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

Catherine A McIntyre; Jennifer J L Arkell; Christopher J Arthur; Paul G Lawrence; Craig P Butts; Charlotte E M Lloyd; Penny J Johnes; Richard P Evershed

doi:10.1016/j.talanta.2019.120188

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

Talanta. 2020 Apr 1:210:120188. doi: 10.1016/j.talanta.2019.120188. Epub 2019 Jul 31.

Authors

Catherine A McIntyre¹, Jennifer J L Arkell¹, Christopher J Arthur², Paul G Lawrence², Craig P Butts², Charlotte E M Lloyd¹, Penny J Johnes³, Richard P Evershed⁴

Affiliations

¹ Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom.
² School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom.
³ School of Geographical Sciences, University of Bristol, University Road, Bristol, BS8 1SS, United Kingdom.
⁴ Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom. Electronic address: r.p.evershed@bristol.ac.uk.

PMID: 31987164
DOI: 10.1016/j.talanta.2019.120188

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.

Keywords: High-resolution mass spectrometry; Ion chromatography; NMR; Phytic acid; Soil.