Bromophenol Blue, sodium salt

Bromophenol blue (3',3'',5',5''-tetrabromophenolsulfonphthalein) is used as a pH indicator, a color marker, and a dye. As an acid-base indicator, its useful range lies between pH 3.0 and 4.6. It changes from yellow at pH 3.0 to blue 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 a 1X TAE buffer or TBE buffer, bromophenol blue migrates at the same rate as a DNA fragment of about 300 base pairs, in 2% agarose as 150 bp.