Reference measurements of cadmium and lead contents in candidates for new environmental certified materials by isotope dilution inductively coupled plasma mass spectrometry

The analytical procedures for the reference measurements of cadmium and lead concentrations in four candidates for new environmental certified reference materials were developed. Cadmium and lead content was determined in bottom sediment (M-2 BotSed), Baltic herring tissue (M-3 HerTis), cormorant tissue (M-4 CormTis) and codfish tissue (M-5 CodTis). The measurements were carried out with the use of a direct isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS). The isotope dilution approach and the combined uncertainty of results are based on the mathematical equations as from definition of a primary method of measurement. All factors influencing the final results included: the procedural blank, the moisture content in the materials, the factors affecting the blend ratio measurements (instrumental background, spectral interferences, dead time, mass discrimination effects and the repeatability of measured isotopic ratios) as well as the isotopic equilibrium were systematically investigated and included in the uncertainty budget. The content of cadmium in candidates for new environmental reference materials, after correction for moisture contents, matrix separation on ion-exchange resin AG1-X8 of the blended samples and after using for the ICP-MS measurements ratio of pair of isotopes n(110Cd)/n(111Cd) was found to be: (2.18 ± 0.06) μg g−1 in M-2 BotSed, (337 ± 2) ng g−1 in HerTis, (16.4 ± 0.6) ng g−1 in CormTis) and (2.7 ± 0.4) ng g−1 in CodTis, respectively. The content of lead in candidates for new environmental reference materials, after correction for moisture contents, matrix separation on ion-exchange resin AG1-X8 of the blended samples and after using for the ICP-MS measurements ratio of pair of isotopes n(208Pb)/n(207Pb) was found to be: (108 ± 5) ng g−1 in M-3 HerTis, (2.34 ± 0.12) μg g−1 in M-4 CormTis and (43 ± 2) ng g−1 in M-5 CodTis, respectively. The Cd and Pb contents determined in this work were used as a contribution of the Faculty of Chemistry, Biological and Chemical Research Centre University of Warsaw in the characterisation of the abovementioned candidates for new certified reference materials in the frame of the Inter-Laboratory Comparison, organized by the Institute Nuclear Chemistry and Technology (Warsaw, Poland). The obtained excellent agreement within uncertainties with the reference values further validated the methods developed in this study.