Products / pH Indicators


C.A.S. No. 1733-12-6
M.F. C21H18O5S
M.W. 382.43gm/mole


Dye Content (by Spectrophotometry) >95%
Transition Range pH 6.5-8.8
Solubility 0.1% (95% EtOH) Clear solution
Absorption maximum (pH 6.5) ?1max 432-436nm
Absorption maximum (pH 8.8) ?2max 571-574nm
Absorptivity (A1%/1cm at pH 6.5 at ?1max) 490-540
Absorptivity (A1%/1cm at pH 8.8 at ?2max) 1000-1100
Loss On Drying (110°C) <3%

Chemical Name


InChI Key



Insoluble in water; soluble in alcohol and in solutions of alkali hydroxides. Solubility in other solvents: soluble in dil. alkalies and ethanol, insoluble in diethyl ether, benzene.

Product Description:

Cresol red (full name: o-cresolsulfonephthalein) is a dye C21H18O5S of the sulfonephthalein series derived from ortho-cresol that is obtained as a reddish brown crystalline powder and is used as an acid-base indicator. It is a triarylmethane dye frequently used for monitoring the pH in aquaria.


Cresol Red can be used in many common molecular biology reactions in place of other loading dyes. Cresol Red does not inhibit Taq polymerase to the same degree as other common loading dyes. Cresol Red can also be used as a color marker to monitor the process of agarose gel electrophoresis and polyacrylamide gel electrophoresis. Triarylmethane dye commonly used with lead acetate for the detection of urease after polyacrylamide gel electrophoresis (PAGE). Also used as a pH indicator and as a tracking dye in DNA, RNA (agarose) and protein (polyacrylamide) electrophoresis. In agarose, Cresol Red runs with an apparent molecular size of approximately 125 bp DNA. Cresol Red does not inhibit Taq polymerase

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