Cr(VI) Reduction on Fe(III) Solid Surfaces at Vacuum Pressures

ABSTRACT Here, we investigate how the oxidation state of Cr adsorbed to solid surfaces can change during XPS analysis. Experiments are performed to test how Fe(III) solid surfaces, aqueous chemistry, and XPS vacuum conditions affected the measured Cr oxidation state. While oxidized Cr(VI) adsorbs onto nonreducing solid surfaces in the experiments, reduced Cr(III) is primarily measured by XPS. The reduction of adsorbed Cr(VI) occurs under the vacuum conditions of the XPS as CO 2 , O 2 , and H 2 O are removed from the sample surface. These results suggest that Fe(III) solid surfaces exposed to high‐vacuum conditions and/or X‐rays can cause the reduction of Cr or other elements with a high redox potential contained on that surface.