title: A novel quantitative method for recovering precipitated uric acid in urine and analysis by LC-MS/MS.
abstract: OBJECTIVE
  Precipitation of uric acid (UA) in human urine had caused poor recovery and underestimation of UA in study samples.
  
  
  RESULTS
  A UA recovery method was developed for analyzing frozen urine samples that potentially contain precipitated UA. Samples were treated with 3% v/v of a solution containing 8 M potassium hydroxide and 20% v/v of ammonium thioglycolate. The high pH enables rapid dissolution of UA crystals, while the thioglycolate protects UA from oxidation at high pH. The treated samples were diluted 20-fold with 50 mM ammonium chloride and analyzed immediately by LC-MS/MS or stored at -20°C prior to analysis.
  
  
  CONCLUSIONS
  Complete recovery of UA was achieved. Thioglycolate stabilized UA at pH 13 for at least 4.5 h at room temperature. Both accuracy and precision satisfy US FDA bioanalytical method validation (BMV) guidelines.
authors.affiliation: Ardea Biosciences, 9390 Towne Centre Drive, San Diego, CA 92121, USA.
authors.forename: Lifang
authors.initials: L
authors.lastname: Sun
authors.affiliation: Ardea Biosciences, 9390 Towne Centre Drive, San Diego, CA 92121, USA.
authors.forename: Dongmei
authors.initials: D
authors.lastname: Zhou
authors.affiliation: Ardea Biosciences, 9390 Towne Centre Drive, San Diego, CA 92121, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Wilson
mesh_terms: D002851:Chromatography, High Pressure Liquid; D005615:Freezing; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000737:chemistry; D017680:Potassium Compounds / Q000737:chemistry; D053719:Tandem Mass Spectrometry; D013696:Temperature; D013864:Thioglycolates / Q000737:chemistry; D014527:Uric Acid / Q000652:urine*
chemical_list: D006878:Hydroxides; D017680:Potassium Compounds; D013864:Thioglycolates; D014527:Uric Acid; C017487:2-mercaptoacetate; C029943:potassium hydroxide
keywords: ammonium thioglycolate; recovery; stability; supersaturation; uric acid; urine