Bromophenol blue

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Bromophenol blue
Skeletal formula of bromophenol blue in cyclic form
Ball-and-stick model of the bromophenol blue molecule in cyclic form
Preferred IUPAC name
3D model (JSmol)
ECHA InfoCard 100.003.715 Edit this at Wikidata
  • InChI=1S/C19H10Br4O5S/c20-12-5-9(6-13(21)17(12)24)19(10-7-14(22)18(25)15(23)8-10)11-3-1-2-4-16(11)29(26,27)28-19/h1-8,24-25H checkY
  • InChI=1/C19H10Br4O5S/c20-12-5-9(6-13(21)17(12)24)19(10-7-14(22)18(25)15(23)8-10)11-3-1-2-4-16(11)29(26,27)28-19/h1-8,24-25H
  • Brc1cc(cc(Br)c1O)C3(OS(=O)(=O)c2ccccc23)c4cc(Br)c(O)c(Br)c4
Molar mass 669.96 g·mol−1
Odor odorless
Density 2.2 g/mL[1]
Melting point 273 °C (523 °F; 546 K)
Boiling point 279 °C (534 °F; 552 K)
Acidity (pKa) 4.0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Bromophenol blue (3′,3″,5′,5″-tetrabromophenolsulfonphthalein, BPB),[2] albutest[3] is used as a pH indicator, an electrophoretic color marker, and a dye. It can be prepared by slowly adding excess bromine to a hot solution of phenolsulfonphthalein in glacial acetic acid.[4]

Acid–base indicator[edit]

Bromophenol blue (pH indicator)
below pH 3.5 above pH 4.6
3.5 4.6

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.[5] Bromophenol blue is structurally related to phenolphthalein (a popular indicator).

Color marker[edit]

Bromophenol is also used as a colour 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. Xylene cyanol and orange G may also be used for this purpose.[6]


Bromophenol blue is also used as a dye. At neutral pH, the dye absorbs red light most strongly and transmits blue light. (Its peak absorbance is 600 nm at a basic pH of 12.) Solutions of the dye, therefore, are blue. At low pH, the dye absorbs ultraviolet and blue light most strongly and appears yellow in solution. In solution at pH 3.6 (in the middle of the transition range of this pH indicator) obtained by dissolution in water without any pH adjustment, bromophenol blue has a characteristic green red colour, where the apparent colour shifts depending on the concentration and/or path length through which the solution is observed. This phenomenon is called dichromatic color.[7] Bromophenol blue is the substance with the highest known value of Kreft's dichromaticity index.[8] This means it has the largest change in colour hue, when the thickness or concentration of observed sample increases or decreases.

See also[edit]


  1. ^ "Bromophenol Blue (CAS 115-39-9) Properties". Santa Cruz Biotechnology, Inc. Retrieved 2022-03-17.
  2. ^ Reaxys. Bromophenol blue (115-39-9) Chemical Names and Synonyms.
  3. ^ "Bromphenol Blue - Compound Summary". PubChem Compound. Retrieved 2022-03-17.
  4. ^ "Bromphenol Blue - Use and Manufacturing". PubChem Compound. Retrieved 2022-03-17.
  5. ^ "Product Specification : Bromophenol Blue" (PDF). Retrieved 2022-03-17.
  6. ^ "Agarose gel electrophoresis (basic method)". Retrieved 2008-04-07.
  7. ^ Kreft S, Kreft M (2007). "Physicochemical and physiological basis of dichromatic colour". Naturwissenschaften. 94 (11): 935–9. Bibcode:2007NW.....94..935K. doi:10.1007/s00114-007-0272-9. PMID 17534588.
  8. ^ Kreft S, Kreft M. (2009). "Quantification of dichromatism: a characteristic of color in transparent materials". Journal of the Optical Society of America A. 26 (7): 1576–1581. Bibcode:2009JOSAA..26.1576K. doi:10.1364/JOSAA.26.001576. PMID 19568292.

External links[edit]