Metacresol purple or ''m''-cresol purple, also called ''m''-cresolsulfonphthalein, is a

triarylmethane dye Triarylmethane dyes are synthetic organic compounds containing triphenylmethane backbones. As dyes, these compounds are intensely colored. They are produced industrially as dyes. Families Triarylmethane dyes can be grouped into families accordin ...

and a

pH indicator A pH indicator is a halochromism, halochromic chemical compound added in small amounts to a Solution (chemistry), solution so the pH (acidity or Base (chemistry), basicity) of the solution can be determined visually or spectroscopically by chang ...

. It is used as a capnographic indicator for detecting detect end-tidal

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

to ensure successful

tracheal intubation Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic catheter, tube into the vertebrate trachea, trachea (windpipe) to maintain an open airway or to serve as a conduit through which to administer c ...

in an emergency. It can be used to measure the pH in subzero temperatures of saline or hypersaline media. In

colorimetric capnography Colorimetric capnography is a qualitative measurement method that detects the presence of carbon dioxide (CO2, a relatively acidic gas) in a given gaseous environment. From a medical perspective, the method is usually applied by exposing litmus ...

, the indicator is incorporated in an

aqueous An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, also known as sodium chloride (NaCl), in wat ...

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 Carbonic acid is a chemical compound with the chemical formula . The molecule rapidly converts to water and carbon dioxide in the presence of water. However, in the absence of water, it is quite stable at room temperature. The interconversion ...

. In chemistry, it has two useful indicator ranges: * pH 1.2–2.8: red to yellow * pH 7.4–9.0: yellow to purple

References

PH indicators Chemicals in medicine Triarylmethane dyes Phenol dyes Purple {{organic-compound-stub

See also

References