Bromophenol blue

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Bromophenol Blue

Bromophenol blue (pH indicator)
below pH 3.0		above pH 4.6
3.0	↔	4.6

Bromophenol blue, Tetrabromophenolsulfonephthalein, is an acid-base indicator whose useful range as an indicator lies between pH 3.0 and 4.6. It changes from yellow at pH 3.0 to purple at pH 4.6; this reaction is reversible.

Bromophenol blue is also used as a color marker to monitor the process of agarose gel electrophoresis and polyacrylamide gel electrophoresis. Since bromophenol blue carries a slight negative charge at moderate pH, it will migrate in the same direction as DNA or protein in a gel; the rate at which it migrates varies according to gel density and buffer composition, but in a typical 1% agarose gel in TAE buffer or TBE buffer, bromophenol blue migrates at the same rate as a DNA fragment of approximately 500 base pairs. Xylene cyanol and Orange G may also be used for this purpose.

The molecular weight of bromophenol blue is around 670 Daltons or grams per mole.

The bromophenol blue is also used as a dye. When light is passed through it, it will absorb the rest of the light except red, so only the red light is visible.