title: Predicted influence of sample hematocrit on injected mass of internal standard in mass spectrometry assays utilizing simple protein precipitation for sample preparation.
abstract: BACKGROUND
  The injected mass of internal standard is often monitored in mass spectrometry assays to flag aberrant specimen processing. When simple protein precipitation is used for sample preparation, the protein volume (solids fraction) of the specimen is in principle a variable affecting the final concentration of the internal standard in the liquid phase. We examined the predicted extent of this variation for an example of protein precipitation for sample preparation used in a mass spectrometry assay for immunosuppressants in whole blood.
  
  
  METHODS
  Liquid and solid mass fractions of samples with hematocrit ranging from 15% to 60% were measured after protein precipitation of samples using a whole blood/precipitating reagent ratio of 1:4. Relative supernatant volumes as a function of hematocrit were determined.
  
  
  RESULTS
  Liquid volume variation was consistent with a predicted variation in the internal standard concentration of only approximately +/-1% across this hematocrit range. Data were in close agreement with calculations based simply on protein density and concentration.
  
  
  CONCLUSIONS
  Hematocrit affects the injected mass of internal standard in assays that utilize protein precipitation for sample preparation, due to predictable variation in solids and liquid fractions. The effect is small, however, compared to the typical variation observed for injected mass of internal standard.
authors.affiliation: Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE 68198-3135, USA.
authors.forename: Allison M
authors.initials: AM
authors.lastname: Cushman-Vokoun
authors.forename: Kim B
authors.initials: KB
authors.lastname: Plath
authors.forename: James D
authors.initials: JD
authors.lastname: Landmark
authors.forename: Douglas F
authors.initials: DF
authors.lastname: Stickle
mesh_terms: D000818:Animals; D011232:Chemical Precipitation; D006400:Hematocrit; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods / Q000592:standards*; D011506:Proteins / Q000737:chemistry*; D012015:Reference Standards; D015203:Reproducibility of Results
chemical_list: D011506:Proteins