o-Cresolphthalein

white to pink or beige to tan powder. soluble in ethanol, ether, glacial acetic acid, soluble in dilute alkali and turns purple, slightly soluble in water, hardly soluble in benzene.

O-Cresolphthalein has been used as a component in calcifying media for calcification assay. It is also used as an indicator (pH range, 8.2 colorless, 9.8 red) and analytical reagent.

O-Cresolphthalein is a gadolinium chelate that is used as a contrast agent for magnetic resonance imaging (MRI) of the brain, spine, and joints. The gadolinium ion is bound to the cresol molecule, which has an attached hydroxyl group. This complex attaches to the phosphorous pentoxide and creates a precipitate of metal hydroxides in the presence of water and sodium carbonate. O-Cresolphthalein is also used in clinical pathology to measure glomerular filtration rate (GFR), which is important for diagnosing renal disease. MRI scans are used to diagnose osteogenic genes that are associated with bone diseases such as osteoporosis.

o-Cresolphthalein is a reversible pH indicator. The kinetics of the reverse pathway (red-purple to colorless) is slow, thereby making it an appropriate molecule to check flow patterns in ducts with corrugated walls. It is also used for the colorimetric determination of calcium content via the o-cresolphthalein complexone method. Binding of calcium to o-cresolphthalein, in the presence of alkaline conditions (pH 10-12), results in the formation of a red complex with an absorbance at 570-575nm.