Products / pH Indicators


C.A.S. No. 2411-89-4
M.F. C32H32N2 O12
M.W. 636.62gm/mole


Solubility 0.1% (0.1N NaOH) Clear solution
Absorption maximum (0.1N NaOH) at ?max 572-578nm
Absorptivity (A1%1cm in 0.1N NaOH, at ?max on dried substance) >790
Loss On Drying (110°C) <6%

Chemical Name

2-[[5-[1-[3-[[bis(carboxymethyl)amino]methyl]-4-hydroxy-5-methylphenyl]-3-oxo-2-benzofuran-1-yl]-2-hydroxy-3-methylphenyl]methyl-(carboxymethyl)amino]acetic acid

InChI Key



Water Solubility: Slightly soluble. Soluble in NaOH (50 mg/ml), aqueous ammonia, and organic solvents.

Product Description:

o-Cresolphthalein Complexone is complexometric reagent derived from o-Cresolphthalein. It shows violet-red color in alkaline media and is a principle compound for the determination of hardness of water.Also used as Calcium Assay Kit as direct colorimetric assay based on the O-Cresolphtalein (OCPC) method without deproteinization of the sample. The calcium determination is based on the reaction of calcium with O-Cresolphthalein complexone in alkaline solution, which yields a violet colored complex. The intensity of the color formed is proportional to the calcium concentration in the sample. Absorbance of the Ca2+-O-Cresolphtalein complex is measured at 570nm. Wavelength range of sensitivity: 560 ~ 590nm.


o-Cresolphthalein Complexone (OCPC) method is used for colorimetric estimation of calcium in serum and determination of Magnesium, Strotium and Barium. This method is rapid, simple and ideal for routine use in clinical laboratory. Calcium in alkaline medium reacts with o-Cresolphthalein Complexone to form a purple colored complex whose absorbance is proportional to the calcium concentration. o-Cresolphthalein complexone reagent system is used for the determination of calcium in plasma or serum having increased stabillity through the use of a carbonate or bicarbonate buffer system.

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