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Clinical Chemistry 52: 2117-2118, 2006; 10.1373/clinchem.2006.077669
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(Clinical Chemistry. 2006;52:2117-2118.)
© 2006 American Association for Clinical Chemistry, Inc.

Letters to the Editor

Preparation of Uric Acid Standard Stock Solution

Dai Xinhua

National Institute of Metrology, National Research Center, for Certified Reference Materials, Beijing, 100013 China, Fax 86-10-64279562, E-mail xhdai_75{at}iccas.ac.cn


To the Editor:

For measurement of uric acid in serum, calibrators of known concentration must be prepared in a suitable solvent. Uric acid is virtually insoluble in water or common organic solvents, but it can be dissolved in basic solution such as aqueous solutions of Li2CO3 (1), KOH (2), NaOH(3), and ammonium hydroxide (4)(5). Siekmann(4) used ammonium hydroxide as the solvent for dissolving uric acid at a molar ratio of ammonium hydroxide to uric acid of ~120:1. Ellerbe et al. (5) used ammonium hydroxide as the solvent for dissolving uric acid at a ratio of ammonium hydroxide to uric acid of 1.7:1. In addition, Ellerbe et al. (5) showed that uric acid is stable in ammonium hydroxide at a molar ratio of 1.7:1.

We are working to develop a new definitive method for serum uric acid by use of HPLC-isotope dilution mass spectrometry (HPLC-ID/MS). We prepared a stock standard solution of uric acid in 1 mmol/L ammonium hydroxide at a molar ratio of 1.7:1, according to Ellerbe’s method. But uric acid was not dissolved completely after several hours to several days. We changed the concentration of ammonium hydroxide from 1 mmol/L to 2 mmol/L. We again prepared a standard solution of uric acid at the same molar ratio of 1.7:1 with this concentration of 2-mmol/L ammonium hydroxide. With this ammonium hydroxide concentration, uric acid dissolved completely in a few minutes. The standard solution was stable at least 3 months stored in a well-stoppered brown, all-glass container at –20 °C. Ammonium hydroxide was selected because it was suitable for mass spectrometric analyses and also because uric acid was stable in the ammonium hydroxide solution. We therefore recommend the use of 2 mmol/L ammonium hydroxide, not 1 mmol/L ammonium hydroxide or other basic solutions, to prepare uric acid standard solutions.


References

  1. Pachla LA, Kissinger PT. Measurement of serum uric acid by liquid chromatography. Clin Chem 1979;25:1847-1852.[Free Full Text]
  2. Ismail AAA, Dakin TA. Gas chromatography and characterization of tetraethyl derivatives of uric acid. J Chromatogr 1975;110:182-186.[CrossRef][ISI][Medline] [Order article via Infotrieve]
  3. Milner JA, Perkins EG. Determination of uric acid in biological fluids by high performance liquid chromatography. Anal Biochem 1978;88:560-565.[CrossRef][ISI][Medline] [Order article via Infotrieve]
  4. Siekmann L. Determination of uric acid in human serum by isotope dilution mass spectrometry. J Clin Chem Clin Biochem 1985;23:129-135.[ISI][Medline] [Order article via Infotrieve]
  5. Ellerbe P, Cohen A, Welch MJ, White VE. The stability of uric acid in ammonium hydroxide. Clin Chem 1988;34:2280-2282.[Abstract/Free Full Text]




This Article
Right arrow Extract Freely available
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the Editor about this paper
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Right arrow Articles by Xinhua, D.
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PubMed
Right arrow PubMed Citation
Right arrow Articles by Xinhua, D.
Related Collections
Right arrow General Clinical Chemistry

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