Murexide test
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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 test. 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.[3]
In pure form, murexide appears purple, but when it is produced by reaction of acidified solutions of purines and ammonia, various shades of purple and pink are produced.
