Identification and quantification of myo-inositol hexakisphosphate in complex environmental matrices using ion chromatography and high-resolution mass spectrometry in comparison to 31P NMR spectroscopy.

ABSTRACT

Myo-inositol hexakisphosphate, or phytic acid, (myo-IP6) is a key organic phosphorus (P) compound in soils and manures. Determinations of myo-IP6 in soils and manure extracts are frequently performed by 31P NMR spectroscopy. This approach is time-consuming in terms of both sample preparation and instrument time, with uncertainties existing in relation to accuracy of identification and quantification due to potentially interfering resonances from co-extracted P species. In contrast, ion chromatography (IC) in combination with high-resolution mass spectrometry (HRMS) negative ion, electrospray ionisation (ESI) has been shown to enable highly specific identifications of myo-IP6 isolated from complex mixtures. In this paper, IC and ESI-HRMS were applied to the identification and the quantification of myo-IP6 isolated from soils and manures using NaOH-EDTA extraction, and quantifications based on IC. ESI-HRMS analysis of eluate trapped from IC unequivocally confirmed identification of myo-IP6 from a soil extract. The ion suppression cell of the IC instrument provides isolates of the analyte free of ionic components that would interfere with ESI. The myo-IP6 was identified in the NMR by comparing spectra of extracts of soils with and without authentic myo-IP6 "spiked" prior to extraction. Comparison of quantification via standard addition in IC and NMR analysis gave good correlation (r = 0.955). IC with ESI-HRMS was found to be more sensitive, rapid and reliable for the identification and quantification of myo-IP6 with a limit of detection (LOD) of 0.7 mg kg-1 and limit of quantification (LOQ) of 2.1 mg kg-1 using IC versus > 10 mg kg-1 LOD using 31P NMR.