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Progress in quantitative elemental analyses in high P–T fluids using synchrotron x-ray fluorescence (SXRF)

Two different experimental set-ups have been installed at ID22 beamline (ESRF) for synchrotron x-ray fluorescence (SXRF) analyses in diamond anvil cells (DACs). The set-ups differ from each other by the incident energy, the focusing device and the collection geometry. Analyses of standard aqueous solutions containing well-known concentrations of Sr and Rb have been performed in both experimental configurations and the detection limits (DLs) determined. The most important factors contributing to both the fluorescence intensity yield and the background have been discussed in order to determine the experimental configuration providing the lowest detection limits. The limiting factor for the analyses at very low concentrations is the background arising from the Compton and Rayleigh scattering in the diamond anvils, which have a major contribution in the collection geometry imposed by the design of the DAC. We show that slight improvements of this design enable the acquisition of the fluorescence at 150°, permitting SXRF analyses of aqueous solutions to be performed at the 40 ppm level in a standard DAC working to 10 GPa and 600 °C, at least.