The murexide test is an analytical technique to identify the presence of caffeine and other purine derivatives in a sample.
These compounds do not respond to the common alkaloid identification tests such as Dragendorff's reagent.
In this test, crude drugs (to be identified) are mixed with a tiny amount of potassium chlorate and a drop of hydrochloric acid.
The sample is then evaporated to dryness and the resulting residue is exposed to ammonia vapour.
Purine alkaloids produce a pinkish-purple color in this test[1][2] due to formation of murexide (ammonium purpurate; appears purple in pure state), which the test is named after.