Metacresol purple

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]

Metacresol purple
Identifiers
CAS Number
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.017.237
PubChem CID
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

In colometric 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 the colour change from purple to yellow with—a colour often described as gold—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
  1. "Capnography". LITFL • Life in the Fast Lane Medical Blog. Retrieved 2017-07-30.
  2. "m-Cresol Purple 857890". Sigma-Aldrich. Retrieved 2017-07-30.
  3. Loucaides, Socratis; Rèrolle, Victoire M. C; Papadimitriou, Stathys; Kennedy, Hilary; Mowlem, Matthew C; Dickson, Andrew G; Gledhill, Martha; Achterberg, Eric P (2017). "Characterization of meta-Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures". Scientific Reports. 7 (1): 2481. doi:10.1038/s41598-017-02624-0. PMC 5449408. PMID 28559544.
  4. Gedeon, A.; Krill, P.; Mebius, C. (1994-09-01). "A new colorimetric breath indicator (Colibri)". Anaesthesia. 49 (9): 798–803. doi:10.1111/j.1365-2044.1994.tb04457.x. ISSN 1365-2044. PMID 7978140.
  5. Hagberg, Carin A. (2007-02-23). Benumof's Airway Management. Elsevier Health Sciences. ISBN 978-0323070171.
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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