Bromophenol blue (3′,3″,5′,5″-tetrabromophenolsulfonphthalein, BPB), albutest is used as a
pH indicator
A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. Hen ...
, 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.
Acid–base indicator
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 structurally related to
phenolphthalein (a popular indicator).
Color marker
Bromophenol is also used as a colour marker to monitor the process of
agarose gel electrophoresis
Agarose gel electrophoresis is a method of gel electrophoresis used in biochemistry, molecular biology, genetics, and clinical chemistry to separate a mixed population of macromolecules such as DNA or proteins in a matrix of agarose, one of ...
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
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...
in a gel; the rate at which it migrates varies according to gel density and
buffer composition, but in a typical 1%
agarose
Agarose is a heteropolysaccharide, generally extracted from certain red seaweed. It is a linear polymer made up of the repeating unit of agarobiose, which is a disaccharide made up of D-galactose and 3,6-anhydro-L-galactopyranose. Agarose is ...
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.
Dye
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.
Bromophenol blue is the substance with the highest known value of
Kreft's dichromaticity index.
This means it has the largest change in colour
hue, when the thickness or concentration of observed sample increases or decreases.
See also
*
Bromophenol
References
External links
Bromophenol blueat OpenWetWare
{{DEFAULTSORT:Bromophenol Blue
PH indicators
Triarylmethane dyes
Phenol dyes
Bromoarenes
Benzoxathioles