Indicator for complexometric titration of Mg, Ca, Sr and Ba. It is used as an alkaline earth metal ion indicator. Suggested to be colorless at pH 11, but turns pink in the presence of alkaline earth metals. Also utilized in an auto analyzer to determine serum calcium.
Purification Methods
o-Cresolphthalein (a complexon precursor without the two bis-carboxymethylamino groups) is a contaminant and is one of the starting materials. It can be removed by dissolving the reagent in H2O and adding a 3-fold excess of sodium acetate and fractionally precipitating it by dropwise addition of HCl to the clear filtrate. Wash the precipitate with cold H2O and dry the monohydrate at 30o in a vacuum. The pure material gives a single spot on paper chromatography (eluting solvent EtOH/water/phenol, 6:3:1, and developing with NaOH). [Anderegg et al. Helv Chim Acta 37 113 1954.] It complexes with Ba, Ca, Cd, Mg and Sr. [Beilstein 18 III/IV 8141.]
