Product Short Description: M CRESOL PURPLE INDICATOR Product Description: 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. Metacresol purple or m-cresol purple, also called m-cresolsulfonphthalein is a triarylmethane dye and a pH indicator.