Geochemical study on As-S system by X-ray spectroscopy

It is known that sulfide sometimes play a significant role in the geochemistry of arsenic under reducing conditions. So far, it has been assumed that sulfide primarily reduced the solubility and mobility of arsenic by precipitation of arsenic-sulfide minerals, As₂S₃, but recent studies indicate that under certain conditions, significant concentrations of soluble As-S compounds can exist in sulfidic waters. Thus, the question is whether they are As(III)-S species ("thioarsenites") or As(V)-S species ("thioarsenates"). A research group led by Dr. B. Planer-Friedrich (University of Bayreuth, Germany) has recently reported that use of X-ray absorption spectroscopy (XANES and EXAFS) can determine the concentration ratio of each species. The experiment was done at beamline BM20, ESRF. For more information, see the paper, "Discrimination of Thioarsenites and Thioarsenates by X-ray Absorption Spectroscopy", E. Suess et al., Anal. Chem., Article ASAP (2009), DOI: 10.1021/ac901094b