title: Improved plasma free metadrenaline analysis requires mixed mode cation exchange solid-phase extraction prior to liquid chromatography tandem mass spectrometry detection.
abstract: BACKGROUND
  The investigation and effective management of phaeochromocytoma involves biochemical measurement of either conjugated total urine or plasma free metadrenalines. Current analytical methods include enzyme-linked immunosorbent assays, high-performance liquid chromatography (HPLC) with electrochemical detection (ECD) or liquid chromatography tandem mass spectrometry (LCMS/MS). Since the first two methods are either extremely laborious, necessitate low sample run numbers, result in slow turnaround times or are subject to analytical interference, a robust, routine clinical method is not achievable. We established a novel sample preparation method to measure plasma free metadrenalines using LCMS/MS.
  
  
  METHODS
  Three different solid-phase extraction (SPE) methods were compared: hydrophilic-lipophilic balance sorbent (HLB), weak cation exchange (WCX) and mixed mode cation exchange (MCX) and their ability to remove interfering compounds prior to LCMS/MS analysis. Maximum recovery of plasma free metadrenaline and plasma free normetadrenaline were achieved by positively charging compounds prior to SPE application.
  
  
  RESULTS
  Compared with HLB and WCX cartridges, MCX extraction resulted in chromatography without co-eluting interference with superior assay precision and accuracy. Additionally, samples that could not be quantified because of interference using HPLC/ECD could be readily assayed using this new method.
  
  
  CONCLUSIONS
  The use of the MCX SPE method with LCMS/MS detection provides an improved assay to measure plasma free metadrenalines in comparison to many available alternative methods.
authors.affiliation: Department of Core Clinical Pathology and Biochemistry, Royal Perth Hospital, Perth, Western Australia, Australia. michael.clarke@uwa.edu.au
authors.forename: Michael W
authors.initials: MW
authors.lastname: Clarke
authors.forename: Brian
authors.initials: B
authors.lastname: Cooke
authors.forename: Kirsten
authors.initials: K
authors.lastname: Hoad
authors.forename: Paul
authors.initials: P
authors.lastname: Glendenning
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000097:blood / Q000175:diagnosis*; D053000:Analytic Sample Preparation Methods; D002411:Cation Exchange Resins / Q000737:chemistry; D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D008676:Metanephrine / Q000097:blood*; D009647:Normetanephrine / Q000097:blood; D010673:Pheochromocytoma / Q000097:blood / Q000175:diagnosis*; D052617:Solid Phase Microextraction / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D002411:Cation Exchange Resins; D009647:Normetanephrine; D008676:Metanephrine