EPMA WDS Peak Position Analysis of Mineral Chemistry in Fossils

Frequently in EPMA, the chemistry of an analyte (that is, the oxidation state and bonding of the elements in the material) is inferred from the composition, by stoichiometry or some other means. While this practice is usually adequate for determining the identity of pure single-phase materials, the results are often inconclusive when attempting similar analyses of complex mixtures composed of multiple compounds and phases. However, there are photoemission processes for certain elements in which a valence electron fills an atom’s core vacancy, resulting in characteristic X-rays that differ slightly in wavelength from the diagram line. In these circumstances, the peak position can be exploited by the analyst to determine an element’s oxidation state within the matrix. A practical problem, identifying sulfur mineralization within fossilized bones, is presented to demonstrate the method. The sulfur K lines have been shown to exhibit peak positions dependent upon oxidation state [1,2].