Simultaneous Determination of Cd, In, Tl and Bi by Isotope Dilution-Internal Standardisation ICP-QMS with Corrections Using Externally Measured MoO⁺/Mo⁺ Ratios

A method for the simultaneous determination of Cd with In, Tl and Bi by isotope dilution-internal standardisation (ID-IS) ICP-QMS using the same aliquot for rare earth element and other trace element determinations was developed. Samples mixed with an enriched ¹⁴⁹Sm spike were decomposed using a HF-HClO₄ mixture, which was evaporated and then diluted with HNO₃. After determination of Sm by ID-ICP-QMS and Cd, In, Tl and Bi concentrations were determined using the ¹⁴⁹Sm intensity as an internal standard. The interference of MoO⁺ on Cd⁺ was corrected using the MoO⁺/Mo⁺ ratio separately measured using a Mo standard solution, and the validity of the externally determined oxide-forming ratio correction was evaluated. The MoO⁺/Mo⁺ ratios measured using the standard solution and samples were ∼ 0.0002 and <0.002, respectively. Detection limits for Cd, In, Tl and Bi in silicate samples were at levels of <1ngg^-1 with a total uncertainty of <7%. Cadmium in the carbonaceous chondrites, Orgueil (CI1), Murchison (CM2) and Allende (CV3) as well as Cd, In, Tl and Bi in the reference materials, JB-2, JB-3, JA-1, JA-2, JA-3, JP-1 (GSJ), BHVO-1, AGV-1, PCC-1 and DTS-1 (USGS) and NIST SRM 610, 612, 614 and 616 were determined to show the applicability of this method.