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Molecular investigations of the nature, occurrence and behaviour of myo-inositol hexakisphosphate in soils using ion chromatography and high-resolution mass spectrometry

Bristol student theses: Doctoral ThesisDoctor of Philosophy (PhD)

Authors

  • Catherine McIntyre

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Abstract

Cycling of phosphorus (P) in the environment plays a fundamental role in agricultural production and the health of soil and freshwater ecosystems. However, the contribution of organic phosphorus (Po) species to the P biogeochemical cycle is not fully understood. Po characterisation of soil is frequently based on operational definitions of chemically extracted “pools” of P. While this approach is beneficial for the study of bulk chemistry processes, it provides limited insights into the molecular mechanisms of Po in the environment.
More detailed characterisations of soil Po have mostly focused on the use of 31P nuclear magnetic resonance (NMR) spectroscopy. NMR can identify classes of Po compounds, however, potentially many tens or hundreds of compounds can contribute to a given signal in an NMR spectrum. In contrast, high-resolution mass spectrometry (HRMS) can simultaneously resolve thousands of ions in a mass spectrum with capability being extended still further by combination with chromatography such as ion chromatography (IC) to provide enhanced characterisations and quantitative determinations.
Myo-inositol hexakisphosphate, (IP6), is an important Po compound, comprising up to 50% of Po in soils. The aim of my PhD was to develop and apply electrospray ionisation (ESI) HRMS and IC/HRMS techniques to the determination of IP6 in environmental matrices. ESI-HRMS was used to unequivocally identify the compound extracted from a soil matrix. IC quantification was compared to 31P NMR determination and found to be more rapid and sensitive than current NMR techniques. The extraction efficiency of IP6 from a range of soils was determined and correlated with soil characteristics, such as organic and metal content. The degradation of IP6 from poultry litter was investigated. Molecular characterisation of IP6 using the latest analytical methods was shown to facilitate the study of the molecular level processes involving Po in the environment to better understand the P biogeochemical cycle.

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Original languageEnglish
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Award date19 Mar 2019

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