Soil Organic Phosphorus Speciation Using Spectroscopic Techniques

Spectral sensitivity of solution 31P NMR spectroscopy is improved by narrowing the soil to solution ratio to 1:4 for pasture soils of low organic P content

“…4 and 5). This can be attributed to the greater density of P in the NMR tube at the 1:4 ratio than at the 1:10 ratio (Doolette and Smernik, 2011). Furthermore, the signal resolution (peak width) appears identical for corresponding 1:4 and 1:10 extracts, clearly indicating that the higher paramagnetic metal concentrations in the 1:4 extracts are not causing additional line broadening for these soils (Figs.…”

“…NMR probes that accommodate 10 mm rather 5 mm diameter tubes) (Preston, 1996); and/or 4) optimising relaxation delays between pulses for maximum sensitivity (Cade-Menun and Liu, 2014). These strategies have been discussed in several reviews (Cade-Menun, 2005;Cade-Menun and Liu, 2014;Cade-Menun and Preston, 1996;Doolette and Smernik, 2011;Preston, 1996) and most studies employ a combination of these strategies in an effort to increase sensitivity.…”

“…However, since signal-to-noise ratio (a direct measure of sensitivity) only increases with the square root of the number of scans, improving sensitivity in this way is costly and timeconsuming. Given that spectral signal is linearly related to the concentration of P nuclei in the analysed sample, a better approach to improving sensitivity of 31 P NMR spectra than through collecting more scans is to increase the sample P concentration (Cade-Menun and Liu, 2014;Doolette and Smernik, 2011). Several strategies have been suggested, including: 1) optimising the extraction procedure to increase extraction efficiency (e.g.…”

“…The main limitation of solution 31 P NMR spectroscopy for determining the chemical nature of soil organic P is poor spectral sensitivity (Doolette and Smernik, 2011), which specifically refers to the ability to detect signal against background noise. The innately insensitive nature of NMR spectroscopy requires the collection of many scans to obtain adequate signal.…”

Solution Phosphorus-31 Nuclear Magnetic Resonance Spectroscopy of Soils from 2005 to 2013: A Review of Sample Preparation and Experimental Parameters

“…Full chemical speciation to identify specific P forms requires either extraction for individual forms (e.g., for phospholipids or RNA) or advanced spectroscopic techniques such as 31 P NMR spectroscopy or x-ray adsorption near-edge structure (XANES) spectroscopy (e.g., Kizewski et al, 2011;Doolette and Smernik, 2011). The XANES spectroscopy (P K-edge or P L 2,3 -edge) has been most successfully used to characterize inorganic P forms and has been used to identify Ca-bound P (e.g., hydroxyapatite and octocalcium phosphate), Fe-bound P (e.g., strengite), and Al-bound P (e.g., variscite) in soil samples (e.g., Kizewski et al, 2011, and references therein).…”