Phenol Red

Phenol Red is a phenolsulfonphthalein compound. It is present as a sulfonated hydroxyquinone in weakly acidic aqueous solutions. In alkaline solutions, the dye forms a hydrophilic dianion (a small, red anion and has a larger conjugated system than the yellow hydroxyquinone).

Suitable for use as a pH indicator.

Phenol red is commonly used as a pH indicator in biology and medicine. It is incorporated into microbiological culture media for the identification of Escherichia coli strains. Its clinical diagnostic applications include investigation of gastric and duodenal ulcers and in the assessment of tear function in ophthalmology. Phenol red is also used as a tracer to assess the permeability of the ileal mucosal membrane and to assess bacterial leakage through root-filling materials in dentistry.