Solution ³¹Phosphorus Nuclear Magnetic Resonance Analysis of Acid-Extractable Phosphates in Animal Feces

Characterizing phosphates in animal fecal and manure samples is of interest to environmental-monitoring research efforts. Acid extraction removes relatively mobile phosphates from samples, offering a better indicator of the mobility of phosphates in environment, but acidic extracts impose challenges to the solution phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectroscopy, which is commonly used for analyzing phosphates in environmental samples. Acid-extractable metals precipitate phosphates in the alkaline condition under which solution ³¹P NMR experiment runs, blurring the spectrum for adequate analysis. We found that neutralizing acid extracts with 0.5 M sodium hydroxide (NaOH) plus 50 mM ethylenediaminetetraacetic acid (EDTA) before freeze drying eliminated the chemical interferences otherwise observed. The resulting ³¹P NMR spectra can be used to quantify acid-soluble phytate and other phosphates in animal fecal and manure samples. The improvement in detection will support efforts to investigate the mobility of phosphates in feces and manures used as land amendments.