4.10. Uric Acid
The uric acid content in the plasma samples was measured using HPLC-ESI-MS/MS with isotope labelled 1,3-Analysis of the samples was performed with an HPLC Agilent 1100 Series equipped with a degasser (G1322A), quaternary pump (G1311A), autosampler (G1313A), column oven (G1316A) (Agilent Technologies, Santa Clara, CA, USA) and coupled an API 2000 triple-quadrupole mass spectrometer (Applied Biosystems, Framingham, MA, USA) with ESI source. Liquid chromatography analyses were performed in a gradient elution mode using Phenomenex Luna 5 μm C18(2) 100Å (250 mm × 4.6 mm) column (Phenomenex, Aschaffenburg, Germany) coupled with a Phenomenex Luna C8(2), 5 μm particle size guard column. The mobile phase used included 5 mM ammonium acetate/0.1% acetic acid (A) and acetonitrile/0.1% formic acid (B). The mobile phase flow was 0.9 mL min