Identification of scyllo-inositol phosphates in soil by solution phosphorus-31 nuclear magnetic resonance spectroscopy

A large proportion of the organic P in soils can occur as scyllo-inositol phosphates. These compounds are rarely detected elsewhere in nature and remain poorly understood, partly because conventional procedures for their determination are lengthy and erroneous. We report a straightforward procedure for the determination of scyllo-inositol phosphates in soil extracts using solution 31P nuclear magnetic resonance (NMR) spectroscopy. Solution 31P NMR chemical shifts of a range of synthetic scyllo-inositol phosphate esters were determined in alkaline solution. Of these, only the signal corresponding to scyllo-inositol hexakisphosphate at approximately 4.2 ppm was identified in soil NaOH–EDTA extracts, constituting between 6.5 and 9.8% of the NaOH–EDTA extracted P. This signal has been previously assigned to choline phosphate, but we confirmed it to be an inositol phosphate using hypobromite oxidation, a procedure that destroys all organic matter except inositol phosphates. Lower order scyllo-inositol phosphate esters were not identified in the extracts studied here, and literature reports suggest that they probably occur in insufficient concentrations to be detected by this procedure. The identification of scyllo-inositol hexakisphosphate in soils and other environmental samples will allow its quantification in a range of environments, and facilitate research into the origins and function of this enigmatic compound