title: An on-line solid phase extraction procedure for the routine quantification of urinary methylmalonic acid by liquid chromatography-tandem mass spectrometry.
abstract: BACKGROUND
  The goal of this study was to develop and to validate an improved isotope-dilution-liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of methylmalonic acid (MMA) in urine.
  
  
  METHODS
  A previously described sample preparation protocol requires two solvent extraction steps, including evaporation. The first extraction is to extract the analyte from the sample, and second occurs following derivatization of the extract. In the method described here, the second evaporation step was substituted by on-line solid phase extraction employing column-switching and a permanent co-polymer based extraction cartridge. A standard validation protocol was applied to investigate the performance of the method.
  
  
  RESULTS
  The method was found to be linear in the clinically relevant range of concentrations (6-100 μmol/L). Total coefficients of variation were below 10% and inaccuracy was <10% for quality control samples at three concentrations.
  
  
  CONCLUSIONS
  By omitting one evaporation step, the semi-automated method described in this article enables for more convenient work-flow in the quantification of urinary MMA compared to the previous protocol. This is of relevance for MMA measurement in the routine clinical laboratory setting. Validation demonstrated acceptable analytical performance.
authors: Institute of Clinical Chemistry, Hospital of the University of Munich, Munich, Germany. Fabian.Kirchhoff@med.uni-muenchen.de
authors: Fabian
authors: F
authors: Kirchhoff
authors: Stephan
authors: S
authors: Lorenzl
authors: Michael
authors: M
authors: Vogeser
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D008764:Methylmalonic Acid / Q000302:isolation & purification* / Q000652:urine*; D015203:Reproducibility of Results; D052616:Solid Phase Extraction / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*; D016482:Urinalysis / Q000379:methods*
chemical_list: D008764:Methylmalonic Acid