Bromophenol blue is useful as a tracking dye in electrophoresis, an industrial dye, a laboratory acid-base indicator and a biological stain. In gel electrophoresis it can be used as a color marker and as as a biological stain it can be used to stain proteins and nucleic acids. Bromophenol blue is an intermediate and is used as an acid-based indicator in the pH range of 3-4.6 where the color changes from yellow to blue. An electrophoresis tracking dye also used as an acid-base indicator