Methodological artefacts in the XANES analysis of hexa-coordinated pentavalent arsenic

Abstract

Using XANES, we studied the recently identified hexa-coordinated pentavalent arsenic, specifically, octahedral As(V)-glycerol compound As(V)(OCH₂CH(O)CH₂OH)₃. It is stable at all pHs tested (1–12), but is transformed to the conventional tetrahedral AsO₄³⁻ compound in the presence of water. Dehydration of environmental samples (i.e., Manitoba maple leaf and hare muscle) spiked with a AsO₄³⁻ standard resulted in XANES features of the As(V)-glycerol compound. Therefore the compound we hypothesize to be the As(V)-glycerol in environmental samples is likely only visible using XAS analysis, and does not appear to survive wet environments such as those in biological systems, where toxicity may be experienced, or in conventional speciation methods, which generally use aqueous separation techniques.