Mercury L alpha 1 High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy: A Versatile Speciation Probe for Mercury br

Mercury is in some sense an enigmatic element. The element and some ofits compounds are a natural part of the biogeochemical cycle; while many of these can bedeadly poisons at higher levels, environmental levels in the absence of anthropogeniccontributions would generally be below the threshold for concern. However, mercurypollution, particularly from burning fossil fuels such as coal, is providing dramatic andincreasing emissions into the environment. Because of this, the environmental chemistryand toxicology of mercury are of growing importance, with the fate of mercury being vitallydependent upon its speciation. X-ray absorption spectroscopy (XAS) provides a powerfultool forin situchemical speciation, but is severely limited by poor spectroscopic energyresolution. Here, we provide a systematic examination of mercury L alpha 1 high energyresolutionfluorescence detected XAS (HERFD-XAS) as an approach for chemicalspeciation of mercury, in quantitative comparison with conventional Hg LIII-edge XAS. We show that, unlike some lighter elements,chemical shifts in the L alpha 1 X-rayfluorescence energy can be safely neglected, so that mercury L alpha 1 HERFD-XAS can be treatedsimply as a high-resolution version of conventional XAS. We present spectra of a range of mercury compounds that may be relevantto the environmental and life science research and show that density functional theory can produce adequate simulations of thespectra. We discuss strengths and limitations of the method and quantitatively demonstrate improvements both in speciation for complex mixtures and in background rejection for low concentrations