An improved technique for the determination of organic phosphorus in sediments and soils by 31P nuclear magnetic resonance spectroscopy

Knowledge of organic phosphorus ( P) species quantity and distribution in sediments and soils is needed to determine the potential for aquatic and terrestrial organism growth. This can be achieved with P-31 nuclear magnetic resonance spectroscopy (NMR), but resolving peaks within spectra can be problematic because of broadening via paramagnetics, which can cause peaks to overlap. We compared P-31 NMR spectra of NaOH-EDTA extracts of three sediments and three soils to those that had first been pre-treated with Ca-EDTA-dithionite to remove Fe and Mn, paramagnetics that cause broadening of peaks, but leave organic P alone. Broadening of peaks in Ca-EDTA-dithionite pre-treated samples decreased by 46% and revealed peaks that were hidden compared to untreated samples. The spectrum of one pre-treated soil was similar if not better than the same soil that had received pre-treatment with Chelex resin ( also to remove paramagnetics). Therefore, pre-treatment with Ca-EDTA-dithionite is recommended as a simple and cost-effective method for improving organic P identification and determination in subsequent NaOH-EDTA extracts of sediments and soils rich in Fe and Mn.