Sensitive Cd isotopic analysis by multi-collector inductively coupled plasma mass spectrometry using electrothermal vaporization.

Abstract

A fast and highly sensitive method for cadmium (Cd) isotopic analysis was developed by coupling electrothermal vaporization (ETV) with multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS). In this approach, a 5 μL Cd sample was dropped onto the W-coil ETV, followed by sequential drying and vaporization. The vaporized analyte was then swept into the MC-ICPMS for isotopic analysis, and the whole analysis process took only 3 min. This system exhibited exceptional sampling efficiency, achieving > 99% Cd vaporization and reducing sample consumption to only 2 ng per analysis, representing a 20-fold improvement over conventional pneumatic nebulization (PN). The ETV transient signals were recorded in time resolved analysis (TRA) mode, and the isotope ratio processing was calculated using the linear regression slope (LRS) method. These ratios were further corrected for instrumental mass bias using a combination of double spike (DS) and standard-sample bracketing (SSB), ensuring high precision and accuracy. Repeated analyses of NIST 3108 and GBW 08612 (in-house standard) yielded δ^114/110Cd values of 0.00 ± 0.05‰ (2SD, n = 12) and - 0.96 ± 0.05‰ (2SD, n = 12), respectively. Tests on standard samples purified once and twice showed no significant differences, indicating better matrix tolerance over the conventional PN method. This method enables high-throughput Cd isotopic analysis of trace-level environmental samples, facilitating investigations into biogeochemical cycling at low Cd concentrations and pollution source tracing.