HR: 1340h
AN: B13A-0884 INVITED    [Abstracts]
TI: Reporting and measurement of mass-dependent and mass-independent fractionation of mercury isotopes
AU: * Bergquist, B A
EM: bbergqui@umich.edu
AF: University of Michigan, Department of Geological Sciences 1100 N. University Ave 2534 C.C. Little, Ann Arbor, MI 48109, United States
AU: Blum, J D
EM: jdblum@umich.edu
AF: University of Michigan, Department of Geological Sciences 1100 N. University Ave 2534 C.C. Little, Ann Arbor, MI 48109, United States
AB: Hg isotope analysis by MC-ICP-MS is an important new approach for fingerprinting Hg sources and monitoring Hg redox reactions and bioaccumulation, especially with the recent discovery of mass independent Hg isotope fractionation. Unfortunately research groups have adopted different standards, definitions of delta values, and methods of isotopic measurement. We suggest that a single standard, NIST SRM 3133, be adopted for reporting the isotopic variability of Hg isotopes. Isotope ratios should be determined by sample-standard bracketing (SSB) during analysis and reported as permil (‰) deviation from SRM 3133. For the highest precision and accuracy, a Tl internal standard along with SSB should be used to correct instrumental mass bias. Measurement routines should also include on-peak zero corrections and matching of concentration and matrix between the samples and bracketing standard. For samples that display mass-dependent fractionation (MDF), only one delta value needs to be reported (δ^202/198Hg). Mass-independent fractionation (MIF) (Jackson et al., 2006; Bergquist et al., 2006; Bergquist and Blum, submitted) requires additional nomenclature, and we suggest reporting MIF as the deviation in isotope ratios from the theoretical mass dependent kinetic isotope fractionation (Δ^xxx/198Hg)¬. External reproducibility should be monitored by analysis of secondary standards. For studies of MDF, we use an in-house secondary standard solution made from metallic Hg mined from Almaden Spain and obtain a δ202Hg of -0.55 ±0.06‰ (2SD). For studies of MIF, we use NRCC CRM DORM-2 (dogfish muscle) and obtain a mean value of δ202Hg of +0.19 ±0.13‰ (2SD), Δ²⁰¹Hg of +0.89 ±0.07‰ (2SD) , and Δ¹⁹⁹Hg of +1.07 ±0.08‰ (2SD).
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0792 Contaminants (0432)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1065 Major and trace element geochemistry
DE: 1094 Instruments and techniques
SC: Biogeosciences [B]
MN: 2007 Fall Meeting