Determination of uric acid in human serum by isotope dilution-mass spectrometry. Definitive methods in clinical chemistry, III.

A method for the measurement of uric acid in human serum by isotope dilution-mass spectrometry is described. The analytical procedure consists of the following steps: Addition of [1,3-15N2]uric acid to the serum sample; ion exchange chromatography on AG1-X2; formation of the trimethylsilyl derivative; gas liquid chromatography-mass spectrometry (GC-MS), selected ion monitoring (SIM) at m/z-values 456 and 458; calculation of the amount of uric acid in the serum sample from the isotope ratio, as measured by GC-MS. The accuracy of the method is obtained by the use of the highly specific technique of selected ion recording in combination with the exact control of recovery as performed by the isotope dilution procedure. On the basis of the high accuracy of the isotope dilution-mass spectrometry technique, the method presented here may be proposed as a definitive method in clinical chemistry. The imprecision of the method was estimated by measuring replicates in 18 lyophilised serum pools on different occasions. The coefficient of variation proved to be between 0.6 and 1.1% in the concentration range of 200 to 500 mumol/l. The lower limit of detection (ratio of signal to noise 3:1) of SIM was about 10 ng uric acid per sample.