CCQM-K161 "Anions in Seawater"

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Main textAnions or nutrients in seawater are very important targets for oceanographic research and environmental monitoring of contaminations. Quantification of minor and trace anions in seawater has always been a challenge for the extremely high salinity, disparate levels of analyte and matrix ions, and even need to be measured at levels close to the detection limits of the method performance. Evidence of successful participation in formal, relevant international comparisons is needed to support calibration and measurement capability claims (CMCs) made by the national metrology institutes (NMIs) and designated institutes (DIs).The CCQM-K161 Anions in Seawater was organized by the Inorganic Analysis Working Group (IAWG) of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) to assess the abilities of the NMIs and DIs for the accurate determination of minor and trace anions in seawater. The measurands covered chloride (16 mg/g-25 mg/g), sulfate (1 mg/g-4 mg/g), bromide (30 mg/kg-100 mg/kg), nitrate (1 mg/kg-5 mg/kg) and phosphate (60 µg/kg-300 µg/kg). Twelve national metrology institutes and designated institutes participated in this key comparison. Participants were requested to evaluate the mass fractions, expressed in mg/g for chloride and sulfate, mg/kg for bromide and nitrate, and µg/kg for phosphate (as phosphorus) in a mixed natural seawater that was spiked with the phosphate. A variety of techniques including isotope dilution inductively coupled plasma mass spectrometry (IDMS), isotope dilution gas chromatography-mass spectrometry (ID-GC-MS), ion chromatography (IC), UV visible spectrophotometry (UV-Vis), flow injection analysis (FIA) was used by the participants for the determination.The NIST Decision Tree was used to assign the KCRV estimate and to calculate the degrees of equivalence of each participants following the IAWG Guidance on Using NIST Decision Tree for Comparison Reporting from 30 June 2023.Successful participation in CCQM-K161 demonstrates measurement capabilities for determination of anions in seawater. Considering the IAWG Core Capability Matrix, this material falls into the matrix challenge called 'High salts content', which corresponds to the CCQM amount-of-substance category sea water, and so will support CMCs for the anions in a mass fraction range from 60 µg/kg to 25 mg/g.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).