title: Determination of serum aldosterone by liquid chromatography and tandem mass spectrometry: a liquid-liquid extraction method for the ABSCIEX API-5000 mass spectrometry system.
abstract: OBJECTIVE
  Accurate serum aldosterone determination is critical to the screening and diagnosis of primary aldosteronism, the localisation of aldosterone producing tumours, and the investigation of other disorders of the renin-angiotensin system. Mass spectrometry offers a means to overcome problems with method-dependent bias between competitive immunoassays for aldosterone. The authors have developed a simple, sensitive and precise liquid-liquid extraction aldosterone method for the ABSCIEX API-5000 liquid chromatography and tandem mass spectrometry (LC-MS/MS) system.
  
  
  METHODS
  Using d7-aldosterone internal standard, 500 μl of sample is extracted with 2500 μl of methyl tertbutyl ether followed by dry-down, reconstitution and LC-MS/MS analysis in ESI negative mode. Method validation was undertaken using standard approaches and comparison made against a commercial radioimmunoassay. Accuracy was assessed using EQA material with assigned aldosterone concentrations.
  
  
  RESULTS
  The assay was linear up to 3420 pmol/l (LOQ=50 pmol/l, LOD<22 pmol/l). Total CVs were ≤5% for concentrations ≥120 pmol/l and 10% at the LOQ. Mean accuracy was 98.5% against GCMS assigned material.
  
  
  CONCLUSIONS
  The authors present a precise, sensitive and simple aldosterone method suitable for routine clinical use that requires no solid phase extraction or specialised ion sources.
authors.affiliation: St. Paul's Hospital, Department of Pathology and Laboratory Medicine, Vancouver, British Columbia, Canada.
authors.forename: Jessica Grace
authors.initials: JG
authors.lastname: Van Der Gugten
authors.forename: Joshua
authors.initials: J
authors.lastname: Dubland
authors.forename: Hua-Fen
authors.initials: HF
authors.lastname: Liu
authors.forename: Alex
authors.initials: A
authors.lastname: Wang
authors.forename: Christine
authors.initials: C
authors.lastname: Joseph
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Holmes
mesh_terms: D000450:Aldosterone / Q000097:blood*; D002138:Calibration; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D006929:Hyperaldosteronism / Q000097:blood / Q000175:diagnosis; D059625:Liquid-Liquid Extraction / Q000379:methods*; D011863:Radioimmunoassay; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D000450:Aldosterone