Measuring Hg Isotopes in Bio‐Geo‐Environmental Reference Materials

Abstract

With the emergence of new analytical techniques and the expansion of scientific fields explored by using mercury isotopes, the community needs reference materials (RM) to validate and assure the accuracy of the results. The present work investigates (1) the characterisation of secondary RM in order to validate analytical systems, (2) the effects of two complex matrices on isotopic determination using stannous chloride cold vapour generation coupled to MC‐ICP‐MS (CV‐MC‐ICP‐MS), (3) the effects of multiple digestion techniques for total Hg extraction and (4) the characterisation of nine geo‐bio‐environmental RM. Two secondary mono‐elemental RMs analysed using two different analytical setups yielded isotopic compositions on δ202Hg of −3.54 ± 0.27‰ (CRPG‐F65A, 2SD, n = 38) and +2.59 ± 0.19‰ (CRPG‐RL24H, 2SD, n = 30) relative to the CRM NIST SRM 3133. These two RMs cover the whole range of Hg isotopic fractionation in natural samples and are made available to the scientific community. Complex fly ash and hydroxysulfate green rust matrices were synthesised, spiked with NIST SRM 3133, then digested and finally analysed versus the mono‐elemental NIST SRM 3133 to show potential effect of these complex matrices during CV‐MC‐ICP‐MS. Three digestions techniques, including traditional acid digestion, microwave digestion and high pressure‐high temperature digestion, were applied to the lichen RM BCR‐482 in order to compare advantages and drawbacks of these methods. Finally, the isotopic compositions of nine RMs including soils (NIST SRM 2711; GXR‐2; GSS‐4), sediment (GSD‐10), jasperoid (GXR‐1), ore deposit (GXR‐3), fly ashes (BCR‐176; BCR‐176R) and lichen (BCR‐482) are reported. These selected materials have δ202Hg values ranging from −1.75‰ to +0.11‰. Some RMs also presented mass‐independent fractionation with Δ199Hg and Δ201Hg of up to −0.6‰.