Solubility of uric acid in salt solutions and artificial urine

The solubility of anhydrous ur ic acid was measured at 37.0 degrees C in different salt solutions (ionic strength: 0.300 mol . dm(-3)) occasionally containing organic compounds and in standard reference artificial urine. The results did not significantly differ from the solubilities obtained previously in 0.150 mol . dm(-3) NaCl. All data measured in our laboratory can therefore be represented by a single set of two equilibrium constants, i.e. a solubility and a deprotonation constant. It is noteworthy that in these experiments the uric acid solutions were supersaturated with respect to most of the corresponding hydrogenurate salts. If combination glass electrodes calibrated in standard buffer solutions are used for the pH measurement, uric acid solubilities can be calculated by the relation [U](tot) = K-s(1 + K-1'/10(-pH)) where pK(1)' = 5.33 and pK(s) = 3.50 or 3.21 for anhydrous uric acid or uric acid dihydrate, respectively.