Tetrabromophenol Blue is used as acid-base indicator. It is used in oxidative- as well as in non-oxidative hair dye formulations. It is used as an industrial dye, a laboratory indicator, and a biological stain.
Norman M. Stover; Reuben B. Sandin. Use of Boric Acid in Micro-Kjeldahl Determination of Nitrogen. Ind. Eng. Chem. Anal. Ed. 1931, 3, (3), 240-242.
Acid-base indicator: pH 3.0 - 4.6.