Cresol purple

Metacresol purple
Identifiers

CAS Number	2303-01-7
3D model (JSmol)	Interactive image
ChemSpider	2006272
ECHA InfoCard	100.017.237
PubChem CID	73030
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⁻¹
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Metacresol purple or m-cresol purple, also called m-cresolsulfonphthalein is a triarylmethane dye and a pH indicator that is used in medicine to detect end-tidal carbon dioxide to ensure successful tracheal intubation in an emergency as the indicator inside a colorimetric carbon dioxide detector.

In colometric capnography the indicator is incorporated in a matrix that provides a pH just above the indicator's colour change, it undergoes the colour change from purple to yellow with CO₂; (a yellow colour often described as gold) when CO₂ dissolves as CO₂ is acidic.

In chemistry, it has two useful indicator ranges:

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