Bromocresol green


Bromocresol green is a dye of the triphenylmethane family. 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 and liver disease.

Properties

In aqueous solution, bromocresol green will ionize to give the monoanionic form, that further deprotonates at higher pH to give the dianionic form, which is stabilized by resonance:
The acid dissociation constant of this reaction is 4.8. Tap water is sufficiently basic to give a solution of bromocresol green its characteristic blue-green color.
occurs where the acid and basic forms and mixtures thereof have the same absorbance
The acid and basic forms of this dye have an isosbestic point in their UV-Visible spectrum, around 515 nm, indicate that the two forms interconvert directly without forming any other substance.
An ethanol solution of bromocresol green has been proposed for TLC staining and is suitable for visualisation of the compounds with functional groups whose pKa is below 5.0. These appear as yellow spots on a light or dark blue background; no heating is necessary. Bromophenol blue solution can be used for the same purpose.
The compound is synthesized by bromination of cresol purple.

Uses

It is used as a pH indicator and as a tracking dye for DNA agarose gel electrophoresis. It can be used in its free acid form, or as a sodium salt. 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.