title: Determination of cortisol production rates with contemporary liquid chromatography-mass spectrometry to measure cortisol-d(3) dilution after infusion of deuterated tracer.
abstract: OBJECTIVE
  Measurement of 24-h cortisol production rate (CPR) using steady-state infusion of deuterated cortisol and analysis of stable-isotope dilution by MS is a valuable tool to examine hypothalamic-pituitary-adrenal axis activity in humans. We have developed and validated an improved method for measuring cortisol dilution with contemporary LC-MS technology.
  
  
  METHODS
  Plasma samples and calibrators were extracted with ethylacetate. LC-MS was performed with a Surveyor HPLC and TSQ Quantum triple-quadrupole mass spectrometer equipped with an atmospheric pressure chemical ionization (APCI) source.
  
  
  RESULTS
  Selectivity was improved over previous methods via elimination of an interferent identified as 20β-dihydrocortisol. The LLOQ for cortisol-d(3) was 2.73nmol/L and LOD 1.37nmol/L. Plasma calibrators were linear over the concentration range 1.5-10% cortisol-d(3), with correlation coefficients >0.995.
  
  
  CONCLUSIONS
  This APCI LC-MS method offers simplified sample work-up and analysis and enables selective detection of the low concentration of cortisol-d(3) infused for determination of 24-h CPR.
authors.affiliation: Division of Endocrinology, Diabetes, and Clinical Nutrition, Oregon Health & Science University, Portland, OR 97201, USA.
authors.forename: Bethany J
authors.initials: BJ
authors.lastname: Klopfenstein
authors.forename: Jonathan Q
authors.initials: JQ
authors.lastname: Purnell
authors.forename: David D
authors.initials: DD
authors.lastname: Brandon
authors.forename: Lorne M
authors.initials: LM
authors.lastname: Isabelle
authors.forename: Andrea E
authors.initials: AE
authors.lastname: DeBarber
mesh_terms: D002138:Calibration; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003903:Deuterium; D006801:Humans; D006854:Hydrocortisone / Q000096:biosynthesis*; D057230:Limit of Detection; D013058:Mass Spectrometry / Q000379:methods*
chemical_list: D003903:Deuterium; D006854:Hydrocortisone