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Utilising phase transfer agents to enhance rapid detection of chemical warfare nerve agents

Lee, Ching Ching (2021) Utilising phase transfer agents to enhance rapid detection of chemical warfare nerve agents. Masters by Research thesis, Murdoch University.

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Methylphosphonic acid (MPA) is the final degradant of many chemical warfare nerve agents (CWAs). Its detection in environmental and biological samples is a potential indicator of nerve agent use. Due to its high polarity and low volatility, analysis using gas chromatography-mass spectrometry (GC-MS) requires the derivatisation of MPA into a more volatile and less polar species. Currently, to derivatise MPA, it is typically necessary to perform the time-consuming and error-inducing water removal process prior to derivatisation. Therefore, it is of paramount importance to develop alternate rapid derivatisation methods for MPA to reduce the turnaround time for its detection and analysis.

Pilot studies undertaken at Murdoch University found that MPA could be derivatised without the removal of water via tert-butyldimethylsilylation using a two-phase aqueous/organic system. Although the reaction could be completed within 30 minutes, the derivatisation efficiency was found to be low. Therefore, this study aimed to improve the derivatisation efficiency of this method using phase transfer agents. Four phase transfer agents were tested (tetramethylammonium bromide, tetrabutylammonium bromide, tetrahexylammonium bromide and tetraoctylammonium bromide). Tetraoctylammonium bromide was discovered to significantly improve the efficiency of two-phase derivatisation in only half the time. Amount of phase transfer agent, reaction temperature and time were also optimised. Optimal derivatisation occurred in 15 minutes at 60 °C using 10 mol% of phase transfer agent. Initial attempts to quantify derivatisation efficiency using 31P-NMR to determine the concentration of MPA remaining in aqueous phase were unsuccessful. However, quantification of the derivative using GC-MS, revealed the efficiency of this two-phase phase transfer agent method was 30.25 ± 1.78%, a tenfold increase compared to the previous method. The qualitative detection limit of this phase transfer agent method was 1 ppm, which was yet another significant improvement from the initial 1000 ppm. Attempts were also made to isolate pure bis[tert-butyl(dimethyl)silyl] ester of MPA for the first time, but were terminated due to time constraint. However, high performance liquid chromatography (HPLC) separation results suggested that isolation of the derivative is possible.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation(s): Mathematics, Statistics, Chemistry and Physics
Notes: Accelerated Research Masters with Training
Supervisor(s): Henry, David and Laird, Damian
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