Fast and highly sensitive Cd isotopic analyses in low-Cd complex samples with MC-ICPMS based on plasma electrochemical vapor generation

Abstract

Cd isotopes have provided a powerful tool for better understanding Cd geochemical cycling in soil, water and biological systems. Conventional solution-based MC-ICPMS techniques used for Cd isotopic analysis typically requires time-consuming purification, which greatly limits the wide application of Cd isotope. In this work, a fast, highly sensitive and cost-effective Cd isotopic analysis method has been developed based on plasma electrochemical vapor generation (PEVG) coupled with MC-ICPMS. PEVG enhances sensitivity by more than 6 times compared with conventional pneumatic nebulization (PN) system, allowing Cd analysis to be carried out with samples as low as ∼ 13 ng. Usefully, the tolerance level for organic resin materials and matrix elements (Sn/In/Pd/Zr/Mo/Zn:Cd > 250:1) is greatly improved because of the excellent matrix separation capability inherent to PEVG. This allows simplification of the complex and time-consuming ion-exchange chromatography purification process, achieving a reduction of time by > 20 times compared to conventional two-step Cd purification process. The precision and accuracy of this method were first assessed by measuring NIST 3108 and BGEG-Cd standard under optimum conditions (δ114/110Cd of 0.00 ± 0.06‰ and −1.00 ± 0.06‰ (2sd, n = 25)). The method was also successfully applied to sensitive and fast determination of δ114/110Cd in various reference materials (soil, sediment, and basalt) and environmental samples (pyrite, galena, sphalerite, soils and tap water), validating the applicability of the proposed technique. Owing to the sensitivity, selectivity, low power, and low gas consumption of the PEVG, the proposed PEVG-MC-ICPMS technique provides a much faster and cost-effective approach for the accurate measurement of Cd isotopic compositions in low-Cd complex samples.