Bromocresol green (BCG) is a dye of the

triphenylmethane Triphenylmethane, or triphenyl methane, is the hydrocarbon with the formula (C6H5)3CH. This colorless solid is soluble in nonpolar organic solvents and not in water. Triphenylmethane is the basic skeleton of many synthetic dyes called triarylmetha ...

family (

triarylmethane dye Triarylmethane dyes are synthetic organic compounds containing triphenylmethane backbones. As dyes, these compounds are intensely colored. They are produced industrially as dyes. Families Triarylmethane dyes can be grouped into families accordin ...

s). It belongs to a class of dyes called sulfonephthaleins. It is used as a pH indicator in applications such as growth mediums for microorganisms and titrations. In clinical practise, it is commonly used as a diagnostic technique. The most common use of bromocresol green is to measure serum albumin concentration within mammalian blood samples in possible cases of

kidney failure Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...

and liver disease.

Properties

aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...

, bromocresol green will

ionize Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...

to give the monoanionic form (yellow), that further deprotonates at higher pH to give the dianionic form (blue), which is stabilized by

resonance Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...

: :

The

acid dissociation constant In chemistry, an acid dissociation constant (also known as acidity constant, or acid-ionization constant; denoted ) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction :HA ...

(p''K''_a) of this reaction is 4.8. Tap water is sufficiently basic to give a solution of bromocresol green its characteristic blue-green color. Bromocresol green spectrum

The acid and basic forms of this dye have an

isosbestic point In spectroscopy, an isosbestic point is a specific wavelength, wavenumber or frequency at which the total absorbance of a sample does not change during a chemical reaction or a physical change of the sample. The word derives from two Greek words ...

in their UV-Visible spectrum, around 515 nm, indicate that the two forms interconvert directly without forming any other substance. An

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...

solution (0.04 wt%) of bromocresol green has been proposed for TLC staining and is suitable for visualisation of the compounds with functional groups whose p''K''_a is below 5.0 (carboxylic acids, sulfonic acids, etc.). These appear as yellow spots on a light or dark blue background; no heating is necessary.

Bromophenol blue Bromophenol blue (3′,3″,5′,5″-tetrabromophenolsulfonphthalein, BPB), albutest 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 phenolsulfonpht ...

solution can be used for the same purpose. The compound is synthesized by bromination of

cresol purple Metacresol purple or ''m''-cresol purple, also called ''m''-cresolsulfonphthalein, is a triarylmethane dye and a pH indicator. It is used as a capnographic indicator for detecting detect end-tidal carbon dioxide to ensure successful tracheal intu ...

(''m''-cresolsulfonphthalein).

Uses

It 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. Hence, ...

and as a tracking dye for DNA

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 the ...

. It can be used in its free acid form (light brown solid), or as a

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

(dark green solid). It is also an inhibitor of the prostaglandin E₂ transport protein. Additional applications include use in sol-gel matrices, the detection of ammonia, and the measurement of albumin in human plasma and serum.

Safety

Bromocresol green may cause irritation. Skin and eye contact should be avoided.

References

{{reflist PH indicators Triarylmethane dyes Phenol dyes Bromoarenes Benzoxathioles