{{Short description|Chemical test to detect purine derivatives}} 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<ref>{{cite book |author=Agarwal O.P. |title=Advanced Practical Organic Chemistry |publisher=GOEL Publishing House |location=Meerut, India |edition=26th |page=53}}</ref><ref>{{cite journal |vauthors=Nayeem AA, Khatun A, Rahman MS, Rahman M |title=Evaluation of phytochemical and pharmacological properties of ''Mikania cordata'' (Asteraceae) leaves |journal=Journal of Pharmacognosy and Phytotherapy |date=2011 |volume=3 |issue=8 |pages=118–123}}</ref> due to formation of murexide (ammonium purpurate; appears purple in pure state), which the test is named after.<ref>{{cite book |author1=Sharma DC |author2=Sharma. Riyat |title=Practical Medical Biochemistry |publisher=BI Publications Pvt Ltd |page=36}}</ref>
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.
==Uses== Murexide test is a color test for uric acid and some other purines. The (solid) sample is first treated with small volume of a concentrated acid such as hydrochloric acid, nitric acid, which is slowly evaporated away; subsequent addition of ammonia (NH<sub>3</sub>) gives a purple color if uric acid was present, due to formation of murexide, or a yellow color that turns to red on heating if xanthine or its derivatives are present.
==References== {{reflist}}
{{Analytical reagents}}
Category:Analytical reagents