Determination of total Hg isotopic composition at ultra-trace levels by on line cold vapor generation and dual gold-amalgamation coupled to MC-ICP-MS

Abstract

An online pre-concentration method was developed to directly determine Hg isotopic compositions at the ng L⁻¹ level in liquid samples. It is based on the hyphenation of a commercially available cold vapor generation dual gold amalgamation system to a multi-collector ICP-MS. This automated method supports a rapid throughput and consumes less than 100 mL of sample (20–90 mL), representing a decrease of the sample size of more than two orders of magnitude in comparison to existing off-line pre-concentration strategies. The accuracy and the precision were evaluated by the analysis of a secondary standard (UM Almadén) and results for a Hg concentration of 5 ng L⁻¹ were δ²⁰²Hg = −0.55 ± 0.26‰ and Δ¹⁹⁹Hg = −0.02 ± 0.15‰ (±2SD, n = 14). The method has been compared to the actual reference technique with the analysis of 6 environmental reference materials. Direct on line cold vapor generation and dual gold-amalgamation coupled to MC-ICP-MS demonstrates its relevant applicability for low Hg concentrated environmental samples (undersized biological samples, natural waters).