title: Candidate reference measurement procedures for chloride, potassium, sodium, calcium, magnesium, and lithium by inductively coupled plasma (isotope dilution) sector field mass spectrometry (ICP-(ID) SFMS) in serum.
abstract: BACKGROUND
  Standardization of the measurement of electrolyte concentrations in serum is of considerable interest for quality assurance in patient care. To promote the ongoing process of standardization we developed candidate reference measurement procedures of highest metrological order for Cl, K, Na, Ca, Mg, and Li using ICP-(ID) SFMS.
  
  
  METHODS
  Serum samples were diluted with 4 mmol/L nitric acid and were spiked with the internal standard for quantification, separately for each analyte. The samples were introduced in the ICP-SFMS device by continuous infusion using a peristaltic pump. The measurement results were compared with reference measurement procedure values obtained by atom absorption spectroscopy, flame emission spectroscopy, and coulometry. The measurement accuracy and precision was calculated by analyzing certified reference materials and EQAS samples.
  
  
  RESULTS
  The mean coefficient of variation (CV) of the ICP-MS procedures for the serum samples was 0.65% for Cl, 0.46% for K, 0.51% for Na, 0.77% for Ca, 0.78% for Mg, and 0.58% for Li. The mean bias from target values of NIST certified reference materials was +0.85% for Cl, -0.46% for K, +0.68% for Na, -0.21% for Ca, +0.27% for Mg, and -0.39% for Li.
  
  
  CONCLUSIONS
  Candidate reference measurement procedures for 6 electrolytes were developed by high performance magnetic sector field ICP-MS fulfilling the requirements of ISO 15193:2009 for reference measurement procedures with traceability to SI according to ISO 17511:2003 and can be used for setting target values in EQAS and for certification of reference materials.
authors.affiliation: Reference Laboratory, Instand e.V., Düsseldorf, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Kramer
authors.forename: M
authors.initials: M
authors.lastname: Kress
authors.forename: H
authors.initials: H
authors.lastname: Reinauer
authors.forename: M
authors.initials: M
authors.lastname: Spannagl
authors.forename: P
authors.initials: P
authors.lastname: Kaiser
mesh_terms: D002118:Calcium / Q000097:blood / Q000592:standards; D002712:Chlorides / Q000097:blood / Q000592:standards; D006801:Humans; D007201:Indicator Dilution Techniques; D008094:Lithium / Q000097:blood / Q000592:standards; D008274:Magnesium / Q000097:blood / Q000592:standards; D013058:Mass Spectrometry / Q000379:methods*; D008670:Metals / Q000097:blood* / Q000592:standards; D011188:Potassium / Q000097:blood / Q000592:standards; D012015:Reference Standards; D012964:Sodium / Q000097:blood / Q000592:standards
chemical_list: D002712:Chlorides; D008670:Metals; D008094:Lithium; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium