title: On the isobaric space of 25-hydroxyvitamin D in human serum: potential for interferences in liquid chromatography/tandem mass spectrometry, systematic errors and accuracy issues.
abstract: BACKGROUND
  Isobaric interferences in human serum can potentially influence the measured concentration levels of 25-hydroxyvitamin D [25(OH)D], when low resolving power liquid chromatography/tandem mass spectrometry (LC/MS/MS) instruments and non-specific MS/MS product ions are employed for analysis. In this study, we provide a detailed characterization of these interferences and a technical solution to reduce the associated systematic errors.
  
  
  METHODS
  Detailed electrospray ionization Fourier transform ion cyclotron resonance (FTICR) high-resolution mass spectrometry (HRMS) experiments were used to characterize co-extracted isobaric components of 25(OH)D from human serum. Differential ion mobility spectrometry (DMS), as a gas-phase ion filter, was implemented on a triple quadrupole mass spectrometer for separation of the isobars.
  
  
  RESULTS
  HRMS revealed the presence of multiple isobaric compounds in extracts of human serum for different sample preparation methods. Several of these isobars had the potential to increase the peak areas measured for 25(OH)D on low-resolution MS instruments. A major isobaric component was identified as pentaerythritol oleate, a technical lubricant, which was probably an artifact from the analytical instrumentation. DMS was able to remove several of these isobars prior to MS/MS, when implemented on the low-resolution triple quadrupole mass spectrometer.
  
  
  CONCLUSIONS
  It was shown in this proof-of-concept study that DMS-MS has the potential to significantly decrease systematic errors, and thus improve accuracy of vitamin D measurements using LC/MS/MS.
authors.affiliation: Institute of Bioanalytical Chemistry, Saarland University, D-66123, Saarbrücken, Germany.
authors.forename: Yulin
authors.initials: Y
authors.lastname: Qi
authors.forename: Timon
authors.initials: T
authors.lastname: Geib
authors.forename: Pascal
authors.initials: P
authors.lastname: Schorr
authors.forename: Florian
authors.initials: F
authors.lastname: Meier
authors.forename: Dietrich A
authors.initials: DA
authors.lastname: Volmer
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods*; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood / Q000737:chemistry
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D