Products / pH Indicators

m-CRESOL PURPLE Print Download

C.A.S. No. 2303-01-7
M.F. C21H18O5S
M.W. 382.43gm/mole


Appearance Green to Brown Powder
Transition Range pH 7.4-9.0
Brownish Yellow-Violet
Solubility 0.1%(50% EtOH) Clear solution
Absorption maximum (0.1N NaOH) ?max 578-584nm
Absorptivity 1%,1cm,(0.1 N NaOH, at ?max) 800-900
Loss On Drying (110°C) <3%

Chemical Name

Phenol, 4,4'-(3H-2,1-benzoxathiol-3-ylidene)bis[3-methyl-, S,S-dioxide

InChI Key



Very slightly soluble in water, ethanol; soluble in methanol

Product Description:

m-Cresol Purple is a pH indicator dye used primarily in spectrophotometric pH measurement. It operates in the pH ranges 1.2 - 2.8 (red to yellow) and 7.4 - 9.0 (yellow to violet). Further, it is employed to stain epithelial cells and proteins.A chemical structure of a molecule includes the arrangement of atoms and the chemical bonds that hold the atoms together. The m-Cresol purple molecule contains a total of 48 bond(s). There are 30 non-H bond(s), 20 multiple bond(s), 2 rotatable bond(s), 2 double bond(s), 18 aromatic bond(s), 1 five-membered ring(s), 3 six-membered ring(s), 1 nine-membered ring(s), 2 aromatic hydroxyl(s) and 1 sulfonate(s) (thio-/dithio-).


Accurate pH measurements in polar waters and sea ice brines require pH indicator dyes characterized at near-zero and below-zero temperatures and high salinities. We present experimentally determined physical and chemical characteristics of purified meta-Cresol Purple (mCP) pH indicator dye suitable for pH measurements in seawater and conservative seawater-derived brines at salinities (S) between 35 and 100 and temperatures (T) between their freezing point and 298.15 K (25 °C). Within this temperature and salinity range, using purified mCP and a novel thermostated spectrophotometric device, the pH on the total scale (pHT) can be calculated.m-Cresol Purple is a recommended indicator for open-ocean pH measurements. The compound is used in many colorimetric sensor studies.

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