title: Simultaneous quantitation of homocysteine, cysteine and methionine in plasma and urine by liquid chromatography-tandem mass spectrometry.
abstract: BACKGROUND
  A method utilizing liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS) has been developed and evaluated for the determination of total homocysteine, cysteine and methionine in plasma and urine. The simultaneous measurement of homocysteine and methionine concentrations may help explain the underlying mechanism responsible for hyperhomo-cysteinaemia.
  
  
  METHODS
  Samples were prepared by simple protein precipitation after reduction of disulphides by dithiothreitol. Reduced analyte signal caused by ionization suppression effects, seen with plasma samples, was compensated for with matrix-matched standards, and the use of isotopically labelled internal standards. Recovery for each analyte was better than 94%.
  
  
  RESULTS
  Concentrations of plasma homocysteine determined by LC-MS/MS were compared with those obtained by two automated commercially available FDA-approved procedures: (i) high-performance liquid chromatography (HPLC) with pre-column derivatization and fluorescence detection and (ii) by fluorescence polarization immunoassay (FPIA). Agreement with the LC-MS/MS method is given by the Deming regression equations LC-MS/MS = 1.062 HPLC-0.01 and LC-MS/MS = 1.104 FPIA-0.43.
  
  
  CONCLUSIONS
  Low reagent costs together with the relative simplicity of sample preparation make the LC-MS/MS method well suited, not only for research work but also in those laboratories with a tandem mass spectrometer, for the measurement of routine clinical samples.
authors.affiliation: Clinical Chemistry and Immunology Department, Royal Sussex County Hospital, Brighton and Sussex University Hospitals NHS Trust, Brighton BN2 5BE, UK. gary.weaving@bsuh.nhs.uk
authors.forename: G
authors.initials: G
authors.lastname: Weaving
authors.forename: B F
authors.initials: BF
authors.lastname: Rocks
authors.forename: S A
authors.initials: SA
authors.lastname: Iversen
authors.forename: M A
authors.initials: MA
authors.lastname: Titheradge
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003545:Cysteine / Q000097:blood* / Q000652:urine*; D003553:Cystine / Q000097:blood; D006710:Homocysteine / Q000097:blood* / Q000652:urine*; D006801:Humans; D008715:Methionine / Q000097:blood* / Q000652:urine*; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D006710:Homocysteine; D003553:Cystine; D008715:Methionine; D003545:Cysteine