Certification of trace metals in seawater certified reference materials (CRMs) NASS-7 and CASS-6 is described. At the National Research Council Canada (NRC), column separation was performed to remove the seawater matrix prior to the determination of Cd, Cr, Cu, Fe, Pb, Mn, Mo, Ni, U, V, and Zn, whereas As was directly measured in 10-fold diluted seawater samples, and B was directly measured in 200-fold diluted seawater samples. High-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) was used for elemental analyses, with double isotope dilution for the accurate determination of B, Cd, Cr, Cu, Fe, Pb, Mo, Ni, U, and Zn in seawater NASS-7 and CASS-6, and standard addition calibration for As, Co, Mn, and V. In addition, all analytes were measured using standard addition calibration with triple quadrupole (QQQ)-ICPMS to provide a second set of data at NRC. Expert laboratories worldwide were invited to contribute data to the certification of trace metals in NASS-7 and CASS-6. Various analytical methods were employed by participants including column separation, co-precipitation, and simple dilution coupled to ICPMS detection or flow injection analysis coupled to chemiluminescence detection, with use of double isotope dilution calibration, matrix matching external calibration, and standard addition calibration. Results presented in this study show that majority of laboratories have demonstrated their measurement capabilities for the accurate determination of trace metals in seawater. As a result of this comparison, certified/reference values and associated uncertainties were assigned for 14 elements in seawater CRMs NASS-7 and CASS-6, suitable for the validation of methods used for seawater analysis.

CFOS IARC University of Alaska Fairbanks Fairbanks AK 99775 7220 USA

Department of Chemistry and Industrial Chemistry University of Genoa Via Dodecaneso 31 16146 Genoa Italy

GEOMAR Helmholtz Centre for Ocean Research Wischhofstr 1 3 24148 Kiel Germany

Institute for Chemical Research Kyoto University Gokasho Uji city Kyoto 611 0011 Japan

Institute for Marine Antarctic Studies University of Tasmania 20 Castray Esplanade Battery Point Hobart TAS 7004 Australia

Institute for the Dynamics of Environmental Processes National Research Council of Italy Italy

Institute of Analytical Chemistry of the Czech Academy of Sciences Veveří 97 602 00 Brno Czech Republic

Laboratoire des sciences de l'Environnement MARin UMR CNRS UBO IRD Ifremer 6539 Place Nicolas Copernic Technopôle Brest Iroise 29280 Plouzané France

National Research Council Canada 1200 Montreal Rd Ottawa Ontario K1A 0R6 Canada

QUASIMEME NL 6700 EC Wageningen Bornsesteeg 10 Bennekom 6721 NG Ede The Netherlands

Research School of Earth Sciences The Australian National University Canberra ACT 2601 Australia

Rosenstiel School of Marine and Atmospheric Science 4600 Rickenbacker Causeway Miami FL 33149 USA

School of Biology and Marine sciences Shenzhen University Shenzhen 518060 Guangdong China

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