title: Matrix effect explained by unexpected formation of peptide in acidified plasma.
abstract: OBJECTIVE
  Peak distortion and strong signal enhancement was observed when applying a bioanalytical method based on mixed-mode SPE, hydrophilic interaction chromatography and ESI-MS to acidified rabbit plasma samples.
  
  
  RESULTS
  High-resolution ESI-MS and N-terminal peptide sequencing revealed a peptide NFQNAL, which was confirmed by H/D exchange ESI-MS.
  
  
  CONCLUSIONS
  The peptide causing the observed matrix effect was formed by enzymatic degradation of serum albumin at pH 3. Degradation required both acidification and presence of other plasma constituents in addition to albumin to take place. The degree of signal enhancement correlated to the level of NFQNAL in the ion source as measured by MS, with a maximal enhancement factor of 3 at intermediate levels of NFQNAL. The interference was eliminated by changing to another type of hydrophilic interaction chromatography column.
authors.affiliation: Department of Chemistry & Molecular Biology, University of Gothenburg, SE-412 96 Gothenburg, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Ahnoff
authors.forename: Ann-Christin
authors.initials: AC
authors.lastname: Nyström
authors.forename: Fritz
authors.initials: F
authors.lastname: Schweikart
authors.forename: Anja
authors.initials: A
authors.lastname: Ekdahl
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016477:Artifacts; D001774:Blood Chemical Analysis / Q000379:methods*; D002417:Cattle; D041961:Deuterium Exchange Measurement; D006801:Humans; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D051379:Mice; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000097:blood* / Q000737:chemistry / Q000378:metabolism; D059748:Proteolysis; D011817:Rabbits; D012709:Serum Albumin / Q000737:chemistry / Q000378:metabolism; D052616:Solid Phase Extraction; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D009842:Oligopeptides; D012709:Serum Albumin