Metacresol purple explained

Metacresol purple or 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.^{[1] [2]} It can be used to measure the pH in subzero temperatures of saline or hypersaline media.^[3]

In colorimetric capnography, the indicator is incorporated in an aqueous matrix that provides a pH just above the indicator's colour change.^[4] 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.^[5]

In chemistry, it has two useful indicator ranges:^[2]

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

See also

• Bromocresol purple

References

Notes and References

1. News: Capnography. LITFL • Life in the Fast Lane Medical Blog. 2017-07-30. en-US.
2. Web site: m-Cresol Purple 857890. Sigma-Aldrich. 2017-07-30.
3. Characterization of meta-Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures. Scientific Reports. 7. 1. 2481. 10.1038/s41598-017-02624-0. 28559544. 5449408. 2017. Loucaides. Socratis. Rèrolle. Victoire M. C. Papadimitriou. Stathys. Kennedy. Hilary. Mowlem. Matthew C. Dickson. Andrew G. Gledhill. Martha. Achterberg. Eric P. 2017NatSR...7.2481L.
4. Gedeon. A.. Krill. P.. Mebius. C.. 1994-09-01. A new colorimetric breath indicator (Colibri). Anaesthesia. en. 49. 9. 798–803. 10.1111/j.1365-2044.1994.tb04457.x. 7978140. 44501202. 1365-2044. free.
5. Book: Hagberg, Carin A.. Benumof's Airway Management. 2007-02-23. Elsevier Health Sciences. 978-0323070171. en.