Murexide test

Murexide test. Place about o-i g. of uric acid in a small evaporating-basin and moisten with 2 3 drops of cone. HNO3. Heat very gently to dryness, and then add i drop of aqueous NHj from a glass rod a purple coloration is produced due to the formation of ammonium purpurate or murexide. Now add a drop of NaOH solution the coloration changes to blue. 

Caffeine and other purine derivatives can be detected by the Murexide test. In this test the alkaloids are mixed with a tiny amount of potassium chlorate and a drop of hydrochloric acid and evaporated to dryness, and the resulting residue is exposed to ammonia vapour. Purine alkaloids produce pink colour in this test. 

The Murexide Test.—Evaporate a little uric acid and dilute HN03 to dryness. Add few drops of ammonia to the red residue when cold purple coloration. Uric acid reduces Fehling s solution on prolonged boiling. 

Murexide test—Treat with a crystal KC103 and a few drops of HC1, evaporate to dryness the red residue turns purple with ammonia. 

With hydrazine hydrochloride, thioindoxyl-1,1-dioxide has been reported to afford the azine (110) by prior formation of a bishydrazone.132 Murexide (111), a purple indicator used in compleximetric titrations, is formed from ammonium acetate, glacial acetic acid, and alloxantin (152 R = H). The murexide test is well known for detecting uric acid and other purines.133... 

Oxidation of xanthine or uric acid derivatives with chromic acid gives the appropriate alloxane and urea as primary products which undergo further oxidation to corresponding parabanic acids (imidazolidine-2,4,5-triones) and purpuric acids which, on addition of ammonia, constitute the murexide test. This is positive for all purines capable of oxidation to an alloxane derivative, For a review see ref 48. 

Analytical Chakactebs.—Uric arid may be recognized by its ciystalline form and by tbe murexid test. To apply this test the substance is moistened with HNO, which is evaporated nemly to dryness at a low temperature the cooled residue is then moistened with ammonium hydrate. If uric acid be present, a yellow residue— sometimes pink or red wCen the uric acid was abundant—remains after the evaporation of the HNO, and this, on the addition of tbe alkali, assumes a rich purplish-red color. 

Double refraction of the various crystal forms was unaltered after staining X-ray-diffraction (X.R.D ) analysis revealed that the single sword-shaped crystal was tri—oxy-purine di-hydrate with and without methylene blue. The murexide test could be carried out even with stained crystals. 

Uric acid can be detected in renal stones by the murexide test. 

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