

Bromophenol blue (3,3,5,5-tetrabromophenolsulfonphthalein, BPB) is used as a pH indicator, a color dye. It is prepared by slowly adding excess bromine to a hot solution of phenolsulfonphthalein in glacial acetic acid. It is also used as a color marker to monitor the DNA or protein agarose gel electrophoresis and polyacrylamide gel electrophoresis.
