The Application and Potential Artifacts of Zeeman Cold Vapor Atomic Absorption Spectrometry in Mercury Stable Isotope Analysis

Zeeman cold vapor atomic absorption spectrometry (CVAAS) has been widely used for environmental mercury (Hg) detection and quantification for decades, but little is known about its utility and potential artifacts in analyzing Hg with varying isotope compositions. We show that each Hg isotope responds differently by CVAAS analysis, with ²⁰⁰ Hg and ²⁰² Hg isotopes exhibiting signal intensities ∼10 times greater than those of ¹⁹⁸ Hg and ²⁰¹ Hg isotopes. However, all Hg isotopes show a linear correlation between Hg concentration and signal intensity, validated by both measurements and theoretical simulations. Zeeman CVAAS could thus offer a convenient, inexpensive tool for determining Hg isotopes, particularly in using one or two enriched Hg isotopes for tracing Hg biogeochemical transformations, such as partitioning, ion exchange, sorption-desorption, and methylation-demethylation in environmental matrices. We also caution that care must be taken when CVAAS is used for quantifying Hg in samples with changing isotope compositions to avoid measurement errors.