What is "murexide test"

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 detecting tests such as Dragendorff's reagent. In this test the alkaloids 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 vapor. Purine alkaloids produce a pink color in this test. Murexide (ammonium purpurate) with a purple color is also produced in this test.