Determination of uric acid in plasma by LC-MS/MS and its application to an efficacy evaluation of recombinant urate oxidase.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of uric acid in human plasma was developed and validated. Separation was achieved on a C18 column by the mobile phase of 30% water (containing 0.5% formic acid) and 70% methanol. Quantification was done using a multiple reaction monitoring (MRM) mode to monitor the precursor-to-product ion transitions of m/z 169.1 → m/z 141.1 for uric acid and m/z 171 → m/z 143 for 1,3-(15)N uric acid (IS) at a positive ionization mode. The calibration curve was established over the range of 0.4096 - 100 mg/L, and the correlation coefficient was better than 0.99. The intra-day and inter-day relative standard deviations were less than 5.1%. The accuracy determined at three concentrations ranged between 92.7 and 102.3%. This method was successfully applied to an efficacy study of intravenous recombinant urate oxidase produced by Escherichia coli in a clinical phase I study.