Development and Co-Validation of a Certified Reference Material (NMIJ CRM 7204-A) for the Analysis of Trace Elements in Seawater Sample

A certified reference material (CRM), i.e. NMIJ CRM 7204-a, was characterized for the analysis of 10 regulated trace elements in sample seawater, provided in 500 mL polyethylene bottles. Homogeneity and stability of the elements were investigated by inductively coupled plasma tandem quadrupole mass spectrometry after proper dilution, while mass-shift mode was applied to the measurement of trace elements except for Cd and Pb. A property value was obtained as the weighted mean of the results obtained by different methods with weights based on the reciprocal of the standard uncertainty. Combined uncertainty of a property value was obtained as the root mean square of the standard uncertainties of homogeneity, stability, analysis reproducibility, method-to-method variance, and calibrating standard. In NMIJ CRM 7204-a, the concentration of Cd is approximately 3 µg/kg, while those of other trace elements are around 10 µg/kg. Validity of the certified values was confirmed with analytical results of As and Cd by National Institute of Metrology (NIM, China) and those of Cd and Ni by Korea Research Institute of Standards and Science (KRISS, Korea). The concentrations of Na, Mg, K, and Ca along with the density values at 15, 20, and 25 Celsius were provided as information values.