The Analysis of Soil Phosphorus by Icp And31p NMR Spectroscopy

The phosphorus content of 14 samples of UK soils has been determined. Aqueous tetra-n-butylammonium hydroxide was used to extract organic phosphates and these solutions were analyzed by Fourier transform 31P nuclear magnetic resonance spectroscopy. This permits the composition of this fraction of soil phosphorus to be expressed in terms of the following classes: (i) monoester phosphates (chiefly of inositol); (ii) diester phosphates (such as phospholipids and nucleotides); (iii) polyphosphates; and (iv) non-phosphates. The method is not suited to measuring the relative amounts of the key phosphate esters but it is sensitive enough to show the presence of other phosphorus compounds that are probably of pesticidal origin. The phosphorus content of the extracts was determined with an inductivity-coupled plasma source spectrometer, which was also used to measure the total phosphorus content of the soils after complete solubilization of samples via high temperature ignition followed by HClO4-HF treatment. This method gives higher phosphorus values than that using a mixture of strong mineral acids at 350°C, except for peaty soils.