High-Precision Cd Isotope Measurements of Soil and Rock Reference Materials by MC-ICP-MS with Double Spike Correction

This study presents a high-precision Cd isotope measurement method for soil and rock reference materials using MC-ICP-MS with double spike correction. The effects of molecular interferences (e.g., (AgH+)-Ag-109-H-1, (ZrO+)-Zr-94-O-16, (MoO+)-Mo-94-O-16 and (ZnAr+)-Zn-70-Ar-40) and isobaric interferences (e.g., Pd, In and Sn) to Cd isotope measurements were quantitatively evaluated. When the measured solution has Ag/Cd <= 5, Zn/Cd <= 0.02, Mo/Cd <= 0.4, Zr/Cd <= 0.001, Pd/Cd <= 5 x 10(-5) and In/Cd <= 10(-3), the measured Cd isotope data were not significantly affected. The intermediate measurement precision of pure Cd solutions (BAM I012 Cd, Munster Cd and AAS Cd) was better than +/- 0.05 parts per thousand (2s) for delta Cd-114/110. The delta Cd-114/110 values of soil reference materials (NIST SRM 2709, 2709a, 2710, 2710a, 2711, 2711a and GSS-1) relative to NIST SRM 3108 were in the range of -0.251 to 0.632 parts per thousand, the delta Cd-114/110 values of rock reference materials (BCR-2, BIR-1, BHVO-2, W-2, AGV-2, GSP-2 and COQ-1) varied from -0.196 parts per thousand to 0.098 parts per thousand, and that of the manganese nodule (NOD-P-1) was 0.163 +/- 0.040 parts per thousand (2s, n = 8). The large variation in Cd isotopes in soils and igneous rocks indicates that they can be more widely used to study magmatic and supergene processes.