Cadmium isotopic composition of biogenic certified reference materials determined by thermal ionization mass...

A¹¹⁶Cd-¹⁰⁶Cd double-spike method in combination with thermal ionization mass spectrometry (TIMS) was applied to obtain cadmium (Cd) mass fractions and stable isotope compositions in seven biogenic certified reference materials (pine needles, tomato leaves, spinach leaves, lichen, mussel tissue, oyster tissue, and pig kidney). This sample set was supplemented by the analysis of two manganese nodules and one soil reference material for which the Cd isotopic data has already been reported. The intermediate measurement precision of the whole protocol as determined for the NIST SRM 3108 Cd standard solution yields an excellent value of δ^114/110Cd of -0.005 ± 0.029‰ (2SD, n = 47). The Cd isotopic compositions of the biogenic materials, reported as δ^114/110Cd relative to NIST SRM 3108, range from -0.52 to +0.50‰. Plants show δ^114/110Cd mean values ranging from -0.09 to +0.45‰ whereas the δ^114/110Cd value of -0.17‰ was detected in the lichen and the values of -0.51, -0.52, and +0.47‰ were gathered for the oyster, mussel, and pig kidney tissues, respectively. The observed large variation of the δ^114/110Cd values in the biogenic reference materials indicates a potential to use the natural mass-dependent Cd isotope fractionation in environmental, biogeochemical, and physiological studies.