The stability of uric acid in ammonium hydroxide

We examined the stability of uric acid in dilute aqueous ammonium hydroxide solution by mass spectrometry. Uric acid decomposes in ammonium hydroxide even as dilute as 15 mmol/L when the mole ratio of ammonium hydroxide to uric acid is 50:1. There are at least four products of the decomposition, two of which have been identified as allantoin and urea. The slope of the decomposition curve indicates that uric acid is destroyed at an initial rate of 2-3% per hour. In ammonium hydroxide at a concentration of 1 mmol/L and a mole ratio of ammonium hydroxide to uric acid of less than or equal to 3.4, uric acid is not detectably decomposed. Evidently, any method for determination of uric acid that involves treating the analyte with ammonium hydroxide before analysis may destroy it. Therefore, a published method described as being "definitive" for uric acid (J Clin Chem Clin Biochem 1985; 23:129-35) could produce incorrect results because it involves storing the uric acid in 15 mmol/L ammonium hydroxide at a mole ratio of ammonium hydroxide to uric acid of greater than 120:1.