title: Comparison by LC-MS and MALDI-MS of prostate-specific antigen from five commercial sources with certified reference material 613.
abstract: OBJECTIVE
  Prostate-specific antigen (PSA) samples from five commercial sources were compared with PSA from the European Commission Community Bureau of Reference, known as CRM 613, using liquid chromatography-mass spectrometry (LC-MS) and matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS).
  
  
  METHODS
  The effects of storage at various temperatures, multiple freeze-thaw cycles and lyophilization vs. solution storage were investigated.
  
  
  RESULTS
  : CRM 613 and the five commercially available samples varied in their heterogeneity and in the amount of PSA with a molecular mass of 28,430 kDa. Few changes were observed among any of the samples during the stability study or study of the effect of lyophilization and freeze-thaw cycles.
  
  
  CONCLUSIONS
  Use of many of the commercial PSA sources as authentic PSA standards for calibrants for in vitro diagnostic tests could lead to significantly biased PSA measurements. Although all the PSA samples appear to be relatively stable for the time periods and conditions studied, some of the commercially available samples contain limited amounts of PSA and included other unidentified components.
authors.affiliation: National Institute of Standards and Technology, Analytical Chemistry Division, Gaithersburg, MD 20899-0001, USA. mary-satterfield@nist.gov
authors.forename: Mary B
authors.initials: MB
authors.lastname: Satterfield
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Welch
mesh_terms: D002851:Chromatography, High Pressure Liquid; D015925:Cryopreservation; D005612:Freeze Drying; D006801:Humans; D017430:Prostate-Specific Antigen / Q000032:analysis / Q000592:standards*; D012015:Reference Standards; D012996:Solutions; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013696:Temperature
chemical_list: D012996:Solutions; D017430:Prostate-Specific Antigen