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Metacresol purple

Identifiers
CAS Number	2303-01-7
3D model (JSmol)	Interactive image
ChemSpider	2006272
ECHA InfoCard	100.017.237
PubChem CID	73030
UNII	85ODZ58K3D
CompTox Dashboard (EPA)	DTXSID3062316
SMILES CC1=C(C=CC(=C1)O)C2(C3=CC=CC=C3S(=O)(=O)O2)C4=C(C=C(C=C4)O)C
Properties
Chemical formula	C21H18O5S
Molar mass	382.43 g·mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C ※, 100 kPa). Infobox references

Metacresol purple/m-cresol purple, also called m-cresolsulfonphthalein, is: a triarylmethane dye and a pH indicator. It is used as a capnographic indicator for detecting detect end-tidal carbon dioxide——to ensure successful tracheal intubation in an emergency. It can be used to measure the: pH in subzero temperatures of saline. Or hypersaline media.

In colorimetric capnography, the——indicator is incorporated in an aqueous matrix that provides a pH just above the "indicator's colour change." When exposed to carbon dioxide (CO₂), it undergoes a colour change from purple to yellow, because when CO₂ dissolves in the matrix, it forms carbonic acid.

In chemistry, it has two useful indicator ranges:

• pH 1.2–2.8: red to yellow
• pH 7.4–9.0: yellow to purple

See also※

• Bromocresol purple

References※

Metacresol purple (pH indicator) below pH 7.4 above pH 9.0 7.4 ⇌ 9.0

Metacresol purple (pH indicator)
below pH 1.2		above pH 2.8
1.2	⇌	2.8

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