Methodology: X-ray spectromicroscopy data were collected using an energy dispersive silicon drift detector (Ketek with a 5mm2 sensitive area). A flow of helium was introduced between the X-ray optical hardware and the sample to reduce X-ray backscatter. An in-line monitor stick composed of hydroxyapatite was measured with each sample in order to identify and correct for any potential drift in monochrometer energy calibration that occurred during analyses (de Jonge et al., 2010). Clean areas of Teflon and cellulose acetate filters were examined as blanks and showed negligible background signal. The data for an individual P-NEXFS spectrum were normalized to create a relative intensity value ofapproximately 1 for post-edge area of the spectra (>2160 eV).

Sampling and analytical procedures: Phosphorus compounds were obtained from chemical supply houses. See papers cited below for details.

Instruments: X-ray fluorescence microscope located at beamline 2-ID-B at the Advanced Photon Source, Argonne National Laboratory. The beamline is optimized to examine samples over a 1–4 keV energy range using a focused X-ray beam with a spot size of approximately 60 nanometers squared . The energy was calibrated using a NIST standard reference material SRM2910 calcium hydroxyapatite. The whiteline energy of the standard was set to 2153 eV.

Data processing: P-NEXFS data were normalized to create a relative intensity value of approximately 1 for post-edge area of the spectra.