Application of a wavelength-dispersive particle-induced X-ray emission system to chemical speciation of phosphorus and sulfur in lake sediment samples

The chemical speciation of phosphorus and sulfur in lake sediment was performed by analyzing Kα X-ray spectra recorded with a high-resolution wavelength-dispersive particle-induced X-ray emission (WD-PIXE) system. The concentrations of phosphorus and sulfur in the sediment were 2500 and 7000 ppm, respectively. To measure both minor elements in a reasonable measurement time, a 2-MeV proton beam with a high current density (6 nA/mm2) was used for the chemical speciation. The possible chemical state change caused by the proton irradiation was studied in order to determine the maximal irradiation time without significant change. We found that the chemical states of phosphorus and sulfur were stable under a beam current density of 6 nA/mm2 and a measurement time of 60 min (phosphorus) and 90 min (sulfur). The chemical states of phosphorus and sulfur were determined to be P5+ and a mixture of S2− and S6+, respectively.