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

Myo-inositol hexakisphosphate, or phytic acid, (IP6) is a key organic phosphorus (P) compounds in soils and manures. Determinations IP6 in soils and manure extracts is 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, high-resolution mass spectrometry (HRMS) negative ion electrospray ionisation (ESI) has been shown to enable highly specific identifications of IP6 isolated from complex mixtures in combination with ion chromatography (IC). In this paper, ESI-HRMS and IC were applied to the identification and the quantification of IP6 isolated from soils and manures using NaOH-EDTA extraction and quantifications based on IC with ESI-HRMS and 31P NMR were compared. ESI-HRMS analysis of eluate trapped from IC unequivocally confirmed identification of IP6 from a soil extract. The ion suppression mechanism of the IC instrument facilitates a salt-free solution for the analyte, enabling good ionisation in the ESI. The compound was identified in the NMR by overlaying spectra of extracts of soils spiked with IP6 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 a more sensitive, rapid and reliable for the identification and quantification of 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.