Bromophenol Blue is a pH indicator (pH 3.4 yellow - 4.6 purple) and a tracking dye for nucleic acid or protein electrophoresis in agarose or polyacrylamide gels. Due to the slightly negative charge, the dye will migrate to the anode during electrophoresis, which allows monitoring of the movement of the molecules through the gel. Bromophenol Blue is a pH indicator (pH 3.4 yellow - 4.6 purple) and a tracking dye for nucleic acid or protein electrophoresis in agarose or polyacrylamide gels. Due to the slightly negative charge, the dye will migrate to the anode during electrophoresis, which allows monitoring of the movement of the molecules through the gel.