used in medical laboratories to measure albumin
Albumin
Albumin refers generally to any protein that is water soluble, which is moderately soluble in concentrated salt solutions, and experiences heat denaturation. They are commonly found in blood plasma, and are unique to other blood proteins in that they are not glycosylated...

, and as an addition to acid stop baths used in photographic processing as an indicator that the bath has reached neutral pH and needs to be replaced.
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