title: Measurement of plasma free metanephrine and normetanephrine by liquid chromatography-tandem mass spectrometry for diagnosis of pheochromocytoma.
abstract: BACKGROUND
  Quantification of plasma free metanephrines is usually accomplished by HPLC with electrochemical detection, but sample preparation is labor-intensive and time-consuming, run times are long, and interfering substances sometimes obscure the relevant peaks. The aim of this study was to develop a sensitive and specific LC-MS/MS method for plasma free metanephrines.
  
  
  METHODS
  After solid-phase extraction, chromatographic separation of normetanephrine (NMN) and metanephrine (MN) was accomplished by use of a cyano analytical column. NMN, MN, d(3)-NMN, and d(3)-MN positive ions were detected in the multiple-reaction monitoring mode using the specific transitions m/z 166-->134, 180-->148, 169-->137, and 183-->151, respectively, with an atmospheric pressure chemical ionization source.
  
  
  RESULTS
  Multiple calibration curves exhibited consistent linearity and reproducibility. Interassay imprecision values (CV; n = 20) for NMN at 0.64, 1.9, and 2.7 nmol/L were 6.6%, 7.8%, and 13%, respectively. Interassay CV for MN at 0.60, 1.2, and 2.1 nmol/L (n = 20) were 9.2%, 6.8%, and 9.8%, respectively. The mean recoveries of NMN and MN relative to the internal standard were 100% and 96%, respectively. The assays were linear between 0.20 and 10.0 nmol/L. Deming regression of HPLC and LC-MS/MS results yielded slopes of 0.93 (95% confidence interval, 0.89-0.98) and 0.89 (0.85-0.93) and y-intercepts of -0.16 and 0.03 nmol/L for NMN (n = 132) and MN (n = 92), respectively.
  
  
  CONCLUSIONS
  This novel LC-MS/MS approach provides a precise, rapid, and specific alternative method to HPLC for the quantification of the low nanomolar concentrations of free metanephrines in plasma.
authors.affiliation: Department of Laboratory Medicine & Pathology, Mayo Clinic and Foundation, 200 First Street SW, Rochester, MN 55905, USA.
authors.forename: Susan A
authors.initials: SA
authors.lastname: Lagerstedt
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: O'Kane
authors.forename: Ravinder J
authors.initials: RJ
authors.lastname: Singh
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000097:blood / Q000175:diagnosis*; D000328:Adult; D000368:Aged; D002138:Calibration; D002853:Chromatography, Liquid; D006801:Humans; D013058:Mass Spectrometry; D008676:Metanephrine / Q000097:blood*; D008875:Middle Aged; D009647:Normetanephrine / Q000097:blood*; D010673:Pheochromocytoma / Q000097:blood / Q000175:diagnosis*; D010949:Plasma; D012016:Reference Values; D012680:Sensitivity and Specificity
chemical_list: D009647:Normetanephrine; D008676:Metanephrine