Improvement of 31P NMR Spectral Resolution by 8-Hydroxyquinoline Precipitation of Paramagnetic Fe and Mn in Environmental Samples

Solution 31P nuclear magnetic resonance (NMR) spectroscopy is currently the main method for the characterization of phosphorus (P) forms in environment samples. However, identification and quantification of P compounds may be hampered by poor resolution of spectra caused by paramagnetic Fe and Mn. In this study, a novel technique was developed to improve spectral resolution by removing paramagnetic Fe and Mn from alkaline extracts via 8-hydroxyquinoline (8-HOQ) precipitation. Batch experiments showed that both Fe and Mn were effectively removed by the precipitation at pH 9.0, with the removal efficiencies of 83−91% for Fe and 67−78% for Mn from the extracts of five different environmental samples, while little effect was found on concentration of total P. The 31P NMR analysis of a model P solution showed that addition of 8-HOQ and its precipitation with metal ions did not alter P forms. Further analyses of the five extracts with 31P NMR spectroscopy demonstrated that the 8-HOQ precipitation was an ideal m...