Cadmium Isotope Analysis Of Environmental Reference Materials Via Microwave Digestion–Resin Purification–Double-Spike MC-ICP-MS

Cadmium isotope fractionation is a promising indicator for tracing the source, transport, and transformation of Cd in the environment; therefore, a high-precision method for the Cd isotope analysis of environmental samples is urgently required. In this study, eight environmental reference materials (NIST 2711a, GSS-1, GSS-4, GSS-5, GSD-11, GSD-12, GSD-30, and BCR679) with different matrices were digested under microwave irradiation and purified via anion exchange. Thereafter, their Cd isotope ratios were analyzed using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) with double-spike correction. The samples digested under microwave irradiation exhibited high Cd recovery (> 96%). One step of anion-exchangebased purification can remove most interfering elements without any detectable loss of Cd. If the purified solution contained Zn/Cd > 0.04, Zr/Cd > 0.01, Mo/Cd > 0.2, Pd/Cd > 4 × 10, In/Cd > 0.02, or Sn/Cd > 0.1, a secondary step using the same purification procedure would be necessary. The measured δCd values of reference materials (from −0.558 to 0.550‰) were in adequate agreement with those of previous studies, suggesting that this method can be used to analyze the Cd isotope ratios in soil, sediment, and plant samples. In addition, the large variation in the Cd isotope ratios of these reference materials implies that the Cd isotope ratio is promising for identifying pollution sources and the biogeochemical cycle of Cd.