Bromophenol Blue (chemical name: 3′,3″,5′,5″-tetrabromophenolsulfonphthalein) is a multifunctional compound used as a pH indicator, electrophoresis tracking dye, and general-purpose stain. It is synthesized by slowly adding excess bromine to a hot solution of phenolsulfonphthalein in glacial acetic acid.
🏭⚗️ Production
Bromophenol Blue is produced by gradually introducing excess bromine into a hot solution of phenolsulfonphthalein dissolved in glacial acetic acid.
🧪 Applications
1. pH Indicator
The dye changes color depending on the pH level: it appears blue in basic environments and yellow in acidic conditions. Around pH 3.6 (its transition point), the color can shift between green and red depending on the concentration and thickness of the solution—a phenomenon known as dichromaticity. Bromophenol Blue has the highest known Kreft’s dichromaticity index, indicating a strong color hue change with varying sample thickness or concentration.
2. Electrophoresis Tracking Dye
In agarose or polyacrylamide gel electrophoresis, Bromophenol Blue acts as a color marker. Due to its slight negative charge at moderate pH, it migrates in the same direction as DNA or protein. In a 1% agarose gel, it moves at a rate similar to a 300 base pair DNA fragment, and in 2% agarose, similar to a 150 bp fragment.
3. Dye/Colorant
At neutral pH, the dye strongly absorbs red light (peak absorbance ~590 nm at pH 12) and appears blue. At lower pH, it absorbs ultraviolet and blue light, resulting in a yellow appearance.
