A new solution <sup>31</sup>P NMR sample preparation scheme for marine sediments
Defforey, D., Cade-Menun, B.J., Paytan, A. (2017). A new solution 31P NMR sample preparation scheme for marine sediments, 15(4), 381-393. http://dx.doi.org/10.1002/lom3.10166
Plain language summary
Phosphorus (P) is an essential nutrient for all organisms, so research is conducted to measure the forms and concentrations of P in many different environments . In oceans, P concentrations can be quite low, which can make it difficult to measure P concentrations. One technique that is used to determine P forms in environmental samples is 31P nuclear magnetic resonance spectroscopy (P-NMR). The objective of this study was to find ways to improve P-NMR studies of marine sediments, which can be a problem due to low P concentrations. This project tested a pre-concentration method that improved the use of P-NMR in marine sediments from various locations world-wide.
A new approach for the preparation of marine sediment samples for solution 31P nuclear magnetic resonance spectroscopy ( P NMR) has been developed and tested. This approach addresses important aspects associated with sample pretreatments for marine sediments, including the effects of sample pretreatment on sedimentary P composition. The method increases the signals of low abundance P species in P NMR spectra by quantitatively and precisely removing up to 80% of inorganic P (orthophosphate) from sediment samples while causing minimal alteration of the chemical structure of organic P compounds. This method uses a reductive step to solubilize P bound to iron oxyhydroxides, followed by a low pH digestion to extract P from authigenic and biogenic apatite, as well as P bound to calcium carbonate. These P forms combined represent the most abundant inorganic P reservoir in marine sediments. The sample residue is then extracted in an alkaline solvent, 0.25 M NaOH with 0.05 M Na2EDTA, and processed for P NMR spectroscopy. The method was tested on natural marine sediment samples from different localities with high inorganic P content (>85% molybdate reactive P), and allowed for the detection of orthophosphate monoesters and pyrophosphate in samples for which only an orthophosphate signal could be resolved with an NaOH-EDTA extraction alone. This new approach will allow the use of P NMR on samples for which low organic P concentrations previously hindered the use of this tool, and will help answer longstanding question regarding the fate of organic P in marine sediments. 31 31 31 31