[Ifeffit] P K-edge EXAFS

Hi there, I begin by examining phosphorus adsorption by goethite, hematite, and gibbsite. Why is it difficult, if not impossible, to obtain EXAFS spectra at the P-K edge that can be properly used, i.e., spectra with a high signal-to-noise ratio, especially for dilute samples? Would it be possible to use arsenic as a phosphorus proxy to get conclusions from As K-edge EXAFS data that could be extended to P? Thank you.